Free Online API Tester
Test APIs online by sending HTTP requests, viewing responses, checking headers, and debugging endpoints directly from your browser.
Select a body type and enter request payload.
Quick auth helper (adds Authorization header).
Use variables as {{name}} in URL, headers, params, auth, and body.
Preview uses a blob URL in your browser. HTML is sandboxed (scripts disabled); treat remote HTML like untrusted content.
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Requests are sent directly from your browser (CORS applies). Do not send secrets on untrusted networks.
What this API tester is built for
Test an API in four steps
Pick the verb, paste the endpoint, and keep secrets out of shared screens.
Add query rows, header presets or JSON import, then raw JSON or form modes as needed.
Review status, response body, and response headers; format JSON when the API returns it.
Copy the body, download a snapshot, or keep the tab in a collection for the next run.
When to use this tool
When this API tester is ideal
- Quick checks on a single endpoint or variant.
- Frontend debugging when CORS allows the call from this origin.
- Validating JSON shape, headers, and status codes on real responses.
- Smoke tests without installing a desktop API client.
When a full API client is better
- Large collections, folders, and shared environments.
- Team collaboration, comments, and history across workspaces.
- Automated test suites, runners, and CI pipelines.
- Complex OAuth flows, chained requests, or mock servers.
Continue your workflow
Export API responses into spreadsheet-friendly rows.
Stage response objects as INSERT-ready SQL text.
Hand payloads to partners that expect XML trees.
Build JSON bodies from grid edits before you send.
Preview structured data as an HTML table fragment.
Normalize XML feeds for JSON-first clients.
Overview & guides
This workspace is a lightweight, browser-based client: one active request tab, collections on the left, and a response panel below. Nothing runs on ConversionTab servers—your URL, headers, and body leave directly from the browser (subject to CORS).
Use it when you need a fast loop: tweak URL or JSON, send, read the body, repeat.
The request builder merges method, URL, query rows, enabled headers, auth helper output, and body into one fetch. The response panel shows HTTP status, elapsed time, response headers as JSON, and the raw body—use Format response when the body is JSON.
If the browser blocks the call, the error is usually CORS: the target API must allow this origin, or test from an extension-backed client instead.
- Sending production tokens in a shared screen—use short-lived test keys.
- Forgetting
Content-Type: application/jsonon JSON POST bodies. - Assuming CORS errors mean the API is down—they often mean the API did not allow browser origins.
- Pasting huge payloads without trimming—start small, then scale.
Are requests logged on your servers? They are issued from your browser; we do not proxy them through our backend.
Can I import Postman collections? Use Import collection or paste collection JSON when the format matches what the tool expects.
Why is Send disabled? Enter a valid URL first; the button enables when the field looks like a real HTTP(S) endpoint.