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API Testing Tools

Practical tools for testing, debugging, and validating APIs during development and integration work.

cURL

Command-line HTTP client. Cross-platform, scriptable, supports all methods and auth types.

# GET request
curl -X GET https://api.example.com/users

# POST with JSON
curl -X POST \
  -H "Content-Type: application/json" \
  -d '{"name":"John"}' \
  https://api.example.com/users

# With auth header
curl -H "Authorization: Bearer TOKEN" https://api.example.com/data

# Upload file
curl -X POST -F "file=@photo.jpg" https://api.example.com/upload

# Verbose output (debug TLS, headers)
curl -v https://api.example.com/users

Key flags: -X (method), -H (headers), -d (data/body), -u (credentials), -k (skip SSL), -v (verbose), -o (output to file).

Chrome DevTools (Network Tab)

Open with F12. Monitor all network requests in real-time.

Key panels: Headers (request/response, status), Preview (formatted), Response (raw), Timing (DNS, TCP, TLS, TTFB, Download), Cookies.

Workflow: Open DevTools -> Network tab -> perform action -> click request -> inspect. Use "Copy as cURL" to reproduce requests in terminal.

Timing waterfall: DNS lookup -> TCP connect -> TLS handshake -> Time to First Byte -> Content Download.

Filters: XHR, JS, CSS, Img, Media, Font, Doc, WS. Throttle network speed for slow connection testing.

Postman

GUI-based API testing platform.

Key features: - Collections and folders for request organization - Environment variables (dev/staging/prod) - Request chaining with variable extraction - Pre-request and test scripts (JavaScript) - Mock servers for API prototyping - Newman CLI for CI/CD integration - Import/export OpenAPI specs

Testing workflow: 

pm.test("Status is 200", () => {
  pm.response.to.have.status(200);
});

pm.test("Response has user ID", () => {
  const json = pm.response.json();
  pm.expect(json.id).to.be.a("number");
});

Swagger UI / Editor

Interactive documentation and testing for OpenAPI specs. Write/edit YAML/JSON with live preview. Test endpoints directly from docs.

Tool Comparison

Feature cURL DevTools Postman
Environment CLI Browser GUI/CLI
Automation Shell scripts Limited Collections/Newman
Collaboration None None Teams/Workspaces
Best for Quick tests, CI/CD Live traffic debugging Complex API testing

SoapUI (SOAP Testing)

  1. Create SOAP project with WSDL URL
  2. Create TestSuite and TestCases
  3. Add SOAP Request steps with assertions
  4. Run - assertions show pass/fail

Gotchas

  • cURL -k in production - skip SSL verification only in dev, never in prod
  • Postman environment leaks - don't commit Postman environments with secrets to git
  • DevTools caching - disable cache checkbox to test without browser cache
  • Copy as cURL from DevTools includes cookies - sanitize before sharing

See Also