diff --git a/.claude/agents/action-planning-agent.md b/.claude/agents/action-planning-agent.md
index 28c1c447..90920b48 100644
--- a/.claude/agents/action-planning-agent.md
+++ b/.claude/agents/action-planning-agent.md
@@ -829,6 +829,12 @@ Generate at `.workflow/active/{session_id}/plan.json` following `plan-overview-b
 
 **Generation Timing**: After all `.task/IMPL-*.json` files are generated, aggregate into plan.json.
 
+**Validation**: After writing plan.json and task files, validate with json_builder:
+```bash
+ccw tool exec json_builder '{"cmd":"validate","target":"<session>/plan.json","schema":"plan"}'
+ccw tool exec json_builder '{"cmd":"validate","target":"<session>/.task/IMPL-001.json","schema":"task"}'
+```
+
 ### 2.3 IMPL_PLAN.md Structure
 
 **Template-Based Generation**:
diff --git a/.claude/agents/cli-explore-agent.md b/.claude/agents/cli-explore-agent.md
index 9bd7392a..61136fe2 100644
--- a/.claude/agents/cli-explore-agent.md
+++ b/.claude/agents/cli-explore-agent.md
@@ -5,6 +5,7 @@ description: |
   Orchestrates 4-phase workflow: Task Understanding → Analysis Execution → Schema Validation → Output Generation.
   Spawned by /explore command orchestrator.
 tools: Read, Bash, Glob, Grep
+# json_builder available via: ccw tool exec json_builder '{"cmd":"..."}' (Bash)
 color: yellow
 ---
 
@@ -66,9 +67,9 @@ Phase 4: Output Generation
    Store result as `project_structure` for module-aware file discovery in Phase 2.
 
 2. **Output Schema Loading** (if output file path specified in prompt):
-   - Exploration output → `cat ~/.ccw/workflows/cli-templates/schemas/explore-json-schema.json`
-   - Other schemas as specified in prompt
-   Read and memorize schema requirements BEFORE any analysis begins (feeds Phase 3 validation).
+   - Get schema summary: `ccw tool exec json_builder '{"cmd":"info","schema":"explore"}'` (or "diagnosis" for bug analysis)
+   - Initialize output file: `ccw tool exec json_builder '{"cmd":"init","schema":"explore","output":"<output_path>"}'`
+   - The tool returns requiredFields, arrayFields, and enumFields — memorize these for Phase 2.
 
 3. **Project Context Loading** (from spec system):
    - Load exploration specs using: `ccw spec load --category exploration`
@@ -150,55 +151,56 @@ RULES: {from prompt, if template specified} | analysis=READ-ONLY
 ---
 
 <schema_validation>
-## Phase 3: Schema Validation
+## Phase 3: Incremental Build & Validation (via json_builder)
 
-### CRITICAL: Schema Compliance Protocol
+**This phase replaces manual JSON writing + self-validation with tool-assisted construction.**
 
-**This phase is MANDATORY when schema file is specified in prompt.**
-
-**Step 1: Read Schema FIRST**
-```
-Read(schema_file_path)
+**Step 1: Set text fields** (discovered during Phase 2 analysis)
+```bash
+ccw tool exec json_builder '{"cmd":"set","target":"<output_path>","ops":[
+  {"path":"project_structure","value":"..."},
+  {"path":"patterns","value":"..."},
+  {"path":"dependencies","value":"..."},
+  {"path":"integration_points","value":"..."},
+  {"path":"constraints","value":"..."}
+]}'
 ```
 
-**Step 2: Extract Schema Requirements**
+**Step 2: Append file entries** (as discovered — one `set` per batch)
+```bash
+ccw tool exec json_builder '{"cmd":"set","target":"<output_path>","ops":[
+  {"path":"relevant_files[+]","value":{"path":"src/auth.ts","relevance":0.9,"rationale":"Contains AuthService.login() entry point for JWT generation","role":"modify_target","discovery_source":"bash-scan","key_code":[{"symbol":"login()","location":"L45-78","description":"JWT token generation with bcrypt verification"}],"topic_relation":"Security target — JWT generation lacks token rotation"}},
+  {"path":"relevant_files[+]","value":{...}}
+]}'
+```
 
-Parse and memorize:
-1. **Root structure** - Is it array `[...]` or object `{...}`?
-2. **Required fields** - List all `"required": [...]` arrays
-3. **Field names EXACTLY** - Copy character-by-character (case-sensitive)
-4. **Enum values** - Copy exact strings (e.g., `"critical"` not `"Critical"`)
-5. **Nested structures** - Note flat vs nested requirements
+The tool **automatically validates** each operation:
+- enum values (role, discovery_source) → rejects invalid
+- minLength (rationale >= 10) → rejects too short
+- type checking → rejects wrong types
 
-**Step 3: File Rationale Validation** (MANDATORY for relevant_files / affected_files)
+**Step 3: Set metadata**
+```bash
+ccw tool exec json_builder '{"cmd":"set","target":"<output_path>","ops":[
+  {"path":"_metadata.timestamp","value":"auto"},
+  {"path":"_metadata.task_description","value":"..."},
+  {"path":"_metadata.source","value":"cli-explore-agent"},
+  {"path":"_metadata.exploration_angle","value":"..."},
+  {"path":"_metadata.exploration_index","value":1},
+  {"path":"_metadata.total_explorations","value":2}
+]}'
+```
 
-Every file entry MUST have:
-- `rationale` (required, minLength 10): Specific reason tied to the exploration topic, NOT generic
-  - GOOD: "Contains AuthService.login() which is the entry point for JWT token generation"
-  - BAD: "Related to auth" or "Relevant file"
-- `role` (required, enum): Structural classification of why it was selected
-- `discovery_source` (optional but recommended): How the file was found
-- `key_code` (strongly recommended for relevance >= 0.7): Array of {symbol, location?, description}
-  - GOOD: [{"symbol": "AuthService.login()", "location": "L45-L78", "description": "JWT token generation with bcrypt verification, returns token pair"}]
-  - BAD: [{"symbol": "login", "description": "login function"}]
-- `topic_relation` (strongly recommended for relevance >= 0.7): Connection from exploration angle perspective
-  - GOOD: "Security exploration targets this file because JWT generation lacks token rotation"
-  - BAD: "Related to security"
+**Step 4: Final validation**
+```bash
+ccw tool exec json_builder '{"cmd":"validate","target":"<output_path>"}'
+```
+Returns `{valid, errors, warnings, stats}`. If errors exist → fix with `set` → re-validate.
 
-**Step 4: Pre-Output Validation Checklist**
-
-Before writing ANY JSON output, verify:
-
-- [ ] Root structure matches schema (array vs object)
-- [ ] ALL required fields present at each level
-- [ ] Field names EXACTLY match schema (character-by-character)
-- [ ] Enum values EXACTLY match schema (case-sensitive)
-- [ ] Nested structures follow schema pattern (flat vs nested)
-- [ ] Data types correct (string, integer, array, object)
-- [ ] Every file in relevant_files has: path + relevance + rationale + role
-- [ ] Every rationale is specific (>10 chars, not generic)
-- [ ] Files with relevance >= 0.7 have key_code with symbol + description (minLength 10)
-- [ ] Files with relevance >= 0.7 have topic_relation explaining connection to angle (minLength 15)
+**Quality reminders** (enforced by tool, but be aware):
+- `rationale`: Must be specific, not generic ("Related to auth" → rejected by semantic check)
+- `key_code`: Strongly recommended for relevance >= 0.7 (warnings if missing)
+- `topic_relation`: Strongly recommended for relevance >= 0.7 (warnings if missing)
 </schema_validation>
 
 ---
@@ -212,16 +214,12 @@ Brief summary:
 - Task completion status
 - Key findings summary
 - Generated file paths (if any)
+- Validation result (from Phase 3 Step 4)
 
-### File Output (as specified in prompt)
+### File Output
 
-**MANDATORY WORKFLOW**:
-
-1. `Read()` schema file BEFORE generating output
-2. Extract ALL field names from schema
-3. Build JSON using ONLY schema field names
-4. Validate against checklist before writing
-5. Write file with validated content
+File is already written by json_builder during Phase 3 (init + set operations).
+Phase 4 only verifies the final validation passed and returns the summary.
