REST API Client Online — Free Postman Alternative

A free, browser-based REST client for sending HTTP requests with custom headers, authentication, and JSON or form bodies. Inspect formatted responses, save your last 10 requests locally, and export anything as cURL — no install, no signup. Note: subject to browser CORS rules; works best with public APIs and APIs you control.

Headers

infoClick Send to issue a request — the response appears here.

cloud

No response yet.

Recent requests (0/10)

Nothing yet — your last 10 requests will appear here and are stored only in your browser localStorage.

What is a REST API Client?

A REST API client is a tool that builds, sends, and inspects HTTP requests against a REST endpoint. It lets developers exercise an API without writing throwaway curl commands or test scripts — pick a method, set headers and body, hit Send, and read the response. Modern clients (Postman, Insomnia, Bruno) ship as desktop apps; OpenFormatter's REST client lives in your browser tab so there is nothing to install.

Under the hood every request becomes a single browser fetch() call wired to an AbortController for cancellation. Headers, query params, and the body are constructed from the form fields, the response is read as text, and JSON content is auto pretty-printed in the response panel. The full request can be copied as a runnable cURL command for use in scripts or tickets.

How to test an API in 4 steps

Enter the URL and method. Pick GET / POST / PUT / PATCH / DELETE / HEAD / OPTIONS, then paste the endpoint into the address bar above. Use the Sample dropdown for one-click public APIs.
Configure headers, auth, body, and params. Use the four request tabs to add custom headers, choose Bearer / Basic / API Key authentication, attach a JSON or form body, and append query parameters. The final URL preview updates live.
Click Send. The browser issues the request via fetch(). A spinner shows the in-flight state; click Cancel to abort the request through the AbortController.
Inspect the response. A color-coded status badge, response time, and size appear at the top. Switch between Body (auto-formatted JSON), Headers (key/value table), and Raw (original text). Copy the body, download it, or export the entire request as cURL.

Sample request and response

A simple GET against the GitHub user API returns a JSON object the client formats automatically.

Request

GET https://api.github.com/users/octocat
Accept: application/vnd.github+json
User-Agent: openformatter-rest-client

Response (200 OK)

{
  "login": "octocat",
  "id": 583231,
  "node_id": "MDQ6VXNlcjU4MzIzMQ==",
  "type": "User",
  "name": "The Octocat",
  "company": "@github",
  "blog": "https://github.blog",
  "public_repos": 8,
  "followers": 14242
}

All HTTP Methods

GET, POST, PUT, PATCH, DELETE, HEAD, and OPTIONS — with automatic Content-Type negotiation for JSON, form, and plain-text bodies.

Auth + Custom Headers

Bearer tokens, HTTP Basic, and API keys (header or query). Mix in any custom headers from a quick-pick list of common ones — Accept, Cookie, X-API-Key, and more.

Auto JSON Formatting

JSON responses are detected from Content-Type and pretty-printed with two-space indentation. View Raw for the original payload, or download to disk.

Common use cases

check_circleDebugging a third-party REST API to confirm response shape and status codes
check_circleSmoke-testing your own backend endpoints during development without leaving the browser
check_circleTriggering webhooks (Stripe, GitHub, Slack) to verify the receiving handler
check_circleLearning REST and HTTP basics by exercising public sandbox APIs
check_circlePrototyping a request before pasting the cURL into a script or CI pipeline
check_circleSending GraphQL queries via POST with a JSON body containing query and variables
check_circleTesting OAuth-protected APIs by pasting in a Bearer access token
check_circleConfirming custom headers, CORS preflights, and content negotiation against staging endpoints

When to use this vs Postman vs curl

Reach for the OpenFormatter REST client when you want a single browser tab, no install, and a quick check of a public or CORS-enabled API. Use a desktop client like Postman or Insomnia when you need cloud-synced collections, team workspaces, scripting (pre-request hooks), file uploads, or to bypass CORS entirely. Reach for curl when the request belongs in a shell script, a CI step, a Dockerfile health check, or a one-line reproduction in a bug report.

