Endpoint Validator Skill

Deterministic HTTP endpoint validation following a Discover, Validate, Report pattern. Finds endpoints, tests each against expectations, and produces machine-readable results with clear pass/fail verdicts and CI-compatible exit codes.

Reference Loading Table

Signal	Load These Files	Why
Security header WARNs, HSTS/CSP/X-Frame issues	security-headers.md	Routes to the matching deep reference
Config errors, hardcoded IPs, timeout problems	endpoint-config-preferred-patterns.md	Routes to the matching deep reference
401/403 failures, Bearer/API-key/cookie auth	auth-endpoint-patterns.md	Routes to the matching deep reference

Instructions

Phase 1: DISCOVER

Goal: Locate or receive endpoint definitions before making any requests.

Step 1: Read repository CLAUDE.md

Check for and follow any repository-level CLAUDE.md before running validation. It may contain base URL conventions, environment variable names, or endpoint paths relevant to the project.

Step 2: Search for endpoint configuration

Look for definitions in priority order:

1. endpoints.json in project root
2. tests/endpoints.json
3. Inline specification provided by user or calling agent

Prefer config files checked into version control over ad-hoc endpoint lists. Manually listing endpoints every run leads to drift and missed endpoints.

Step 3: Parse and validate configuration

Configuration must contain base_url and at least one endpoint:

{
  "base_url": "http://localhost:8000",
  "endpoints": [
    {"path": "/health", "expect_status": 200},
    {"path": "/api/v1/users", "expect_key": "data", "timeout": 10},
    {"path": "/api/v1/search?q=test", "max_time": 2.0}
  ]
}

Each endpoint supports these fields:

• path (required): URL path appended to base_url
• expect_status (default: 200): Expected HTTP status code
• expect_key (optional): Top-level JSON key that must exist in response. Only top-level key presence is checked -- full JSON schema validation is out of scope.
• timeout (default: 5): Request timeout in seconds. The 5-second default prevents hanging on unresponsive endpoints.
• max_time (optional): Fail if response exceeds this threshold in seconds
• method (optional): HTTP method. Defaults to GET. POST/PUT/DELETE require explicit configuration with a request body -- send mutating requests only when the user explicitly configures them.
• headers (optional): Additional headers per endpoint (e.g., Accept, Content-Type, Authorization)

If base_url points to a production host and the config includes POST/PUT/DELETE endpoints, warn the user before proceeding. Mutating production data or triggering rate limits during a smoke test is a serious risk. Use staging environments for write operations; reserve production for GET-only health checks.

Use hostnames or environment variables instead of hardcoded IP addresses in base_url (e.g., http://192.168.1.42:8000). They break on every other machine and CI environment. Use localhost with a configurable port or environment variables instead.

Step 4: Confirm base URL is reachable

Make a single request to base_url before running the full suite. If unreachable, report immediately rather than failing every endpoint individually.

Gate: Configuration parsed, base URL reachable, at least one endpoint defined. Proceed only when gate passes.

Phase 2: VALIDATE

Opus 4.7 override: Opus 4.7 trades tool calls for reasoning by default. In verification, that default is wrong. Run the command. Do not reason about whether the command would pass. Do not summarize the expected output. Execute the check, paste the exit code, paste the relevant output. A verification phase that produces a verdict without an observed tool result is not a verification — it is a guess with a rigor aesthetic.

Goal: Test each endpoint against its expected criteria and collect structured results.

Step 1: Execute requests sequentially

Test endpoints one at a time for predictable, reproducible output. For each endpoint:

1. Construct full URL from base_url + path
2. Send request with configured method (GET by default) and timeout
3. Record status code, response time, and body
4. Display each result as it completes so the user sees progress

This skill sends one request per endpoint. It is not a load tester or stress tester -- it validates contract compliance, not throughput.

Step 2: Evaluate against expectations

For each response, check in order:

1. Status code: Does it match expect_status? If not, mark FAIL.
2. JSON key: If expect_key set, parse JSON and check key exists. If missing or not valid JSON, mark FAIL.
3. Response time: If max_time set and elapsed exceeds it, mark SLOW. Flag slow endpoints -- they indicate degradation that becomes failure under load.
4. Security headers: Check response headers for common security headers. Report missing headers as WARN (not FAIL):
   • Strict-Transport-Security -- HSTS enforcement (expected on HTTPS endpoints)
   • Content-Security-Policy -- XSS mitigation
   • X-Content-Type-Options -- should be nosniff
   • X-Frame-Options -- clickjacking prevention (or CSP frame-ancestors)

Skip security header checks for localhost/127.0.0.1 endpoints (development environments typically omit these). Only check on non-localhost base URLs unless explicitly configured.