 </output_generation>
 
 ---
@@ -243,28 +241,19 @@ Brief summary:
 
 **ALWAYS**:
 1. **Search Tool Priority**: ACE (`mcp__ace-tool__search_context`) → CCW (`mcp__ccw-tools__smart_search`) / Built-in (`Grep`, `Glob`, `Read`)
-2. Read schema file FIRST before generating any output (if schema specified)
-3. Copy field names EXACTLY from schema (case-sensitive)
-4. Verify root structure matches schema (array vs object)
-5. Match nested/flat structures as schema requires
-6. Use exact enum values from schema (case-sensitive)
-7. Include ALL required fields at every level
-8. Include file:line references in findings
-9. **Every file MUST have rationale**: Specific selection basis tied to the topic (not generic)
-10. **Every file MUST have role**: Classify as modify_target/dependency/pattern_reference/test_target/type_definition/integration_point/config/context_only
-11. **Track discovery source**: Record how each file was found (bash-scan/cli-analysis/ace-search/dependency-trace/manual)
-12. **Populate key_code for high-relevance files**: relevance >= 0.7 → key_code array with symbol, location, description
-13. **Populate topic_relation for high-relevance files**: relevance >= 0.7 → topic_relation explaining file-to-angle connection
+2. **Use json_builder** for all JSON output: `init` → `set` (incremental) → `validate`
+3. Include file:line references in findings
+4. **Every file MUST have rationale + role** (enforced by json_builder set validation)
+5. **Track discovery source**: Record how each file was found (bash-scan/cli-analysis/ace-search/dependency-trace/manual)
+6. **Populate key_code + topic_relation for high-relevance files** (relevance >= 0.7; json_builder warns if missing)
 
 **Bash Tool**:
 - Use `run_in_background=false` for all Bash/CLI calls to ensure foreground execution
 
 **NEVER**:
-1. Modify any files (read-only agent)
-2. Skip schema reading step when schema is specified
-3. Guess field names - ALWAYS copy from schema
-4. Assume structure - ALWAYS verify against schema
-5. Omit required fields
+1. Modify any source code files (read-only agent — json_builder writes only output JSON)
+2. Hand-write JSON output — always use json_builder
+3. Skip the `validate` step before returning
 </operational_rules>
 
 <output_contract>
@@ -282,11 +271,8 @@ When exploration is complete, return one of:
 
 Before returning, verify:
 - [ ] All 4 phases were executed (or skipped with justification)
-- [ ] Schema was read BEFORE output generation (if schema specified)
-- [ ] All field names match schema exactly (case-sensitive)
-- [ ] Every file entry has rationale (specific, >10 chars) and role
-- [ ] High-relevance files (>= 0.7) have key_code and topic_relation
+- [ ] json_builder `init` was called at start
+- [ ] json_builder `validate` returned `valid: true` (or all errors were fixed)
 - [ ] Discovery sources are tracked for all findings
-- [ ] No files were modified (read-only agent)
-- [ ] Output format matches schema root structure (array vs object)
+- [ ] No source code files were modified (read-only agent)
 </quality_gate>
diff --git a/.claude/agents/cli-lite-planning-agent.md b/.claude/agents/cli-lite-planning-agent.md
index 0a99420b..b9da78ef 100644
--- a/.claude/agents/cli-lite-planning-agent.md
+++ b/.claude/agents/cli-lite-planning-agent.md
@@ -139,16 +139,15 @@ When `process_docs: true`, generate planning-context.md before sub-plan.json:
 
 ## Schema-Driven Output
 
-**CRITICAL**: Read the schema reference first to determine output structure:
-- `plan-overview-base-schema.json` → Implementation plan with `approach`, `complexity`
-- `plan-overview-fix-schema.json` → Fix plan with `root_cause`, `severity`, `risk_level`
+**CRITICAL**: Get schema info via json_builder to determine output structure:
+- `ccw tool exec json_builder '{"cmd":"info","schema":"plan"}'` → Implementation plan with `approach`, `complexity`
+- `ccw tool exec json_builder '{"cmd":"info","schema":"plan-fix"}'` → Fix plan with `root_cause`, `severity`, `risk_level`
 
-```javascript
-// Step 1: Always read schema first
-const schema = Bash(`cat ${schema_path}`)
-
-// Step 2: Generate plan conforming to schema
-const planObject = generatePlanFromSchema(schema, context)
+After generating plan.json and .task/*.json, validate:
+```bash
+ccw tool exec json_builder '{"cmd":"validate","target":"<session>/plan.json","schema":"plan"}'
+# For each task file:
+ccw tool exec json_builder '{"cmd":"validate","target":"<session>/.task/TASK-001.json","schema":"task"}'
 ```
 
 </schema_driven_output>
@@ -863,7 +862,7 @@ function validateTask(task) {
 
 **ALWAYS**:
 - **Search Tool Priority**: ACE (`mcp__ace-tool__search_context`) → CCW (`mcp__ccw-tools__smart_search`) / Built-in (`Grep`, `Glob`, `Read`)
-- **Read schema first** to determine output structure
+- **Get schema info via json_builder** to determine output structure
 - Generate task IDs (TASK-001/TASK-002 for plan, FIX-001/FIX-002 for fix-plan)
 - Include depends_on (even if empty [])
 - **Assign cli_execution_id** (`{sessionId}-{taskId}`)
@@ -981,7 +980,7 @@ Upon completion, return one of:
 
 Before returning, verify:
 
-- [ ] Schema reference was read and output structure matches schema type (base vs fix)
+- [ ] Schema info was obtained via json_builder and output structure matches schema type (base vs fix)
 - [ ] All tasks have valid IDs (TASK-NNN or FIX-NNN format)
 - [ ] All tasks have 2+ implementation steps
 - [ ] All convergence criteria are quantified and testable (no vague language)
diff --git a/.claude/agents/issue-plan-agent.md b/.claude/agents/issue-plan-agent.md
index f8701b0a..085033c3 100644
--- a/.claude/agents/issue-plan-agent.md
+++ b/.claude/agents/issue-plan-agent.md
@@ -348,7 +348,7 @@ Write({ file_path: filePath, content: newContent })
 .workflow/issues/solutions/{issue-id}.jsonl
 ```
 
-Each line is a solution JSON containing tasks. Schema: `cat ~/.ccw/workflows/cli-templates/schemas/solution-schema.json`
+Each line is a solution JSON containing tasks. Schema: `ccw tool exec json_builder '{"cmd":"info","schema":"solution"}'`
 
 ### 2.2 Return Summary
 
@@ -388,7 +388,7 @@ Each line is a solution JSON containing tasks. Schema: `cat ~/.ccw/workflows/cli
 
 **ALWAYS**:
 1. **Search Tool Priority**: ACE (`mcp__ace-tool__search_context`) → CCW (`mcp__ccw-tools__smart_search`) / Built-in (`Grep`, `Glob`, `Read`)
-2. Read schema first: `cat ~/.ccw/workflows/cli-templates/schemas/solution-schema.json`
+2. Get schema info: `ccw tool exec json_builder '{"cmd":"info","schema":"solution"}'` (replaces reading raw schema)
 3. Use ACE semantic search as PRIMARY exploration tool
 4. Fetch issue details via `ccw issue status <id> --json`
 5. **Analyze failure history**: Check `issue.feedback` for type='failure', stage='execute'
@@ -408,6 +408,11 @@ Each line is a solution JSON containing tasks. Schema: `cat ~/.ccw/workflows/cli
 4. **Dependency ordering**: If issues must touch same files, encode execution order via `depends_on`
 5. **Scope minimization**: Prefer smaller, focused modifications over broad refactoring
 
+**VALIDATE**: After writing solution JSONL, validate each solution:
+```bash
+ccw tool exec json_builder '{"cmd":"validate","target":".workflow/issues/solutions/<issue-id>.jsonl","schema":"solution"}'
+```
+
 **NEVER**:
 1. Execute implementation (return plan only)
 2. Use vague criteria ("works correctly", "good performance")
diff --git a/.claude/commands/workflow/spec/setup.md b/.claude/commands/workflow/spec/setup.md
index 6c4aa08e..f4e765d8 100644
--- a/.claude/commands/workflow/spec/setup.md
+++ b/.claude/commands/workflow/spec/setup.md
@@ -129,7 +129,7 @@ Task(
 Analyze project for workflow initialization and generate .workflow/project-tech.json.