Feature	OpenFormatter REST	Postman	curl	Insomnia
Install required	No (browser)	Yes	Yes (CLI)	Yes
Pricing	Free	Free + paid	Free	Free + paid
CORS-restricted APIs	Need CORS headers	Yes (proxies)	Yes (no CORS)	CORS proxy add-on
Save requests	localStorage (10)	Cloud sync	Files	Cloud sync
Team collaboration	No	Yes	No	Yes
Best for	Quick API tests	Team API workflows	Scripts	Solo devs

warningHeads-up about CORS

Browsers block JavaScript from reading the body of a cross-origin response unless the server returns Access-Control-Allow-Origin. Because this client runs in your browser, it cannot bypass that rule. APIs that work out of the box include: jsonplaceholder.typicode.com, httpbin.org, api.github.com, dog.ceo, api.coindesk.com, and most public REST sandboxes. APIs that block browser requests (most internal corporate APIs, many banking and SaaS APIs) require Postman, Insomnia, or a server-side proxy.

Working with JSON?

Format, validate, and convert API responses with the rest of OpenFormatter's JSON toolkit — all browser-side.

JSON Formatter JSON Validator JSON to TypeScript

Frequently Asked Questions

What is CORS and why does my API request fail?

CORS (Cross-Origin Resource Sharing) is a browser security policy that blocks JavaScript from reading responses from a different origin unless the server opts in with Access-Control-Allow-Origin headers. Because this REST client runs in your browser, it cannot bypass that policy. If a request fails with a network error and no status code, the API likely does not allow browser requests from openformatter.com. Use a CORS-friendly endpoint (httpbin.org, jsonplaceholder.typicode.com, dog.ceo) or call the API from your own server-side proxy.

How is this different from Postman or Insomnia?

Postman and Insomnia are native desktop apps, so they can ignore CORS, upload files, and store unlimited request collections in the cloud. This REST client is a single web page — there is nothing to install, nothing to sign up for, and nothing leaves your browser. It is ideal for quick API checks, sharing a one-off request, or testing endpoints from a locked-down workstation. For team workflows or CORS-restricted internal APIs, use a desktop client.

Can I save requests across browser sessions?

Yes — your last 10 requests are stored under the localStorage key of-rest-client-history and survive page reloads and browser restarts. Click any entry in the history list to reload that method and URL into the form. Storage is per-browser and never synced anywhere; clearing site data or using private browsing wipes it.

Why doesn’t file upload work?

You can build a multipart/form-data request, but the browser will not attach a real file picker through this tool. Modern browsers refuse multipart uploads to most third-party origins because of CORS preflight rules around Content-Type. Use a POST with a JSON body for endpoints that accept base64-encoded files, or run a desktop client when you need true file uploads.

How do I send Bearer token authentication?

Open the Auth tab, choose Bearer Token, and paste your token. The client adds an Authorization: Bearer <token> header to every request automatically — you do not need to add it under Headers. The same field works for OAuth 2.0 access tokens, JWTs, and personal access tokens (GitHub, GitLab, Linear).

Can I send GraphQL queries?

Yes. Set the method to POST, point the URL at your GraphQL endpoint (for example https://api.github.com/graphql), set body type to JSON, and send a body of the shape {"query": "{ viewer { login } }", "variables": {}}. Add Authorization: Bearer <token> via the Auth tab. The response is returned as JSON and pretty-printed in the response panel.

Are my API tokens stored on your server?

No — never. There is no server. Headers, tokens, and request bodies live only in your browser tab’s memory. Only the request method and URL of recent requests are written to localStorage (under of-rest-client-history); auth headers, body payloads, and responses are never persisted. You can verify this in DevTools → Application → Local Storage.

What is the request timeout?

There is no explicit timeout — the request runs until the browser default network timeout (typically 30–300 seconds depending on the browser and platform). Each request is wired to an AbortController, so you can click Cancel at any time and the in-flight fetch is aborted cleanly. If you need a hard timeout, send and click Cancel after your chosen interval.