API Testing

When to Use

• Testing REST API endpoints for correct responses
• Writing declarative, repeatable HTTP test suites
• Chaining HTTP requests (authenticate → create → verify)
• Probing multiple URLs for availability, status codes, or headers
• Validating response bodies, headers, and status codes with assertions

Tools

Patterns

Hurl: Simple GET with status assertion

Create a .hurl file:

GET http://localhost:3000/api/health
HTTP 200
[Asserts]
jsonpath "$.status" == "ok"

Run it:

hurl health.hurl

Hurl: POST with JSON body and response validation

POST http://localhost:3000/api/users
Content-Type: application/json
{
  "name": "Alice",
  "email": "alice@example.com"
}
HTTP 201
[Asserts]
jsonpath "$.id" isInteger
jsonpath "$.name" == "Alice"

Hurl: Chained requests (auth → create → verify)

# Step 1: Login
POST http://localhost:3000/api/auth/login
Content-Type: application/json
{
  "email": "admin@example.com",
  "password": "secret"
}
HTTP 200
[Captures]
token: jsonpath "$.token"

# Step 2: Create resource with token
POST http://localhost:3000/api/items
Authorization: Bearer {{token}}
Content-Type: application/json
{
  "title": "New Item"
}
HTTP 201
[Captures]
item_id: jsonpath "$.id"

# Step 3: Verify resource exists
GET http://localhost:3000/api/items/{{item_id}}
Authorization: Bearer {{token}}
HTTP 200
[Asserts]
jsonpath "$.title" == "New Item"

Hurl: Run test suite with JSON report

hurl --test --report-json report/ tests/*.hurl

Hurl: Use variables from command line

hurl --variable host=https://staging.example.com --variable token=abc123 tests/api.hurl

httpx: Probe a list of URLs for status codes

echo -e "https://example.com\nhttps://httpbin.org\nhttps://nonexistent.invalid" | httpx -silent -status-code

httpx: Probe with full JSON output (status, title, tech)

echo "https://example.com" | httpx -json -title -tech-detect -status-code

httpx: Check specific ports across hosts

echo -e "192.168.1.1\n192.168.1.2" | httpx -ports 80,443,8080 -status-code

httpx: Follow redirects and show final URL

echo "http://github.com" | httpx -follow-redirects -location -status-code

Pipelines

Hurl test suite → summarize failures

hurl --test --report-json report/ tests/*.hurl 2>&1; jq '[.[] | select(.success == false) | {file: .filename, errors: [.entries[] | select(.errors | length > 0) | .errors]}]' report/*.json

Each stage: Hurl runs all tests and writes JSON reports, jq filters to failures and extracts error details.

Discover endpoints with Katana → probe with httpx

katana -u https://example.com -silent -d 2 | httpx -silent -status-code -json

Each stage: Katana crawls and discovers URLs, httpx probes each for status and metadata.

Prefer Over

• Prefer Hurl over curl scripts for multi-step API testing — declarative syntax with built-in assertions, no bash scripting needed
• Prefer Hurl over Postman/Bruno for CI-friendly test suites — plain text files, no GUI dependency
• Prefer httpx over curl loops for probing many URLs — concurrent, structured output, built for scale

Do NOT Use When

• Need full browser rendering or JavaScript execution — use web-crawling skill (Playwright)
• Building a long-running API client or SDK — write code instead
• Testing WebSocket or gRPC endpoints — use specialized tools (wscat, grpcurl)
• Single ad-hoc curl request — just use curl directly