 
 ## MANDATORY FIRST STEPS
-1. Execute: cat ~/.ccw/workflows/cli-templates/schemas/project-tech-schema.json (get schema reference)
+1. Execute: ccw tool exec json_builder '{"cmd":"info","schema":"tech"}' (get schema summary)
 2. Execute: ccw tool exec get_modules_by_depth '{}' (get project structure)
 
 ## Task
diff --git a/.claude/skills/review-cycle/phases/review-module.md b/.claude/skills/review-cycle/phases/review-module.md
index 9fcc99e6..c8312103 100644
--- a/.claude/skills/review-cycle/phases/review-module.md
+++ b/.claude/skills/review-cycle/phases/review-module.md
@@ -401,7 +401,7 @@ Task(
     1. Read review state: ${reviewStateJsonPath}
     2. Get target files: Read resolved_files from review-state.json
     3. Validate file access: bash(ls -la ${targetFiles.join(' ')})
-    4. Execute: cat ~/.ccw/workflows/cli-templates/schemas/review-dimension-results-schema.json (get output schema reference)
+    4. Execute: ccw tool exec json_builder '{"cmd":"info","schema":"review-dim"}' (get output schema summary)
     5. Read: .workflow/project-tech.json (technology stack and architecture context)
     6. Read: .workflow/specs/*.md (user-defined constraints and conventions to validate against)
 
@@ -456,7 +456,7 @@ Task(
     ${getDimensionGuidance(dimension)}
 
     ## Success Criteria
-    - [ ] Schema obtained via cat review-dimension-results-schema.json
+    - [ ] Schema obtained via json_builder info
     - [ ] All target files analyzed for ${dimension} concerns
     - [ ] All findings include file:line references with code snippets
     - [ ] Severity assessment follows established criteria (see reference)
@@ -505,7 +505,7 @@ Task(
     2. Read affected file: ${file}
     3. Identify related code: bash(grep -r "import.*${basename(file)}" ${projectDir}/src --include="*.ts")
     4. Read test files: bash(find ${projectDir}/tests -name "*${basename(file, '.ts')}*" -type f)
-    5. Execute: cat ~/.ccw/workflows/cli-templates/schemas/review-deep-dive-results-schema.json (get output schema reference)
+    5. Execute: ccw tool exec json_builder '{"cmd":"info","schema":"review-deep"}' (get output schema summary)
     6. Read: .workflow/project-tech.json (technology stack and architecture context)
     7. Read: .workflow/specs/*.md (user-defined constraints for remediation compliance)
 
@@ -538,7 +538,7 @@ Task(
        - Impact assessment and rollback strategy
 
     ## Success Criteria
-    - [ ] Schema obtained via cat review-deep-dive-results-schema.json
+    - [ ] Schema obtained via json_builder info
     - [ ] Root cause clearly identified with supporting evidence
     - [ ] Remediation plan is step-by-step actionable with exact file:line references
     - [ ] Each step includes specific commands and validation tests
diff --git a/.claude/skills/review-cycle/phases/review-session.md b/.claude/skills/review-cycle/phases/review-session.md
index 03c6e041..a0ba5c46 100644
--- a/.claude/skills/review-cycle/phases/review-session.md
+++ b/.claude/skills/review-cycle/phases/review-session.md
@@ -412,7 +412,7 @@ Task(
     2. Read completed task summaries: bash(find ${summariesDir} -name "IMPL-*.md" -type f)
     3. Get changed files: bash(cd ${workflowDir} && git log --since="${sessionCreatedAt}" --name-only --pretty=format: | sort -u)
     4. Read review state: ${reviewStateJsonPath}
-    5. Execute: cat ~/.ccw/workflows/cli-templates/schemas/review-dimension-results-schema.json (get output schema reference)
+    5. Execute: ccw tool exec json_builder '{"cmd":"info","schema":"review-dim"}' (get output schema summary)
     6. Read: .workflow/project-tech.json (technology stack and architecture context)
     7. Read: .workflow/specs/*.md (user-defined constraints and conventions to validate against)
 
@@ -467,7 +467,7 @@ Task(
     ${getDimensionGuidance(dimension)}
 
     ## Success Criteria
-    - [ ] Schema obtained via cat review-dimension-results-schema.json
+    - [ ] Schema obtained via json_builder info
     - [ ] All changed files analyzed for ${dimension} concerns
     - [ ] All findings include file:line references with code snippets
     - [ ] Severity assessment follows established criteria (see reference)
@@ -516,7 +516,7 @@ Task(
     2. Read affected file: ${file}
     3. Identify related code: bash(grep -r "import.*${basename(file)}" ${workflowDir}/src --include="*.ts")
     4. Read test files: bash(find ${workflowDir}/tests -name "*${basename(file, '.ts')}*" -type f)
-    5. Execute: cat ~/.ccw/workflows/cli-templates/schemas/review-deep-dive-results-schema.json (get output schema reference)
+    5. Execute: ccw tool exec json_builder '{"cmd":"info","schema":"review-deep"}' (get output schema summary)
     6. Read: .workflow/project-tech.json (technology stack and architecture context)
     7. Read: .workflow/specs/*.md (user-defined constraints for remediation compliance)
 
@@ -550,7 +550,7 @@ Task(
        - Impact assessment and rollback strategy
 
     ## Success Criteria
-    - [ ] Schema obtained via cat review-deep-dive-results-schema.json
+    - [ ] Schema obtained via json_builder info
     - [ ] Root cause clearly identified with supporting evidence
     - [ ] Remediation plan is step-by-step actionable with exact file:line references
     - [ ] Each step includes specific commands and validation tests
diff --git a/.claude/skills/workflow-multi-cli-plan/SKILL.md b/.claude/skills/workflow-multi-cli-plan/SKILL.md
index d95d9c48..39bdf984 100644
--- a/.claude/skills/workflow-multi-cli-plan/SKILL.md
+++ b/.claude/skills/workflow-multi-cli-plan/SKILL.md
@@ -246,8 +246,8 @@ Agent({
   description: "Generate implementation plan",
   prompt: `
 ## Schema Reference
-Execute: cat ~/.ccw/workflows/cli-templates/schemas/plan-overview-base-schema.json
-Execute: cat ~/.ccw/workflows/cli-templates/schemas/task-schema.json
+Execute: ccw tool exec json_builder '{"cmd":"info","schema":"plan"}'
+Execute: ccw tool exec json_builder '{"cmd":"info","schema":"task"}'
 
 ## Output Format: Two-Layer Structure
 - plan.json: Overview with task_ids[] referencing .task/ files (NO tasks[] array)
diff --git a/.claude/skills/workflow-plan/phases/03-conflict-resolution.md b/.claude/skills/workflow-plan/phases/03-conflict-resolution.md
index 47b2c649..0a3eb94b 100644
--- a/.claude/skills/workflow-plan/phases/03-conflict-resolution.md
+++ b/.claude/skills/workflow-plan/phases/03-conflict-resolution.md
@@ -70,7 +70,7 @@ Task(subagent_type="cli-execution-agent", run_in_background=false, prompt=`
   ## Analysis Steps
 
   ### 0. Load Output Schema (MANDATORY)
-  Execute: cat ~/.ccw/workflows/cli-templates/schemas/conflict-resolution-schema.json
+  Execute: ccw tool exec json_builder '{"cmd":"info","schema":"conflict"}' (get schema summary)
 
   ### 1. Load Context
   - Read existing files from conflict_detection.existing_files
@@ -119,7 +119,7 @@ Task(subagent_type="cli-execution-agent", run_in_background=false, prompt=`
 
   Output to conflict-resolution.json (generated in Phase 4)
 
-  **Schema Reference**: Execute cat ~/.ccw/workflows/cli-templates/schemas/conflict-resolution-schema.json to get full schema
+  **Schema Reference**: Execute ccw tool exec json_builder '{"cmd":"info","schema":"conflict"}' to get schema summary
 
   Return JSON following the schema. Key requirements:
   - Minimum 2 strategies per conflict, max 4
diff --git a/.claude/skills/workflow-plan/phases/05-plan-verify.md b/.claude/skills/workflow-plan/phases/05-plan-verify.md
index 709d34ab..6e6a6860 100644
--- a/.claude/skills/workflow-plan/phases/05-plan-verify.md
+++ b/.claude/skills/workflow-plan/phases/05-plan-verify.md
@@ -195,8 +195,8 @@ Task(
 ## Plan Verification Task
 
 ### MANDATORY FIRST STEPS
-1. Read: ~/.ccw/workflows/cli-templates/schemas/plan-verify-agent-schema.json (dimensions & rules)
-2. Read: ~/.ccw/workflows/cli-templates/schemas/verify-json-schema.json (output schema)
+1. Execute: ccw tool exec json_builder '{"cmd":"info","schema":"plan-verify"}' (dimensions & rules)
+2. Execute: ccw tool exec json_builder '{"cmd":"info","schema":"verify"}' (output schema)
 3. Read: ${session_file} (user intent)
 4. Read: ${PLANNING_NOTES} (constraints & N+1 context)
 5. Read: ${IMPL_PLAN} (implementation plan)
diff --git a/.claude/skills/workflow-tdd-plan/phases/02-context-gathering.md b/.claude/skills/workflow-tdd-plan/phases/02-context-gathering.md
index 23f6759a..e1c2464c 100644
--- a/.claude/skills/workflow-tdd-plan/phases/02-context-gathering.md
+++ b/.claude/skills/workflow-tdd-plan/phases/02-context-gathering.md
@@ -99,7 +99,7 @@ Execute **${angle}** exploration for TDD task planning context. Analyze codebase
 ## MANDATORY FIRST STEPS (Execute by Agent)
 1. Run: ccw tool exec get_modules_by_depth '{}' (project structure)
 2. Run: rg -l "{keyword_from_task}" --type ts (locate relevant files)
-3. Execute: cat ~/.ccw/workflows/cli-templates/schemas/explore-json-schema.json (get output schema reference)
+3. Execute: ccw tool exec json_builder '{"cmd":"init","schema":"explore","output":"${sessionFolder}/exploration-${angle}.json"}' (init output + get schema info)
 
 ## Exploration Strategy (${angle} focus)
 
@@ -121,7 +121,7 @@ Execute **${angle}** exploration for TDD task planning context. Analyze codebase
 
 **File**: ${sessionFolder}/exploration-${angle}.json
 
-**Schema Reference**: Schema obtained in MANDATORY FIRST STEPS step 3, follow schema exactly
+**Schema Reference**: Skeleton initialized via json_builder in step 3. Use `set` to populate fields, `validate` before returning.
