API Tester — Free Online Tool Test REST APIs: HTTP requests (GET, POST, PUT, DELETE), headers, body, authentication. Online API client like Postman with response viewer.
Use this free online API Tester directly in your browser. No signup required, no data leaves your device. Part of Utilier — a collection of 133+ developer utilities.
What is API Tester (HTTP Client, REST API Testing, Request Builder)? API tester sends HTTP requests to REST APIs with configurable methods (GET POST PUT DELETE PATCH), custom headers for authentication and content type, request body for JSON XML form data, query parameters, and displays responses including status code headers and formatted body with syntax highlighting.
HTTP methods: GET (fetch data), POST (create), PUT/PATCH (update), DELETE (remove). Select method from dropdown.Headers: Authorization (Bearer token, Basic auth), Content-Type (application/json), custom headers. Key-value pairs.Request body: JSON, XML, form data, raw text. JSON editor with syntax highlighting and validation.Response viewer: Status code (200, 404, 500), response headers, formatted body (JSON pretty-print), timing.Collections: Save requests for reuse. Organize by project or endpoint. Import/export collections.Why use api tester? Test APIs without writing code. Debug API issues. Verify endpoints work correctly.
No code needed: Test API immediately. No curl commands or SDKs. Visual interface for building requests.Debug issues: See exact request sent and response received. Check status codes, headers, body.Test authentication: Try different auth methods: Bearer token, API key, Basic auth. See which works.Validate responses: Check response structure matches expected. JSON syntax highlighted for easy reading.When to use api tester Use when testing or debugging REST APIs.
Testing new API endpoints. Debugging API errors (4xx, 5xx status codes). Verifying authentication works. Checking response format and data. Developing frontend (test backend API first). API documentation (test examples). How to use api tester Build request with URL, method, headers, body. Send and view response.
Enter URL: API endpoint: https://api.example.com/users. Add query params: ?page=1&limit=10.Select method: GET (fetch data), POST (create new resource), PUT (update), DELETE (remove).Add headers: Authorization: Bearer YOUR_TOKEN. Content-Type: application/json. Click Add Header for each.Set body: POST/PUT: enter JSON body: {"name": "John", "email": "john@example.com"}. Auto-formats JSON.Send request: Click Send. View response: status 200 OK, headers, body (formatted JSON).Save request: Save to collection for later reuse. Name request: Create User.Key features HTTP methods: GET, POST, PUT, PATCH, DELETE, HEAD, OPTIONS support.Headers editor: Add multiple headers. Autocomplete for common headers. Enable/disable individual headers.Body formats: JSON (with validation), XML, form-data, x-www-form-urlencoded, raw text, binary.Auth helpers: Bearer token, Basic auth (username/password), API key, OAuth 2.0 presets.Response viewer: Status code with description, headers table, formatted body (JSON/XML), raw view, timing stats.Collections: Save, organize, share request collections. Import/export JSON format.Common use cases Test GET endpoint: GET https://api.github.com/users/octocat. Headers: none. Response: user data JSON, status 200.Create resource: POST https://api.example.com/users. Body: {"name": "Alice"}. Header: Content-Type: application/json. Response: created user, status 201.Test auth: Add header: Authorization: Bearer abc123. GET /protected. Check status: 200 (authorized) or 401 (unauthorized).Examples Common API request examples.
GET request GET https://api.example.com/users?page=1Status: 200 OK
Body: [{"id": 1, "name": "Alice"}]Fetch users with pagination.
POST JSON POST https://api.example.com/users
Body: {"name": "Bob"}Status: 201 Created
Body: {"id": 2, "name": "Bob"}Create new user.
Technical reference HTTP request components and formats.
Methods GET (retrieve), POST (create), PUT (replace), PATCH (update), DELETE (remove), HEAD (headers only), OPTIONS (allowed methods). Headers Authorization, Content-Type, Accept, User-Agent, custom headers. Format: key: value. Body types JSON (application/json), XML (application/xml), form-data (multipart/form-data), urlencoded (application/x-www-form-urlencoded). Status codes 2xx (success: 200 OK, 201 Created), 4xx (client error: 400 Bad Request, 401 Unauthorized, 404 Not Found), 5xx (server error: 500 Internal Server Error). Common mistakes to avoid Wrong Content-Type header (server rejects request) Why it happens: JSON body with Content-Type: text/plain → server doesn't parse as JSON.
How to avoid it: Match Content-Type to body: application/json for JSON, application/xml for XML. Set header explicitly.
Frequently asked questions What is the difference between PUT and PATCH? PUT: replace entire resource (send all fields). PATCH: update partial resource (send only changed fields). Example: PUT updates whole user object, PATCH updates just email field.
How do I add authentication? Bearer token: Header Authorization: Bearer YOUR_TOKEN. Basic auth: Authorization: Basic base64(username:password). API key: custom header or query param.
Privacy and availability Runs entirely in your browser — zero server processing No signup or account required Works offline once loaded Fast, lightweight, no external dependencies Available as a browser extension for Chrome and Firefox Tags HTTP Networking API Related tools cURL Converter — Convert a curl command to fetch, Axios, React, Python, Go, PHP, Java or Rust — and fetch back to curl.JSON Beautifier & Validator — Format, minify and validate JSON. 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