Free Online API Tester: A Postman Alternative in Your Browser

Send GET, POST and PUT requests, inspect responses, and export cURL, fetch or Python code with our free browser-based API tester — no install, no login.

Every developer, marketer and AI builder eventually needs to poke at an API: check a webhook payload, confirm a CRM endpoint returns what the docs promise, or debug why a fetch call fails in the browser. Desktop clients work, but they mean installs, accounts and sync prompts. Our free API Tester gives you a Postman-style HTTP client that runs in your browser — no download, no login required.

What the API Tester Does

It is a full request builder and response inspector in one page:

Any method — GET, POST, PUT, PATCH, DELETE, HEAD and OPTIONS.
Query params — add, toggle and remove key/value pairs; they are merged into the URL for you.
Custom headers — set Accept, Content-Type, tracing headers or anything else the API expects.
Request bodies — JSON (with formatting), raw text, or form-encoded fields.
Auth helpers — Bearer token, Basic auth, or a custom API-key header, built for you instead of hand-typed.
Response viewer — status code, response time, payload size, pretty-printed JSON, raw body and the full response header list.
Code export — copy the same request as cURL, JavaScript fetch, or Python requests.
History and collections — recent requests are kept in your browser; sign in to save named requests into collections you can reuse later.

Why Browser-Only API Testing Usually Breaks

If you have ever tried calling a third-party API from the browser console, you have met CORS. Most APIs do not send Access-Control-Allow-Origin headers for arbitrary web pages, so the browser blocks the response before your code ever sees it — even though the server answered correctly.

The API Tester solves this by relaying every request through our own server-side proxy. Your request leaves our infrastructure, not your browser, so CORS never applies. You get the real status code, the real headers and the real body.

Built With Safety Guardrails

An open request relay is a classic SSRF (server-side request forgery) target, so the proxy is deliberately narrow:

Only public https:// endpoints are allowed.
localhost, loopback and private network ranges are blocked.
Cloud metadata addresses (such as 169.254.169.254) are rejected outright.
Requests time out after 15 seconds, and responses are capped at 1 MB.
Redirects are not followed blindly to a blocked destination.

These limits mean the tool is safe to leave public — and they are the same limits you should apply if you build a request relay of your own.

A Typical Workflow

Pick a method and paste the endpoint URL.
Add query params under Params and any required headers under Headers.
If the API needs credentials, open Auth and choose Bearer, Basic or API key.
For writes, switch to Body and paste your JSON payload.
Hit Send and read the status, timing and payload in the response panel.
Open Code and copy a cURL, fetch or Python snippet straight into your project.

Who It Is For

Role	Typical use
Marketing ops	Verify CRM, ESP and webhook endpoints before wiring an automation.
Developers	Reproduce a failing call, then export a working snippet.
AI / agent builders	Confirm an API's real response shape before describing it in a tool schema or GPT Action.
QA and support	Check status codes and headers without installing anything.

Pairs Well With Our Other Free Tools

GPT Connector Generator — turn a verified API into an OpenAPI 3.1 schema for a custom GPT Action.
MCP Server Tester — inspect and invoke tools on any public Model Context Protocol server.
SSL / Certificate Inspector — confirm the certificate behind the API host is valid and not about to expire.
DNS Health Checker — rule out DNS issues when an endpoint is unreachable.

FAQs

Do I need an account?

No. Sending requests, exporting code and browsing your local history are all free and login-free. An account is only needed if you want to save requests into collections.

Can I call an API on localhost?

No — private and local addresses are blocked for security. Use a locally installed client for that, or expose a public HTTPS tunnel.

Are my tokens stored?

Auth values are used to build the request and are not persisted unless you explicitly save the request to a collection while signed in.

Is there a size or time limit?

Yes: 15 seconds per request and 1 MB per response, which covers virtually all JSON APIs.

Try It

Open the API Tester and send your first request — the default example returns a live GitHub repository payload so you can see the whole flow in one click.