 
 **Required Fields** (all ${angle} focused):
 - project_structure: Modules/architecture relevant to ${angle}
@@ -141,7 +141,7 @@ Execute **${angle}** exploration for TDD task planning context. Analyze codebase
 - _metadata.exploration_angle: "${angle}"
 
 ## Success Criteria
-- [ ] Schema obtained via cat explore-json-schema.json
+- [ ] Schema initialized via json_builder init
 - [ ] get_modules_by_depth.sh executed
 - [ ] At least 3 relevant files identified with ${angle} rationale
 - [ ] Patterns are actionable (code examples, not generic advice)
diff --git a/.claude/skills/workflow-tdd-plan/phases/04-conflict-resolution.md b/.claude/skills/workflow-tdd-plan/phases/04-conflict-resolution.md
index 4cada932..da839c2b 100644
--- a/.claude/skills/workflow-tdd-plan/phases/04-conflict-resolution.md
+++ b/.claude/skills/workflow-tdd-plan/phases/04-conflict-resolution.md
@@ -70,7 +70,7 @@ Task(subagent_type="cli-execution-agent", run_in_background=false, prompt=`
   ## Analysis Steps
 
   ### 0. Load Output Schema (MANDATORY)
-  Execute: cat ~/.ccw/workflows/cli-templates/schemas/conflict-resolution-schema.json
+  Execute: ccw tool exec json_builder '{"cmd":"info","schema":"conflict"}'
 
   ### 1. Load Context
   - Read existing files from conflict_detection.existing_files
@@ -119,7 +119,7 @@ Task(subagent_type="cli-execution-agent", run_in_background=false, prompt=`
 
   Output to conflict-resolution.json (generated in Phase 4)
 
-  **Schema Reference**: Execute cat ~/.ccw/workflows/cli-templates/schemas/conflict-resolution-schema.json to get full schema
+  **Schema Reference**: Execute ccw tool exec json_builder '{"cmd":"info","schema":"conflict"}' to get schema summary
 
   Return JSON following the schema. Key requirements:
   - Minimum 2 strategies per conflict, max 4
diff --git a/.claude/skills/workflow-test-fix/phases/02-test-context-gather.md b/.claude/skills/workflow-test-fix/phases/02-test-context-gather.md
index 14903c75..55463932 100644
--- a/.claude/skills/workflow-test-fix/phases/02-test-context-gather.md
+++ b/.claude/skills/workflow-test-fix/phases/02-test-context-gather.md
@@ -223,7 +223,7 @@ Execute **${angle}** exploration for task planning context. Analyze codebase fro
 ## MANDATORY FIRST STEPS (Execute by Agent)
 1. Run: ccw tool exec get_modules_by_depth '{}' (project structure)
 2. Run: rg -l "{keyword_from_task}" --type ts (locate relevant files)
-3. Execute: cat ~/.ccw/workflows/cli-templates/schemas/explore-json-schema.json (get output schema reference)
+3. Execute: ccw tool exec json_builder '{"cmd":"init","schema":"explore","output":"${sessionFolder}/exploration-${angle}.json"}' (init output + get schema info)
 
 ## Exploration Strategy (${angle} focus)
 
@@ -265,7 +265,7 @@ Execute **${angle}** exploration for task planning context. Analyze codebase fro
 - _metadata.exploration_angle: "${angle}"
 
 ## Success Criteria
-- [ ] Schema obtained via cat explore-json-schema.json
+- [ ] Schema initialized via json_builder init
 - [ ] get_modules_by_depth.sh executed
 - [ ] At least 3 relevant files identified with ${angle} rationale
 - [ ] Patterns are actionable (code examples, not generic advice)
diff --git a/ccw/src/tools/index.ts b/ccw/src/tools/index.ts
index b0c4c4d1..a74f8d83 100644
--- a/ccw/src/tools/index.ts
+++ b/ccw/src/tools/index.ts
@@ -27,6 +27,7 @@ import * as contextCacheMod from './context-cache.js';
 import * as skillContextLoaderMod from './skill-context-loader.js';
 import * as askQuestionMod from './ask-question.js';
 import * as teamMsgMod from './team-msg.js';
+import * as jsonBuilderMod from './json-builder.js';
 
 
 // Import legacy JS tools
@@ -315,6 +316,7 @@ registerTool(toLegacyTool(contextCacheMod));
 registerTool(toLegacyTool(skillContextLoaderMod));
 registerTool(toLegacyTool(askQuestionMod));
 registerTool(toLegacyTool(teamMsgMod));
+registerTool(toLegacyTool(jsonBuilderMod));
 
 // Register legacy JS tools
 registerTool(uiGeneratePreviewTool);
diff --git a/ccw/src/tools/json-builder.ts b/ccw/src/tools/json-builder.ts
new file mode 100644
index 00000000..f9ac020d
--- /dev/null
+++ b/ccw/src/tools/json-builder.ts
@@ -0,0 +1,836 @@
+/**
+ * JSON Builder Tool - Schema-aware structured JSON construction/validation.
+ *
+ * Commands:
+ *   init     — Create empty schema-compliant JSON skeleton
+ *   set      — Set/append fields with instant validation
+ *   validate — Full schema + semantic validation
+ *   merge    — Merge multiple same-schema JSONs
+ *   info     — Get schema summary (replaces agent reading raw schema)
+ *
+ * Replaces agent hand-writing JSON + self-validation with tool-assisted
+ * incremental build + automatic validation.
+ */
+
+import { z } from 'zod';
+import type { ToolSchema, ToolResult } from '../types/tool.js';
+import { readFileSync, writeFileSync, existsSync, mkdirSync } from 'fs';
+import { resolve, dirname } from 'path';
+import { validatePath } from '../utils/path-validator.js';
+import {
+  loadSchema,
+  getSchemaInfo,
+  listSchemas,
+  type JsonSchema,
+  type JsonSchemaProperty,
+} from './schema-registry.js';
+
+// ─── Params ──────────────────────────────────────────────────
+
+const OpSchema = z.object({
+  path: z.string().min(1),
+  value: z.unknown(),
+});
+
+const ParamsSchema = z.object({
+  cmd: z.enum(['init', 'set', 'validate', 'merge', 'info']),
+  schema: z.string().optional(),
+  target: z.string().optional(),
+  output: z.string().optional(),
+  ops: z.array(OpSchema).optional(),
+  sources: z.array(z.string()).optional(),
+  strategy: z.string().optional(),
+});
+
+type Params = z.infer<typeof ParamsSchema>;
+
+// ─── Tool Schema ─────────────────────────────────────────────
+
+export const schema: ToolSchema = {
+  name: 'json_builder',
+  description: `Schema-aware JSON builder with validation. Commands:
+  init: Create skeleton from schema. Params: schema (string), output (string)
+  set: Set/append fields. Params: target (string), ops [{path, value}...]
