# API Validate

> API contract validation and breaking change detection Use when this capability is needed.

- Skill: `tomevault-io/api-validate` (Agent Skill, multi-file: 2 files)
- Install (CLI): `npx skillmds@latest add tomevault-io/api-validate`
- Raw SKILL.md: https://api.skillmd.com/api/skills/tomevault-io/api-validate/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Integrations & APIs
- Author: tomevault-io (https://skillmd.com/u/tomevault-io)
- Updated: 2026-09-17
- Page: https://skillmd.com/skills/tomevault-io/api-validate

---


# API Contract Validation

I'll analyze your API contracts for breaking changes, compatibility issues, and schema validation.

Arguments: `$ARGUMENTS` - API spec paths, comparison targets, or validation focus

## Token Optimization Strategy

**Target Reduction: 50% (3,000-5,000 → 1,000-2,500 tokens)**

This skill uses aggressive optimization through checksum-based caching, schema diffing, and early exit patterns to minimize token usage while providing comprehensive API contract validation.

### Optimization Patterns Applied

1. **OpenAPI Schema Caching (60% reduction)**
   - Cache parsed OpenAPI/Swagger schemas with checksums
   - Detect changes via file checksums before expensive parsing
   - Reuse cached schemas across validations
   - Share contract cache with `/api-test-generate`, `/api-docs-generate`
   - **Pattern:** `SESSION-STATE` + `CHECKSUM-VALIDATION`

2. **Breaking Change Detection with Pattern Matching (70% reduction)**
   - Template-based breaking change rules (no LLM needed for common patterns)
   - Regex patterns for endpoint removal, type changes, required fields
   - Progressive disclosure: Show breaking changes first, details on demand
   - **Pattern:** `TEMPLATE-RULES` + `PROGRESSIVE-DISCLOSURE`

3. **Contract Diff Comparison (80% reduction)**
   - Compare schema diffs, not full API spec files
   - Endpoint-level comparison (only changed endpoints analyzed)
   - JSON path-based field diffing
   - **Pattern:** `DIFF-ONLY` + `INCREMENTAL`

4. **Endpoint Version Comparison (50% reduction)**
   - Compare version metadata first (quick version number check)
   - Skip unchanged endpoints (checksum per endpoint)
   - Batch endpoint analysis (process multiple endpoints in one pass)
   - **Pattern:** `BATCH-OPERATIONS` + `EARLY-EXIT`

5. **Git Diff for Changed API Specs Only (90% reduction)**
   - Use `git diff` to identify changed API spec files
   - Only validate modified specs since last baseline
   - Skip validation if no API specs changed
   - **Pattern:** `GIT-DIFF-DEFAULT` + `EARLY-EXIT`

6. **Template-Based Validation Rules (75% reduction)**
   - Pre-defined breaking change rules (field removal, type change, etc.)
   - Semantic versioning compliance templates
   - Standard backward compatibility checks
   - **Pattern:** `TEMPLATE-BASED` + `RULE-ENGINE`

### Token Usage by Validation Mode

| Mode | Scenario | Token Usage | Primary Optimization |
|------|----------|-------------|---------------------|
| Status Check | No changes detected | 200-500 | Git diff + Early exit (95% savings) |
| Baseline Validation | Compare against baseline | 1,000-2,000 | Schema diff + Caching (60% savings) |
| Create Baseline | Initial contract capture | 1,500-2,500 | Schema extraction + Caching (40% savings) |
| Version Compare | Compare specific versions | 2,000-3,000 | Endpoint comparison + Progressive disclosure (50% savings) |
| Full Analysis | Comprehensive validation | 2,000-2,500 | All patterns combined (50% savings) |

### Caching Architecture

**Session Files (Project Root):**
```
api-validate/
├── baseline.json          # Contract baseline with checksums
├── state.json            # Validation state and metadata
├── plan.md               # Validation plan and findings
└── endpoints.json        # Cached endpoint schemas
```

**Shared Cache (Claude Code Cache):**
```
.claude/cache/api/
├── contracts.json        # Shared contract cache
├── schemas/              # Parsed OpenAPI schemas
│   ├── {checksum}.json  # Schema by file checksum
│   └── metadata.json    # Schema metadata
└── validation-rules.json # Breaking change templates
```

**Cache Strategy:**
- **Schema Cache:** Valid until API spec file checksum changes
- **Endpoint Cache:** Per-endpoint checksums for granular invalidation
- **Validation Rules:** Static templates, never expire
- **Baseline Cache:** Valid until explicit baseline update
- **Shared Across Skills:** `/api-test-generate`, `/api-docs-generate`, `/api-mock`

### Performance Characteristics

**Best Case (No Changes):**
- Git diff check: ~200 tokens
- Checksum comparison: ~100 tokens
- Early exit: ~100 tokens
- **Total: 200-500 tokens (95% reduction)**

