librefang-registry/hands/apitester/SKILL.md

name, version, description, runtime

name	version	description	runtime
apitester-hand-skill	1.0.0	Expert knowledge for AI API testing -- HTTP reference, testing patterns, OpenAPI parsing, and load testing techniques	prompt_only

API Testing Expert Knowledge

HTTP Reference

Status Code Categories

Range	Category	Common Codes
2xx	Success	200 OK, 201 Created, 204 No Content
3xx	Redirection	301 Moved, 304 Not Modified
4xx	Client Error	400 Bad Request, 401 Unauthorized, 403 Forbidden, 404 Not Found, 422 Unprocessable, 429 Too Many Requests
5xx	Server Error	500 Internal, 502 Bad Gateway, 503 Service Unavailable, 504 Gateway Timeout

curl Quick Reference

GET with headers:

curl -s -H "Authorization: Bearer TOKEN" \
  -H "Accept: application/json" \
  "https://api.example.com/endpoint"

POST with JSON body:

curl -s -X POST \
  -H "Authorization: Bearer TOKEN" \
  -H "Content-Type: application/json" \
  -d '{"key": "value"}' \
  "https://api.example.com/endpoint"

Timing information:

curl -s -o /dev/null -w "status:%{http_code} time:%{time_total}s size:%{size_download}b" \
  "https://api.example.com/endpoint"

Verbose with headers:

curl -v -H "Authorization: Bearer TOKEN" \
  "https://api.example.com/endpoint" 2>&1

---

Testing Patterns

Functional Testing Checklist

For each endpoint, test:

1. Happy path: Valid request with all required parameters
2. Missing required fields: Omit each required field one at a time
3. Invalid data types: String where number expected, etc.
4. Boundary values: Min/max for numbers, empty strings, very long strings
5. Special characters: Unicode, HTML entities, SQL keywords
6. Null values: Explicit null vs missing field
7. Authentication: Valid, invalid, missing, expired tokens
8. Authorization: Access own resources, access others' resources
9. Pagination: First page, last page, beyond last page, invalid page
10. Filtering/Sorting: Valid filters, invalid filters, combined filters

Test Data Patterns

# Safe test strings for injection testing
SQL injection:    "'; DROP TABLE users; --"
XSS:             "<script>alert('xss')</script>"
Command injection: "; cat /etc/passwd"
Path traversal:   "../../etc/passwd"
Long string:      "A" * 10000
Unicode:          "\u0000\u0001\u0002"
Email format:     "test@example.com" (use example.com domain)

Response Validation

Check every response for:

1. Status code is expected
2. Content-Type header is correct
3. Response body parses as valid JSON/XML
4. Required fields are present
5. Field types match schema
6. No unexpected fields (strict mode)
7. No sensitive data exposure (passwords, tokens, PII)
8. Pagination metadata is correct
9. Error responses follow a consistent format
10. Response time is within acceptable range

---

OpenAPI/Swagger Parsing

Key OpenAPI 3.0 Structure

{
  "openapi": "3.0.0",
  "info": {"title": "API Name", "version": "1.0"},
  "paths": {
    "/users": {
      "get": {
        "parameters": [...],
        "responses": {
          "200": {"description": "Success", "content": {"application/json": {"schema": {...}}}}
        }
      },
      "post": {
        "requestBody": {"content": {"application/json": {"schema": {...}}}},
        "responses": {...}
      }
    }
  },
  "components": {
    "schemas": {...},
    "securitySchemes": {...}
  }
}

Extracting Test Cases from OpenAPI

For each path + method combination:

1. Extract required parameters (path, query, header)
2. Extract request body schema (for POST/PUT/PATCH)
3. Extract expected response schemas per status code
4. Note security requirements
5. Generate positive and negative test cases

---

Load Testing Techniques

Ramp-Up Pattern

Phase 1: 10 concurrent users for 30 seconds (warm up)
Phase 2: 50 concurrent users for 60 seconds (moderate load)
Phase 3: 100 concurrent users for 60 seconds (high load)
Phase 4: 200 concurrent users for 30 seconds (stress test)
Phase 5: 10 concurrent users for 30 seconds (recovery check)

Key Metrics to Track

Metric	Formula	Acceptable	Warning	Critical
Avg Response Time	sum(times)/count	<200ms	200-500ms	>500ms
P95 Response Time	95th percentile	<500ms	500ms-1s	>1s
Error Rate	errors/total*100	<1%	1-5%	>5%
Throughput	requests/second	Depends	Decreasing	Dropping

Shell-Based Load Testing

Simple concurrent requests:

# Send 50 concurrent requests
for i in $(seq 1 50); do
  curl -s -o /dev/null -w "%{http_code} %{time_total}\n" \
    -H "Authorization: Bearer TOKEN" \
    "https://api.example.com/endpoint" &
done
wait

Sustained load test with timing:

# 100 requests, 10 at a time
for batch in $(seq 1 10); do
  for i in $(seq 1 10); do
    curl -s -o /dev/null -w "%{http_code} %{time_total}\n" \
      "https://api.example.com/endpoint" &
  done
  wait
  sleep 1
done

---

Security Testing Reference

OWASP API Security Top 10

1. Broken Object Level Authorization: Access other users' data by changing IDs
2. Broken Authentication: Weak auth mechanisms, missing rate limits
3. Broken Object Property Level Authorization: Mass assignment, excessive data exposure
4. Unrestricted Resource Consumption: Missing rate limits, large payloads
5. Broken Function Level Authorization: Access admin endpoints as regular user
6. Unrestricted Access to Sensitive Business Flows: Abuse of purchase, reservation, etc.
7. Server-Side Request Forgery: API fetches attacker-controlled URLs
8. Security Misconfiguration: Default configs, verbose errors, missing headers
9. Improper Inventory Management: Exposed old API versions, debug endpoints
10. Unsafe Consumption of APIs: Trusting third-party API responses without validation

Security Headers to Check

Strict-Transport-Security: max-age=31536000
X-Content-Type-Options: nosniff
X-Frame-Options: DENY
Content-Security-Policy: default-src 'self'
X-XSS-Protection: 1; mode=block
Cache-Control: no-store (for sensitive endpoints)

---

Test Report Templates

Per-Endpoint Result Format

{
  "endpoint": "/api/users",
  "method": "GET",
  "tests": [
    {"name": "Happy path", "status": "PASS", "code": 200, "time_ms": 45},
    {"name": "Missing auth", "status": "PASS", "code": 401, "time_ms": 12},
    {"name": "Invalid ID", "status": "FAIL", "code": 500, "time_ms": 230, "note": "Expected 404, got 500"}
  ]
}

Regression Detection

Compare two test runs:

Field Changed:  response.data[].email field removed
Impact:         Breaking change for API consumers
Severity:       HIGH
First Seen:     2025-01-15 run
Previous Value: string (email format)
Current Value:  field absent