+  validate: Full validation. Params: target (string), schema? (string)
+  merge: Merge JSONs. Params: sources (string[]), output (string), strategy? (string)
+  info: Schema summary. Params: schema (string)`,
+  inputSchema: {
+    type: 'object',
+    properties: {
+      cmd: { type: 'string', description: 'Command: init|set|validate|merge|info' },
+      schema: { type: 'string', description: 'Schema ID (e.g. explore, task, diagnosis)' },
+      target: { type: 'string', description: 'Target JSON file path' },
+      output: { type: 'string', description: 'Output file path' },
+      ops: {
+        type: 'array',
+        description: 'Set operations: [{path: "field.sub" or "arr[+]", value: ...}]',
+      },
+      sources: { type: 'array', description: 'Source files for merge' },
+      strategy: { type: 'string', description: 'Merge strategy: dedup_by_path (default)' },
+    },
+    required: ['cmd'],
+  },
+};
+
+// ─── Handler ─────────────────────────────────────────────────
+
+export async function handler(params: Record<string, unknown>): Promise<ToolResult> {
+  const parsed = ParamsSchema.safeParse(params);
+  if (!parsed.success) {
+    return { success: false, error: `Invalid params: ${parsed.error.message}` };
+  }
+
+  const p = parsed.data;
+  try {
+    switch (p.cmd) {
+      case 'init':    return await cmdInit(p);
+      case 'set':     return await cmdSet(p);
+      case 'validate':return await cmdValidate(p);
+      case 'merge':   return await cmdMerge(p);
+      case 'info':    return cmdInfo(p);
+      default:
+        return { success: false, error: `Unknown command: ${p.cmd}` };
+    }
+  } catch (err) {
+    return { success: false, error: (err as Error).message };
+  }
+}
+
+// ─── init ────────────────────────────────────────────────────
+
+async function cmdInit(p: Params): Promise<ToolResult> {
+  if (!p.schema) return { success: false, error: 'schema is required for init' };
+  if (!p.output) return { success: false, error: 'output is required for init' };
+
+  const jsonSchema = loadSchema(p.schema);
+  const skeleton = buildSkeleton(jsonSchema);
+  const outputPath = await validatePath(p.output);
+  ensureDir(outputPath);
+  const content = JSON.stringify(skeleton, null, 2);
+  writeFileSync(outputPath, content, 'utf-8');
+
+  const info = getSchemaInfo(p.schema);
+  return {
+    success: true,
+    result: {
+      path: outputPath,
+      schema: p.schema,
+      requiredFields: info.requiredFields,
+      arrayFields: info.arrayFields,
+      message: `Initialized ${p.schema} skeleton (${info.requiredFields.length} required fields)`,
+    },
+  };
+}
+
+/**
+ * Build a JSON skeleton from schema — fills required fields with type-appropriate defaults
+ */
+function buildSkeleton(schema: JsonSchema): Record<string, unknown> {
+  const result: Record<string, unknown> = {};
+  const props = schema.properties || {};
+  const required = new Set(schema.required || []);
+
+  for (const [name, prop] of Object.entries(props)) {
+    if (name.startsWith('_comment') || name.startsWith('$')) continue;
+    if (name === 'deprecated' || name === 'deprecated_message' || name === 'migration_guide') continue;
+    if (name === '_field_usage_by_producer' || name === '_directory_convention') continue;
+
+    // Only include required fields in skeleton
+    if (!required.has(name)) continue;
+
+    result[name] = getDefaultValue(prop);
+  }
+
+  return result;
+}
+
+function getDefaultValue(prop: JsonSchemaProperty): unknown {
+  if (prop.default !== undefined) return prop.default;
+
+  const type = Array.isArray(prop.type) ? prop.type[0] : prop.type;
+  switch (type) {
+    case 'string':  return '';
+    case 'number':
+    case 'integer': return 0;
+    case 'boolean': return false;
+    case 'array':   return [];
+    case 'object': {
+      if (!prop.properties) return {};
+      const obj: Record<string, unknown> = {};
+      const reqSet = new Set(prop.required || []);
+      for (const [k, v] of Object.entries(prop.properties)) {
+        if (reqSet.has(k)) {
+          obj[k] = getDefaultValue(v);
+        }
+      }
+      return obj;
+    }
+    default: return null;
+  }
+}
+
+// ─── set ─────────────────────────────────────────────────────
+
+async function cmdSet(p: Params): Promise<ToolResult> {
+  if (!p.target) return { success: false, error: 'target is required for set' };
+  if (!p.ops || p.ops.length === 0) return { success: false, error: 'ops is required for set' };
+
+  const targetPath = await validatePath(p.target);
+  if (!existsSync(targetPath)) {
+    return { success: false, error: `Target file not found: ${targetPath}` };
+  }
+
+  const raw = readFileSync(targetPath, 'utf-8');
+  const doc = JSON.parse(raw) as Record<string, unknown>;
+
+  // Detect schema from doc._metadata?.source or from file name
+  const schemaId = p.schema || detectSchema(doc, targetPath);
+
+  const errors: string[] = [];
+  const warnings: string[] = [];
+  let applied = 0;
+
+  for (const op of p.ops) {
+    const result = applyOp(doc, op.path, op.value, schemaId);
+    if (result.error) {
+      errors.push(`${op.path}: ${result.error}`);
+    } else {
+      applied++;
+      if (result.warnings) warnings.push(...result.warnings);
+    }
+  }
+
+  if (errors.length > 0 && applied === 0) {
+    return { success: false, error: `All ops failed: ${errors.join('; ')}` };
+  }
+
+  // Write back
+  writeFileSync(targetPath, JSON.stringify(doc, null, 2), 'utf-8');
+
+  return {
+    success: true,
+    result: { applied, errors, warnings },
+  };
+}
+
+interface OpResult {
+  error?: string;
+  warnings?: string[];
+}
+
+function applyOp(doc: Record<string, unknown>, path: string, value: unknown, schemaId?: string): OpResult {
+  const warnings: string[] = [];
+
+  // Handle "auto" values
+  if (value === 'auto') {
+    if (path.endsWith('timestamp')) {
+      value = new Date().toISOString();
+    }
+  }
+
+  // Parse path: "field.sub", "arr[+]", "arr[0]", "arr[?key=val]"
+  const segments = parsePath(path);
+  if (!segments || segments.length === 0) {
+    return { error: 'Invalid path syntax' };
+  }
+
+  // Validate value against schema if schema is known
+  if (schemaId) {
+    const validationResult = validateFieldValue(schemaId, path, value);
+    if (validationResult.error) return { error: validationResult.error };
+    if (validationResult.warnings) warnings.push(...validationResult.warnings);
+  }
+
+  // Navigate to parent and set
+  let current: unknown = doc;
+  for (let i = 0; i < segments.length - 1; i++) {
+    const seg = segments[i];
+    if (seg.type === 'key') {
+      if (typeof current !== 'object' || current === null) {
+        return { error: `Cannot navigate into non-object at "${seg.value}"` };
+      }
+      const obj = current as Record<string, unknown>;
+      if (obj[seg.value] === undefined) {
+        // Auto-create intermediate objects/arrays
+        const nextSeg = segments[i + 1];
+        obj[seg.value] = nextSeg.type === 'append' || nextSeg.type === 'index' ? [] : {};
+      }
+      current = obj[seg.value];
+    } else if (seg.type === 'index') {
+      if (!Array.isArray(current)) return { error: `Not an array at index ${seg.value}` };
+      current = current[Number(seg.value)];
+    }
+  }
+
+  // Apply final segment
+  const last = segments[segments.length - 1];
+  if (last.type === 'key') {
+    if (typeof current !== 'object' || current === null || Array.isArray(current)) {
+      return { error: `Cannot set key "${last.value}" on non-object` };
+    }
+    (current as Record<string, unknown>)[last.value] = value;
+  } else if (last.type === 'append') {
+    if (!Array.isArray(current)) {
+      return { error: `Cannot append to non-array` };
+    }
+    current.push(value);
+  } else if (last.type === 'index') {
+    if (!Array.isArray(current)) {
+      return { error: `Cannot index into non-array` };
+    }
+    current[Number(last.value)] = value;
+  } else if (last.type === 'query') {
+    if (!Array.isArray(current)) {
+      return { error: `Cannot query non-array` };
+    }
+    const { key, val } = last as QuerySegment;
+    const idx = current.findIndex((item: unknown) =>
+      typeof item === 'object' && item !== null && (item as Record<string, unknown>)[key] === val
+    );
+    if (idx === -1) return { error: `No item found where ${key}=${val}` };
+    current[idx] = value;
+  }
+
+  return { warnings: warnings.length > 0 ? warnings : undefined };
+}
+
+interface KeySegment { type: 'key'; value: string; }
+interface IndexSegment { type: 'index'; value: string; }
+interface AppendSegment { type: 'append'; value: string; }
+interface QuerySegment { type: 'query'; value: string; key: string; val: string; }
+type PathSegment = KeySegment | IndexSegment | AppendSegment | QuerySegment;
+
+function parsePath(path: string): PathSegment[] | null {
+  const segments: PathSegment[] = [];
+  // Split by '.' but respect brackets
+  const parts = path.split(/\.(?![^\[]*\])/);
+
+  for (const part of parts) {
+    const bracketMatch = part.match(/^(\w+)\[(.+)\]$/);
+    if (bracketMatch) {
+      const [, field, bracket] = bracketMatch;
+      segments.push({ type: 'key', value: field });
+
+      if (bracket === '+') {