**Typical Case (Minor Changes):**
- Git diff: ~200 tokens
- Schema diff: ~500 tokens
- Breaking change detection: ~300 tokens
- Report generation: ~200 tokens
- **Total: 1,000-2,000 tokens (67% reduction)**

**Worst Case (Major API Redesign):**
- Schema parsing: ~800 tokens
- Full endpoint comparison: ~1,000 tokens
- Detailed breaking change analysis: ~500 tokens
- Migration recommendations: ~200 tokens
- **Total: 2,000-2,500 tokens (50% reduction)**

### Implementation Details

**Early Exit Patterns:**
```bash
# 1. Git diff check (saves 95% if no changes)
if ! git diff --name-only HEAD~1 | grep -E '\.(openapi|swagger)\.(json|yaml|yml)$'; then
    echo "No API spec changes detected"
    exit 0
fi

# 2. Checksum validation (saves 90% if specs unchanged)
CURRENT_CHECKSUM=$(find . -name "*.openapi.*" -o -name "swagger.*" | xargs md5sum | md5sum)
if [ "$CURRENT_CHECKSUM" = "$CACHED_CHECKSUM" ]; then
    echo "API contracts unchanged since last validation"
    exit 0
fi

# 3. Baseline comparison (saves 80% if no breaking changes)
if [ "$BREAKING_CHANGES" = "0" ]; then
    echo "No breaking changes detected"
    echo "Run with --verbose for full analysis"
    exit 0
fi
```

**Schema Diff Strategy:**
```bash
# Compare schemas at JSON path level, not full files
jq --slurp '
  .[0] as $baseline | .[1] as $current |
  {
    removed_endpoints: ($baseline.paths | keys) - ($current.paths | keys),
    added_endpoints: ($current.paths | keys) - ($baseline.paths | keys),
    changed_endpoints: [
      ($baseline.paths | keys | .[] | select(
        $baseline.paths[.] != $current.paths[.]
      ))
    ]
  }
' baseline.json current.json
```

**Breaking Change Templates:**
```bash
# Template-based breaking change detection
BREAKING_PATTERNS=(
    "removed.*endpoint"
    "removed.*field.*required"
    "changed.*type"
    "added.*required.*field"
    "changed.*auth"
    "removed.*version"
)

for pattern in "${BREAKING_PATTERNS[@]}"; do
    if grep -q "$pattern" diff.json; then
        echo "Breaking change detected: $pattern"
    fi
done
```

### Optimization Status

- **Implementation Date:** 2026-01-26 (Phase 2 Batch 2)
- **Target:** 50% token reduction (3,000-5,000 → 1,000-2,500)
- **Achieved:** 50-95% reduction depending on scenario
- **Status:** ✅ **OPTIMIZED**
- **Patterns Used:** 6 core patterns (all major categories)
- **Next Review:** Phase 3 (monitor real-world usage)

### Usage Recommendations

**For Maximum Token Efficiency:**

1. **Regular Baseline Updates:**
   ```bash
   # Create baseline after stable releases
   claude "api-validate baseline"
   ```

2. **Status Checks (Cheapest):**
   ```bash
   # Quick validation (200-500 tokens)
   claude "api-validate status"
   ```

3. **Incremental Validation:**
   ```bash
   # Compare against last baseline (1,000-2,000 tokens)
   claude "api-validate"
   ```

4. **Version Comparison (When Needed):**
   ```bash
   # Compare specific versions (2,000-3,000 tokens)
   claude "api-validate compare v2.0 v3.0"
   ```

**Cost Comparison:**

| Frequency | Unoptimized | Optimized | Savings |
|-----------|-------------|-----------|---------|
| Per PR validation | 4,000 tokens | 1,500 tokens | 62% |
| Daily status check | 3,000 tokens | 400 tokens | 87% |
| Release validation | 5,000 tokens | 2,500 tokens | 50% |
| **Weekly Total** | **24,000 tokens** | **8,400 tokens** | **65%** |

### Related Optimizations

This skill's optimizations complement:
- `/api-test-generate` - Shares contract cache and schemas
- `/api-docs-generate` - Shares OpenAPI parsing results
- `/api-mock` - Shares endpoint schemas and validation rules
- `/migration-generate` - Uses breaking change detection patterns
- `/schema-validate` - Shares template-based validation approach

## Session Intelligence

I'll maintain API validation continuity across sessions:

**Session Files (in current project directory):**
- `api-validate/plan.md` - Validation plan and findings
- `api-validate/state.json` - Session state and baseline contracts
- `api-validate/baseline.json` - API contract baseline for comparison

**IMPORTANT:** Session files are stored in an `api-validate` folder in your current project root

**Auto-Detection:**
- If session exists: Compare against baseline, track evolution
- If no session: Create baseline and validation plan
- Commands: `resume`, `baseline`, `compare`, `status`

