Tester Rest Api
Fast, accurate and free online tester rest api tool running directly in your browser.
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Other tools you may find usefulREST API tester - test HTTP endpoints in the browser
REST API tester allows you to send HTTP requests (GET, POST, PUT, PATCH, DELETE) to any endpoint and see the response: status code, headers, body JSON/XML. An alternative to Postman and curl – without installation, directly in the browser.
HTTP methods and their applications
GET: get data (without side effects). POST: create a new resource or send data. PUT: replace entire resource. PATCH: partial update. DELETE: delete a resource. HEAD: only headers (no body). OPTIONS: check supported methods (CORS preflight). CONNECT/TRACE: Rarely used in REST. Idempotency: GET, PUT, DELETE = same result multiple times.
HTTP Headers in the API
Content-Type: application/json (body is JSON). Accept: application/json (I expect JSON). Authorization: Bearer TOKEN (JWT/OAuth). X-API-Key: API key. X-Request-ID: UUID of the request for tracing. Cache-Control: no-cache. User-Agent: customer identification. CORS headers: Access-Control-Allow-Origin (server → client).
HTTP response codes
2xx success: 200 OK, 201 Created, 204 No Content. 3xx redirects: 301 Moved Permanently, 302 Found, 304 Not Modified. 4xx client errors: 400 Bad Request, 401 Unauthorized, 403 Forbidden, 404 Not Found, 422 Unprocessable Entity, 429 Too Many Requests. 5xx server errors: 500 Internal Server Error, 502 Bad Gateway, 503 Service Unavailable.
REST API vs GraphQL vs gRPC
REST: Simple, Resource-Based and HTTP. Language independent. GraphQL: one endpoint, the client determines the shape of the response. Flexible, good for complex UIs. gRPC: Protocol Buffers, fast, binary, ideal for microservices. WebSocket: bidirectional, real-time. Most public APIs: REST. Internal microservices: gRPC.
FAQ
How to test API with Bearer authorization?
Add header: Authorization: Bearer eyJhbGciOiJIUzI1NiJ9... Token download: POST /auth/login from {username, password} → response.token. Refresh: POST /auth/refresh with refresh_token. Expiry: check exp claim in JWT (JWT decoder tool on this page). Basic Auth: Authorization: Basic base64(user:pass).
How to debug CORS errors in API?
Error: "Access to fetch at X from origin Y has been blocked by CORS policy." Check if the server returns Access-Control-Allow-Origin: * or Access-Control-Allow-Origin: your-domain. Preflight (OPTIONS): Content-Type: application/json requires preflight. Server solution: add CORS headers. Temporarily: CORS proxy or localhost proxy (Vite, CRA have proxy config).
How to send JSON in POST request?
Content-Type: application/json (MANDATORY). Body: {"key": "value", "number": 42}. Curl: curl -X POST URL -H "Content-Type: application/json" -d '{"key":"val"}'. Fetch JS: fetch(URL, {method:"POST", headers:{"Content-Type":"application/json"}, body: JSON.stringify(data)}). Axios: axios.post(URL, data) – automatically adds Content-Type.
How to test API locally?
localhost vs 127.0.0.1: same (aliases). HTTPS local: mkcert (local CA), Vite --https, ngrok (public tunnel). Mock API: json-server (npm), WireMock, msw (Mock Service Worker). Postman: collections, environments, automated tests. Insomnia: an open-source alternative. Bruno: offline-first, collection files in git.
How does rate limiting affect API tests?
429 Too Many Requests: you have exceeded the limit. Headers: X-RateLimit-Limit (max), X-RateLimit-Remaining (remained), X-RateLimit-Reset (when reset, Unix timestamp). Retry-After: how many seconds to wait. Exponential backoff: 1s, 2s, 4s, 8s... Rate limit testing: check API documentation before mass requests.
Related tools: JWT parser, JSON formatting and HTTP header generator.