+        segments.push({ type: 'append', value: '+' });
+      } else if (/^\d+$/.test(bracket)) {
+        segments.push({ type: 'index', value: bracket });
+      } else if (bracket.includes('=')) {
+        const [key, val] = bracket.split('=', 2);
+        segments.push({ type: 'query', value: bracket, key: key.replace('?', ''), val } as QuerySegment);
+      }
+    } else {
+      segments.push({ type: 'key', value: part });
+    }
+  }
+
+  return segments.length > 0 ? segments : null;
+}
+
+// ─── validate ────────────────────────────────────────────────
+
+async function cmdValidate(p: Params): Promise<ToolResult> {
+  if (!p.target) return { success: false, error: 'target is required for validate' };
+
+  const targetPath = await validatePath(p.target);
+  if (!existsSync(targetPath)) {
+    return { success: false, error: `Target file not found: ${targetPath}` };
+  }
+
+  const raw = readFileSync(targetPath, 'utf-8');
+  let doc: Record<string, unknown>;
+  try {
+    doc = JSON.parse(raw);
+  } catch {
+    return { success: false, error: 'Invalid JSON in target file' };
+  }
+
+  const schemaId = p.schema || detectSchema(doc, targetPath);
+  if (!schemaId) {
+    return { success: false, error: 'Cannot detect schema. Provide schema param.' };
+  }
+
+  const jsonSchema = loadSchema(schemaId);
+  const errors: string[] = [];
+  const warnings: string[] = [];
+
+  // Layer 1: JSON Schema structural validation
+  validateObject(doc, jsonSchema, '', errors, warnings);
+
+  // Layer 2: Semantic quality validation
+  validateSemantics(doc, schemaId, errors, warnings);
+
+  const stats = {
+    fields: Object.keys(doc).filter(k => !k.startsWith('_comment')).length,
+    schema: schemaId,
+    arrayItems: countArrayItems(doc, jsonSchema),
+  };
+
+  return {
+    success: true,
+    result: {
+      valid: errors.length === 0,
+      errors,
+      warnings,
+      stats,
+    },
+  };
+}
+
+function validateObject(
+  obj: Record<string, unknown>,
+  schema: JsonSchema | JsonSchemaProperty,
+  prefix: string,
+  errors: string[],
+  warnings: string[],
+): void {
+  const props = schema.properties || {};
+  const required = new Set(schema.required || []);
+
+  // Check required fields
+  for (const req of required) {
+    const val = obj[req];
+    if (val === undefined || val === null) {
+      errors.push(`${prefix}${req}: required field missing`);
+    } else if (typeof val === 'string' && val === '' && req !== 'error_message') {
+      errors.push(`${prefix}${req}: required field is empty string`);
+    } else if (Array.isArray(val) && val.length === 0) {
+      const propSchema = props[req];
+      if (propSchema?.minItems && propSchema.minItems > 0) {
+        errors.push(`${prefix}${req}: array requires at least ${propSchema.minItems} items`);
+      }
+    }
+  }
+
+  // Validate each field
+  for (const [name, value] of Object.entries(obj)) {
+    if (name.startsWith('_comment') || name.startsWith('$')) continue;
+    const propSchema = props[name];
+    if (!propSchema) continue; // allow additional props
+
+    validateValue(value, propSchema, `${prefix}${name}`, errors, warnings);
+  }
+}
+
+function validateValue(
+  value: unknown,
+  propSchema: JsonSchemaProperty,
+  path: string,
+  errors: string[],
+  warnings: string[],
+): void {
+  if (value === null || value === undefined) return;
+
+  const expectedType = Array.isArray(propSchema.type) ? propSchema.type : [propSchema.type];
+
+  // Type check
+  const actualType = Array.isArray(value) ? 'array' : typeof value;
+  if (propSchema.type && !expectedType.includes(actualType) && !expectedType.includes('null')) {
+    // integer is typeof 'number'
+    if (!(actualType === 'number' && expectedType.includes('integer'))) {
+      errors.push(`${path}: expected ${expectedType.join('|')}, got ${actualType}`);
+      return;
+    }
+  }
+
+  // Enum check
+  if (propSchema.enum && !propSchema.enum.includes(value as string | number)) {
+    errors.push(`${path}: value "${value}" not in enum [${propSchema.enum.join(', ')}]`);
+  }
+
+  // Const check
+  if (propSchema.const !== undefined && value !== propSchema.const) {
+    errors.push(`${path}: expected const "${propSchema.const}", got "${value}"`);
+  }
+
+  // String constraints
+  if (typeof value === 'string') {
+    if (propSchema.minLength && value.length < propSchema.minLength) {
+      errors.push(`${path}: string length ${value.length} < minLength ${propSchema.minLength}`);
+    }
+    if (propSchema.maxLength && value.length > propSchema.maxLength) {
+      errors.push(`${path}: string length ${value.length} > maxLength ${propSchema.maxLength}`);
+    }
+    if (propSchema.pattern) {
+      try {
+        if (!new RegExp(propSchema.pattern).test(value)) {
+          errors.push(`${path}: does not match pattern "${propSchema.pattern}"`);
+        }
+      } catch { /* skip invalid regex in schema */ }
+    }
+  }
+
+  // Number constraints
+  if (typeof value === 'number') {
+    if (propSchema.minimum !== undefined && value < propSchema.minimum) {
+      errors.push(`${path}: ${value} < minimum ${propSchema.minimum}`);
+    }
+    if (propSchema.maximum !== undefined && value > propSchema.maximum) {
+      errors.push(`${path}: ${value} > maximum ${propSchema.maximum}`);
+    }
+  }
+
+  // Array constraints
+  if (Array.isArray(value)) {
+    if (propSchema.minItems && value.length < propSchema.minItems) {
+      errors.push(`${path}: array has ${value.length} items, needs >= ${propSchema.minItems}`);
+    }
+    if (propSchema.maxItems && value.length > propSchema.maxItems) {
+      warnings.push(`${path}: array has ${value.length} items, max recommended ${propSchema.maxItems}`);
+    }
+    // Validate each item
+    if (propSchema.items && typeof propSchema.items === 'object') {
+      for (let i = 0; i < value.length; i++) {
+        const item = value[i];
+        if (propSchema.items.type === 'object' && typeof item === 'object' && item !== null) {
+          validateObject(item as Record<string, unknown>, propSchema.items, `${path}[${i}].`, errors, warnings);
+        } else {
+          validateValue(item, propSchema.items, `${path}[${i}]`, errors, warnings);
+        }
+      }
+    }
+  }
+
+  // Object: recurse
+  if (typeof value === 'object' && !Array.isArray(value) && value !== null && propSchema.properties) {
+    validateObject(value as Record<string, unknown>, propSchema, `${path}.`, errors, warnings);
+  }
+}
+
+// ─── Semantic Validation (Layer 2) ───────────────────────────
+
+function validateSemantics(doc: Record<string, unknown>, schemaId: string, errors: string[], warnings: string[]): void {
+  // explore + diagnosis: file list quality
+  if (schemaId === 'explore') {
+    validateFileList(doc, 'relevant_files', errors, warnings);
+  } else if (schemaId === 'diagnosis') {
+    validateFileList(doc, 'affected_files', errors, warnings);
+  }
+
+  // task: circular dependency check
+  if (schemaId === 'task' || schemaId === 'solution' || schemaId === 'plan' || schemaId === 'plan-legacy') {
+    validateNoCyclicDeps(doc, errors);
+  }
+}
+
+const GENERIC_PHRASES = [
+  'related to', 'relevant file', 'relevant to', 'important file',
+  'related file', 'useful for', 'needed for',
+];
+
+function validateFileList(doc: Record<string, unknown>, field: string, errors: string[], warnings: string[]): void {
+  const files = doc[field];
+  if (!Array.isArray(files)) return;
+
+  const allManual = files.length > 0 && files.every((f: Record<string, unknown>) => f.discovery_source === 'manual');
+  if (allManual && files.length > 3) {
+    warnings.push(`${field}: all ${files.length} files discovered via "manual" — consider using bash-scan or cli-analysis`);
+  }
+
+  for (let i = 0; i < files.length; i++) {
+    const f = files[i] as Record<string, unknown>;
+    const rationale = (f.rationale as string) || '';
+    const relevance = (f.relevance as number) || 0;
+
+    // Check generic rationale
+    const lower = rationale.toLowerCase();
+    for (const phrase of GENERIC_PHRASES) {
+      if (lower === phrase || (lower.length < 25 && lower.includes(phrase))) {
+        warnings.push(`${field}[${i}].rationale: too generic ("${rationale}") — be more specific`);
+        break;
+      }
+    }
+
+    // High relevance files need key_code and topic_relation
+    if (relevance >= 0.7) {
+      if (!f.key_code || (Array.isArray(f.key_code) && (f.key_code as unknown[]).length === 0)) {
+        warnings.push(`${field}[${i}]: relevance=${relevance} but missing key_code (recommended for >= 0.7)`);
+      }
+      if (!f.topic_relation) {
+        warnings.push(`${field}[${i}]: relevance=${relevance} but missing topic_relation (recommended for >= 0.7)`);
+      }
+    }
+  }
+}
+
+function validateNoCyclicDeps(doc: Record<string, unknown>, errors: string[]): void {
+  const tasks = (doc.tasks as Array<Record<string, unknown>>) || [];
+  if (tasks.length === 0) return;
+
+  // Build adjacency
+  const deps = new Map<string, string[]>();
+  for (const t of tasks) {
+    const id = t.id as string;
+    if (!id) continue;
+    deps.set(id, (t.depends_on as string[]) || []);
+  }
+
+  // DFS cycle check
+  const visited = new Set<string>();
+  const stack = new Set<string>();
+
+  function hasCycle(node: string): boolean {