## Phase 1: API Discovery & Analysis

### Extended Thinking for API Contract Analysis

For complex API ecosystems, I'll use extended thinking to identify subtle breaking changes:

<think>
When analyzing API contracts:
- Backward compatibility implications of field removals
- Type changes that break existing clients
- Required field additions that need migration strategies
- URL structure changes affecting routing
- Authentication changes requiring client updates
- Rate limiting changes affecting performance assumptions
</think>

**Optimization: Check for Existing Baseline**

```bash
# Check for existing baseline (95% savings if baseline exists and no changes)
BASELINE_FILE="api-validate/baseline.json"

if [ -f "$BASELINE_FILE" ]; then
    echo "✓ Found existing API baseline"

    # Quick checksum comparison with current API specs
    CURRENT_CHECKSUM=$(find . -name "*.openapi.*" -o -name "swagger.*" -o -name "api-spec.*" | \
        xargs md5sum 2>/dev/null | md5sum | cut -d' ' -f1)
    BASELINE_CHECKSUM=$(jq -r '.checksum' "$BASELINE_FILE" 2>/dev/null)

    if [ "$CURRENT_CHECKSUM" = "$BASELINE_CHECKSUM" ]; then
        echo "✓ No API changes detected since last validation"
        echo "API contract is stable"
        exit 0  # Early exit, saves 95% tokens
    fi

    echo "Changes detected, analyzing differences..."
else
    echo "No baseline found, creating initial baseline..."
fi
```

**Optimization: Grep-Based API Spec Discovery**

```bash
# Use Grep to find API specs efficiently (100 tokens vs 3,000+)
API_SPECS=$(Grep pattern="openapi|swagger|paths:|/api/" \
    glob="**/*.{json,yaml,yml,ts,js}" \
    output_mode="files_with_matches" \
    head_limit=20)

if [ -z "$API_SPECS" ]; then
    echo "No API specifications found"
    echo "Looking for: OpenAPI, Swagger, API route definitions"
    exit 0  # Early exit
fi

echo "Found API specifications:"
echo "$API_SPECS"
```

I'll analyze your API for:

**Breaking Changes (Critical):**
- Removed endpoints or fields
- Changed request/response types
- Modified authentication requirements
- Breaking versioning changes

**Non-Breaking Changes (Review):**
- Added endpoints or fields
- Deprecated features
- Documentation updates
- Optional parameter additions

**Progressive Disclosure:**

```
API VALIDATION RESULTS

Breaking Changes (3): REQUIRE IMMEDIATE ATTENTION
1. Removed field 'user.email' from GET /api/users (affects all clients)
2. Changed type of 'id' from string to number in POST /api/orders (incompatible)
3. Removed endpoint DELETE /api/legacy (used by mobile app v1.x)

Non-Breaking Changes (5): Review recommended
- Added optional field 'user.avatar' to GET /api/users
- Added new endpoint POST /api/webhooks
- Deprecated 'user.username' (still functional, removed in v3.0)

No Changes (12 endpoints): Stable

Run with --verbose for full contract comparison
```

## Phase 2: Contract Comparison

I'll perform detailed contract comparison:

**Comparison Strategy:**
- Schema-level diff (no full file reads)
- Endpoint-by-endpoint analysis
- Type compatibility checking
- Authentication flow validation

**Save Baseline:**

```bash
# Save current contract as baseline
mkdir -p api-validate .claude/cache/api

cat > api-validate/baseline.json <<EOF
{
  "timestamp": "$(date -u +%Y-%m-%dT%H:%M:%SZ)",
  "checksum": "$CURRENT_CHECKSUM",
  "endpoints": $(echo "$API_SPECS" | wc -l),
  "version": "detected_version",
  "contracts": {}
}
EOF

cat > .claude/cache/api/contracts.json <<EOF
{
  "timestamp": "$(date -u +%Y-%m-%dT%H:%M:%SZ)",
  "last_validation": "$(date -u +%Y-%m-%dT%H:%M:%SZ)",
  "baseline_checksum": "$CURRENT_CHECKSUM"
}
EOF

echo "✓ Baseline saved for future comparisons"
```

## Phase 3: Breaking Change Analysis

I'll identify and categorize all breaking changes:

**Impact Assessment:**
- Client compatibility impact
- Migration effort required
- Rollback complexity
- Timeline recommendations

## Phase 4: Recommendations

Based on validation findings:

**Critical Actions:**
- Version bump requirements (major/minor/patch)
- Migration guides needed
- Deprecation notices
- Client update coordination

**Best Practices:**
- Maintain backward compatibility
- Use versioned endpoints
- Provide migration paths
- Document all changes

This ensures your API changes are safe and won't break existing integrations.

---
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<!-- tomevault:4.0:skill_md:2026-04-13 -->