Step 3: Handle failures gracefully

• Connection refused: Record as FAIL with "Connection refused" error
• Timeout exceeded: Record as FAIL with "Timeout after Ns" error
• Invalid JSON when expect_key set: Record as FAIL with "Invalid JSON response"
• Unexpected exception: Record as FAIL with exception message

Gate: All endpoints tested. Every result has a clear PASS, FAIL, or SLOW verdict. Proceed only when gate passes.

Phase 3: REPORT

Goal: Produce structured, machine-readable output with summary statistics.

Step 1: Format individual results

ENDPOINT VALIDATION REPORT
==========================
Base URL: http://localhost:8000
Endpoints: 15 tested

RESULTS:
  /api/health                    200 OK      45ms
  /api/users                     200 OK     123ms
  /api/products                  500 FAIL   "Internal Server Error"
  /api/slow                      200 SLOW   3.2s > 2.0s threshold

SECURITY HEADERS (non-localhost only):
  /api/health                    WARN  Missing: Content-Security-Policy, X-Frame-Options
  /api/users                     OK    All security headers present
  /api/products                  SKIP  (endpoint failed)

Step 2: Produce summary

SUMMARY:
  Passed: 13/15 (86.7%)
  Failed: 1 (status error)
  Slow: 1 (exceeded threshold)
  Security header warnings: 3 endpoints missing headers

Step 3: Set exit code

• Exit 0 if all endpoints passed (SLOW counts as pass unless max_time was set)
• Exit 1 if any endpoint failed

Gate: Report printed, exit code set. Validation complete.

Examples

Example 1: Pre-Deployment Health Check

User says: "Validate all endpoints before we deploy" Actions:

1. Find endpoints.json in project root (DISCOVER)
2. Test each endpoint, collect status codes and times (VALIDATE)
3. Print report, exit 0 if all pass (REPORT) Result: Structured pass/fail report with CI-compatible exit code

Example 2: Smoke Test After Migration

User says: "Check if the API is still working after the database migration" Actions:

1. Read endpoint config, confirm base URL reachable (DISCOVER)
2. Hit each endpoint, check status and expected keys (VALIDATE)
3. Surface any failures with error details (REPORT) Result: Quick verification that migration did not break API contracts

---

Error Handling

Error: "Base URL Unreachable"

Cause: Service not running, wrong port, or network issue Solution:

1. Verify service is running (ps aux, docker ps, or equivalent)
2. Confirm port matches config (netstat -tlnp or ss -tlnp)
3. Check for firewall rules or container networking issues

Error: "All Endpoints Timeout"

Cause: Service overwhelmed, wrong host, or proxy misconfiguration Solution:

1. Test a single endpoint manually with curl -v
2. Increase timeout values in config if service is legitimately slow
3. Check if a reverse proxy or load balancer is intercepting requests

Error: "JSON Parse Failure on expect_key Check"

Cause: Endpoint returns HTML, XML, or empty body instead of JSON Solution:

1. Verify endpoint actually returns JSON (check Content-Type header)
2. Remove expect_key if endpoint legitimately returns non-JSON
3. Check if authentication is required (HTML login page returned)

---

Reference Loading

Task Type	Load This Reference
Security header WARNs, HSTS/CSP/X-Frame issues	references/security-headers.md
Config errors, hardcoded IPs, timeout problems	references/endpoint-config-preferred-patterns.md
401/403 failures, Bearer/API-key/cookie auth	references/auth-endpoint-patterns.md

---

References

CI/CD Integration

# GitHub Actions example
# TODO: scripts/validate_endpoints.py not yet implemented
# Manual alternative: use curl to validate endpoints from endpoints.json
- name: Validate API endpoints
  run: |
    jq -r '.endpoints[].path' endpoints.json | while read path; do
      curl -sf "$BASE_URL$path" > /dev/null && echo "PASS: $path" || echo "FAIL: $path"
    done

# Pre-deployment gate
# TODO: scripts/validate_endpoints.py not yet implemented
# Manual alternative: iterate endpoints.json with curl
jq -r '.endpoints[].path' endpoints.json | while read path; do
  curl -sf "http://localhost:8000$path" > /dev/null || { echo "FAIL: $path"; exit 1; }
done