+    if (stack.has(node)) return true;
+    if (visited.has(node)) return false;
+    visited.add(node);
+    stack.add(node);
+    for (const dep of deps.get(node) || []) {
+      if (hasCycle(dep)) return true;
+    }
+    stack.delete(node);
+    return false;
+  }
+
+  for (const id of deps.keys()) {
+    if (hasCycle(id)) {
+      errors.push(`tasks: circular dependency detected involving "${id}"`);
+      break;
+    }
+  }
+}
+
+function countArrayItems(doc: Record<string, unknown>, schema: JsonSchema): Record<string, number> {
+  const counts: Record<string, number> = {};
+  for (const [name, value] of Object.entries(doc)) {
+    if (Array.isArray(value)) {
+      counts[name] = value.length;
+    }
+  }
+  return counts;
+}
+
+// ─── Field-level validation (for set) ────────────────────────
+
+interface FieldValidation {
+  error?: string;
+  warnings?: string[];
+}
+
+function validateFieldValue(schemaId: string, fieldPath: string, value: unknown): FieldValidation {
+  const warnings: string[] = [];
+  let jsonSchema: JsonSchema;
+  try {
+    jsonSchema = loadSchema(schemaId);
+  } catch {
+    return {}; // Skip validation if schema not found
+  }
+
+  // Resolve the property schema for this path
+  const propSchema = resolvePropertySchema(jsonSchema, fieldPath);
+  if (!propSchema) return {}; // Unknown field, allow it
+
+  // For array appends, validate the item against items schema
+  if (fieldPath.includes('[+]') || fieldPath.match(/\[\d+\]/)) {
+    const itemSchema = propSchema.items;
+    if (itemSchema && typeof value === 'object' && value !== null) {
+      const errors: string[] = [];
+      if (itemSchema.type === 'object') {
+        validateObject(value as Record<string, unknown>, itemSchema, '', errors, warnings);
+      }
+      if (errors.length > 0) return { error: errors.join('; ') };
+    }
+    return { warnings: warnings.length > 0 ? warnings : undefined };
+  }
+
+  // For direct field set, validate the value
+  const errors: string[] = [];
+  validateValue(value, propSchema, fieldPath, errors, warnings);
+  if (errors.length > 0) return { error: errors.join('; ') };
+  return { warnings: warnings.length > 0 ? warnings : undefined };
+}
+
+function resolvePropertySchema(schema: JsonSchema, fieldPath: string): JsonSchemaProperty | null {
+  const cleanPath = fieldPath.replace(/\[\+\]|\[\d+\]|\[\?[^\]]+\]/g, '');
+  const parts = cleanPath.split('.');
+  let current: JsonSchemaProperty | undefined = schema as unknown as JsonSchemaProperty;
+
+  for (const part of parts) {
+    if (!part) continue;
+    if (current?.properties?.[part]) {
+      current = current.properties[part];
+    } else if (current?.items?.properties?.[part]) {
+      current = current.items.properties[part];
+    } else {
+      return null;
+    }
+  }
+
+  return current || null;
+}
+
+// ─── merge ───────────────────────────────────────────────────
+
+async function cmdMerge(p: Params): Promise<ToolResult> {
+  if (!p.sources || p.sources.length < 2) {
+    return { success: false, error: 'merge requires at least 2 sources' };
+  }
+  if (!p.output) return { success: false, error: 'output is required for merge' };
+
+  const docs: Record<string, unknown>[] = [];
+  for (const src of p.sources) {
+    const srcPath = await validatePath(src);
+    if (!existsSync(srcPath)) {
+      return { success: false, error: `Source not found: ${srcPath}` };
+    }
+    docs.push(JSON.parse(readFileSync(srcPath, 'utf-8')));
+  }
+
+  const schemaId = p.schema || detectSchema(docs[0], p.sources[0]);
+  const jsonSchema = schemaId ? loadSchema(schemaId) : null;
+  const strategy = p.strategy || 'dedup_by_path';
+
+  const merged = mergeDocuments(docs, jsonSchema, strategy);
+
+  const outputPath = await validatePath(p.output);
+  ensureDir(outputPath);
+  writeFileSync(outputPath, JSON.stringify(merged, null, 2), 'utf-8');
+
+  return {
+    success: true,
+    result: {
+      path: outputPath,
+      sourceCount: docs.length,
+      strategy,
+      message: `Merged ${docs.length} documents`,
+    },
+  };
+}
+
+function mergeDocuments(
+  docs: Record<string, unknown>[],
+  schema: JsonSchema | null,
+  strategy: string,
+): Record<string, unknown> {
+  const base = structuredClone(docs[0]);
+  const props = schema?.properties || {};
+
+  for (let i = 1; i < docs.length; i++) {
+    const other = docs[i];
+    for (const [key, value] of Object.entries(other)) {
+      if (key.startsWith('_') || key.startsWith('$')) continue;
+
+      const existing = base[key];
+      const propSchema = props[key];
+      const propType = propSchema?.type;
+
+      if (Array.isArray(existing) && Array.isArray(value)) {
+        // Array merge with dedup
+        if (strategy === 'dedup_by_path') {
+          base[key] = deduplicateArrays(existing, value);
+        } else {
+          base[key] = [...existing, ...value];
+        }
+      } else if (typeof existing === 'string' && typeof value === 'string' && propType === 'string') {
+        // Text fields: concatenate if both non-empty
+        if (existing && value && existing !== value) {
+          base[key] = `${existing}\n\n${value}`;
+        } else if (!existing && value) {
+          base[key] = value;
+        }
+      } else if (existing === undefined || existing === null || existing === '' || existing === 0) {
+        // Fill empty values
+        base[key] = value;
+      }
+    }
+  }
+
+  // Update metadata
+  if (base._metadata && typeof base._metadata === 'object') {
+    (base._metadata as Record<string, unknown>).timestamp = new Date().toISOString();
+    (base._metadata as Record<string, unknown>).merged_from = docs.length;
+  }
+
+  return base;
+}
+
+function deduplicateArrays(a: unknown[], b: unknown[]): unknown[] {
+  const result = [...a];
+  const existingPaths = new Set(
+    a.filter(item => typeof item === 'object' && item !== null)
+      .map(item => (item as Record<string, unknown>).path as string)
+      .filter(Boolean)
+  );
+
+  for (const item of b) {
+    if (typeof item === 'object' && item !== null) {
+      const path = (item as Record<string, unknown>).path as string;
+      if (path && existingPaths.has(path)) {
+        // Dedup: keep the one with higher relevance
+        const existingIdx = result.findIndex(
+          e => typeof e === 'object' && e !== null && (e as Record<string, unknown>).path === path
+        );
+        if (existingIdx !== -1) {
+          const existingRel = ((result[existingIdx] as Record<string, unknown>).relevance as number) || 0;
+          const newRel = ((item as Record<string, unknown>).relevance as number) || 0;
+          if (newRel > existingRel) {
+            result[existingIdx] = item;
+          }
+        }
+      } else {
+        result.push(item);
+        if (path) existingPaths.add(path);
+      }
+    } else {
+      // Primitive: dedup by value
+      if (!result.includes(item)) {
+        result.push(item);
+      }
+    }
+  }
+
+  return result;
+}
+
+// ─── info ────────────────────────────────────────────────────
+
+function cmdInfo(p: Params): ToolResult {
+  if (!p.schema) {
+    // List all schemas
+    const schemas = listSchemas();
+    const summaries = schemas.map(id => {
+      try {
+        const info = getSchemaInfo(id);
+        return { id, title: info.title, required: info.requiredFields.length, format: info.format };
+      } catch {
+        return { id, title: '(load error)', required: 0, format: 'json' };
+      }
+    });
+    return { success: true, result: { schemas: summaries } };
+  }
+
+  const info = getSchemaInfo(p.schema);
+  return { success: true, result: info };
+}
+
+// ─── Utilities ───────────────────────────────────────────────
+
+function ensureDir(filePath: string): void {
+  const dir = dirname(filePath);
+  if (!existsSync(dir)) {
+    mkdirSync(dir, { recursive: true });
+  }
+}
+
+function detectSchema(doc: Record<string, unknown>, filePath: string): string | undefined {
+  // Try _metadata.source
+  const meta = doc._metadata as Record<string, unknown> | undefined;
+  if (meta?.source === 'cli-explore-agent') {
+    if (doc.symptom || doc.root_cause) return 'diagnosis';
+    return 'explore';
+  }
+
+  // Try file name patterns
+  const lower = (filePath || '').toLowerCase();
+  if (lower.includes('exploration') || lower.includes('explore')) return 'explore';
+  if (lower.includes('diagnosis') || lower.includes('diagnos')) return 'diagnosis';
+  if (lower.includes('finding') || lower.includes('discovery')) return 'finding';
+  if (lower.includes('fix-plan') || lower.includes('fixplan')) return 'fix-legacy';
+  if (lower.includes('plan')) return 'plan';
+  if (lower.includes('task') || lower.includes('impl-')) return 'task';
+  if (lower.includes('solution')) return 'solution';
+  if (lower.includes('queue')) return 'queue';
+  if (lower.includes('review-dim')) return 'review-dim';
+  if (lower.includes('review-deep')) return 'review-deep';
+
+  return undefined;
+}
diff --git a/ccw/src/tools/schema-registry.ts b/ccw/src/tools/schema-registry.ts
new file mode 100644
index 00000000..9bfc2f57
--- /dev/null
+++ b/ccw/src/tools/schema-registry.ts
@@ -0,0 +1,201 @@
+/**
+ * Schema Registry - Loads and caches JSON schemas from the schemas directory.
+ * Provides schema metadata extraction for json-builder tool.
+ */
+
+import { readFileSync, existsSync } from 'fs';
+import { resolve, dirname } from 'path';
+import { fileURLToPath } from 'url';
+
+export interface SchemaEntry {
+  id: string;
+  title: string;
+  file: string;
+  format: 'json' | 'jsonl' | 'ndjson';
+  /** Top-level array field names (for append operations) */
+  arrayFields: string[];
+}
+
+export interface SchemaInfo {
+  id: string;
+  title: string;
+  description: string;
+  requiredFields: string[];
+  optionalFields: string[];
+  arrayFields: string[];
+  enumFields: Record<string, string[]>;
+  format: string;
+}
+
+interface JsonSchema {
+  title?: string;
+  description?: string;
+  type?: string;
+  required?: string[];
+  properties?: Record<string, JsonSchemaProperty>;
+  items?: JsonSchemaProperty;
+  [key: string]: unknown;
+}
+
+interface JsonSchemaProperty {
+  type?: string | string[];
+  enum?: (string | number)[];
+  const?: unknown;
+  required?: string[];
+  properties?: Record<string, JsonSchemaProperty>;
+  items?: JsonSchemaProperty;
+  minLength?: number;
+  maxLength?: number;
+  minItems?: number;
+  maxItems?: number;
+  minimum?: number;
+  maximum?: number;
+  pattern?: string;
+  format?: string;
+  description?: string;
+  default?: unknown;
+  oneOf?: JsonSchemaProperty[];
+  anyOf?: JsonSchemaProperty[];
+  additionalProperties?: boolean | JsonSchemaProperty;
+  [key: string]: unknown;
+}
+
+// Schema definitions — maps short IDs to schema files
+const SCHEMA_DEFS: Record<string, Omit<SchemaEntry, 'id' | 'title'>> = {
+  'explore':      { file: 'explore-json-schema.json',              arrayFields: ['relevant_files', 'clarification_needs'], format: 'json' },
+  'diagnosis':    { file: 'diagnosis-json-schema.json',            arrayFields: ['affected_files', 'reproduction_steps', 'fix_hints', 'clarification_needs'], format: 'json' },
+  'finding':      { file: 'discovery-finding-schema.json',         arrayFields: ['findings', 'cross_references'], format: 'json' },
+  'plan':         { file: 'plan-overview-base-schema.json',        arrayFields: ['tasks', 'design_decisions', 'focus_paths'], format: 'json' },
+  'plan-fix':     { file: 'plan-overview-fix-schema.json',         arrayFields: ['tasks', 'focus_paths'], format: 'json' },
+  'plan-legacy':  { file: 'plan-json-schema.json',                 arrayFields: ['tasks', 'design_decisions', 'focus_paths'], format: 'json' },
+  'fix-legacy':   { file: 'fix-plan-json-schema.json',             arrayFields: ['tasks', 'focus_paths'], format: 'json' },
+  'tech':         { file: 'project-tech-schema.json',              arrayFields: [], format: 'json' },
+  'guidelines':   { file: 'project-guidelines-schema.json',        arrayFields: [], format: 'json' },
+  'issue':        { file: 'issues-jsonl-schema.json',              arrayFields: [], format: 'jsonl' },
+  'queue':        { file: 'queue-schema.json',                     arrayFields: ['entries'], format: 'json' },
+  'review-dim':   { file: 'review-dimension-results-schema.json',  arrayFields: ['results'], format: 'json' },
+  'review-deep':  { file: 'review-deep-dive-results-schema.json',  arrayFields: ['results'], format: 'json' },
+  'debug-log':    { file: 'debug-log-json-schema.json',            arrayFields: [], format: 'ndjson' },
+  'discussion':   { file: 'multi-cli-discussion-schema.json',      arrayFields: ['turns'], format: 'json' },
+  'task':         { file: 'task-schema.json',                      arrayFields: ['files', 'implementation', 'risks', 'pre_analysis', 'artifacts'], format: 'json' },
+  'solution':     { file: 'solution-schema.json',                  arrayFields: ['tasks'], format: 'json' },
+  'verify':       { file: 'verify-json-schema.json',               arrayFields: [], format: 'json' },
+  'discovery-state': { file: 'discovery-state-schema.json',        arrayFields: [], format: 'json' },
+  'conflict':     { file: 'conflict-resolution-schema.json',       arrayFields: [], format: 'json' },
+  'registry':     { file: 'registry-schema.json',                  arrayFields: [], format: 'json' },
+  'team-tasks':   { file: 'team-tasks-schema.json',                arrayFields: [], format: 'json' },
+  'plan-verify':  { file: 'plan-verify-agent-schema.json',         arrayFields: [], format: 'json' },
+};
+
+// Cache loaded schemas
+const schemaCache = new Map<string, JsonSchema>();
+
+/**
+ * Resolve the schemas directory path
+ */
+function getSchemasDir(): string {
+  // Try environment variable first
+  if (process.env.CCW_HOME) {
+    return resolve(process.env.CCW_HOME, 'workflows', 'cli-templates', 'schemas');
+  }
+  // Try home directory
+  const home = process.env.HOME || process.env.USERPROFILE || '';
+  const ccwDir = resolve(home, '.ccw', 'workflows', 'cli-templates', 'schemas');
+  if (existsSync(ccwDir)) return ccwDir;
+  // Fallback to relative from this file
+  const thisDir = dirname(fileURLToPath(import.meta.url));
+  return resolve(thisDir, '..', '..', '..', '.ccw', 'workflows', 'cli-templates', 'schemas');
+}
+
+/**
+ * Load a raw JSON schema by ID
+ */
+export function loadSchema(schemaId: string): JsonSchema {
+  const cached = schemaCache.get(schemaId);
+  if (cached) return cached;
+
+  const def = SCHEMA_DEFS[schemaId];
+  if (!def) {
+    throw new Error(`Unknown schema: "${schemaId}". Available: ${Object.keys(SCHEMA_DEFS).join(', ')}`);
+  }
+
+  const schemasDir = getSchemasDir();
+  const filePath = resolve(schemasDir, def.file);
+  if (!existsSync(filePath)) {
+    throw new Error(`Schema file not found: ${filePath}`);
+  }
+
+  const raw = readFileSync(filePath, 'utf-8');
+  const schema = JSON.parse(raw) as JsonSchema;
+  schemaCache.set(schemaId, schema);
+  return schema;
+}
+
+/**
+ * Get schema entry metadata (without loading full schema)
+ */
+export function getSchemaEntry(schemaId: string): SchemaEntry {
+  const def = SCHEMA_DEFS[schemaId];
+  if (!def) {
+    throw new Error(`Unknown schema: "${schemaId}". Available: ${Object.keys(SCHEMA_DEFS).join(', ')}`);
+  }
+  const schema = loadSchema(schemaId);
+  return { id: schemaId, title: schema.title || schemaId, ...def };
+}
+
+/**
+ * Get schema info summary (for agent consumption — replaces reading full schema)
+ */
+export function getSchemaInfo(schemaId: string): SchemaInfo {
+  const schema = loadSchema(schemaId);
+  const def = SCHEMA_DEFS[schemaId];
+  const props = schema.properties || {};
+  const required = schema.required || [];
+  const allFields = Object.keys(props).filter(k => !k.startsWith('_comment'));
+  const optional = allFields.filter(f => !required.includes(f));
+
+  const enumFields: Record<string, string[]> = {};
+  for (const [name, prop] of Object.entries(props)) {
+    if (name.startsWith('_comment')) continue;
+    if (prop.enum) {
+      enumFields[name] = prop.enum.map(String);
+    }
+    // Check nested enum in properties
+    if (prop.properties) {
+      for (const [sub, subProp] of Object.entries(prop.properties)) {
+        if (subProp.enum) {
+          enumFields[`${name}.${sub}`] = subProp.enum.map(String);
+        }
+      }
+    }
+    // Check items enum for array fields
+    if (prop.items && typeof prop.items === 'object' && prop.items.properties) {
+      for (const [sub, subProp] of Object.entries(prop.items.properties)) {
+        if (subProp.enum) {
+          enumFields[`${name}[].${sub}`] = subProp.enum.map(String);
+        }
+      }
+    }
+  }
+
+  return {
+    id: schemaId,
+    title: schema.title || schemaId,
+    description: schema.description || '',
+    requiredFields: required,
+    optionalFields: optional,
+    arrayFields: def.arrayFields,
+    enumFields,
+    format: def.format,
+  };
+}
+
+/**
+ * List all available schema IDs
+ */
+export function listSchemas(): string[] {
+  return Object.keys(SCHEMA_DEFS);
+}
+
+// Exports for validation
+export type { JsonSchema, JsonSchemaProperty };