API Request Builder

Build HTTP requests visually with method, headers, body, and params. Send via fetch and see the full response. Like a mini Postman.

How to Use API Request Builder

1

Choose HTTP method

Select GET, POST, PUT, DELETE, or another HTTP method.
2

Enter the endpoint URL

Type the full API URL including any path parameters.
3

Add headers and body

Set authorization headers, content type, and request body as needed.
4

Copy the request

Export the formatted request as cURL, fetch, or your preferred format.

Tested tool guide Tested browser tools Checked August 16, 2026

What API Request Builder does and how it behaves

This tool gives you fields for an HTTP method, URL, query parameters, headers, and a request body, then fires the request using your browser's fetch and renders the status code, response headers, and body it gets back. Because the request leaves from your browser tab rather than a desktop app or server, the most common surprise is CORS: if the target API doesn't send an Access-Control-Allow-Origin header permitting this page's origin, the browser blocks you from reading the response even when the server processed the request successfully.

How the result is produced

Assembling the request

Method, URL, a key-value table for query parameters, a key-value table for headers, and a body editor (raw text or JSON) are combined into a single outgoing request. Query params you add are URL-encoded and appended to the URL automatically, so you don't hand-build the query string.

Sending and reading back the response

The request is sent with the browser's built-in fetch. The tool reports the resolved status code and status text, lists every response header the browser exposes, and pretty-prints the body if it parses as JSON, otherwise shows it as plain text. Network failures and CORS blocks surface as a generic fetch error rather than a detailed cause, since browsers don't expose that detail to scripts.

Good uses

Trying a REST endpoint's shape (status, headers, JSON structure) while writing client code against it, without installing Postman or Insomnia
Reproducing a fetch call from your app in isolation to see whether the problem is your request or the server's response
Checking quickly, from a machine where you can't install a desktop API client, whether an endpoint is reachable and what it returns

Limits and checks

CORS is enforced by the browser, not by this tool: an API with no Access-Control-Allow-Origin for this page's origin will fail here even though the same request works from curl, Postman, or your server code
Fetch cannot set certain headers regardless of what you type in the headers table - Origin, Cookie, Host, Referer, and a few others are forbidden request headers per the Fetch spec and are silently dropped by the browser
Anything you enter, including API keys or bearer tokens in an Authorization header, is visible in the browser's network tab and page memory - there's no separate credential vault or masking

Common questions

Can I test endpoints that need an API key or bearer token?

Yes - add it as a header, typically Authorization: Bearer <token>, in the headers table before sending. The tool doesn't run an OAuth flow for you or store the token between visits; you supply and re-supply it yourself.

Why did I just get "Failed to fetch" with no other detail?

That's almost always a CORS rejection or a plain network failure (wrong URL, offline, mixed-content HTTPS-to-HTTP block). Browsers intentionally withhold the specific cause from JavaScript, so check the browser console's network tab for the real reason.

References and verification

The behavioral notes were checked against the browser implementation. Standards and primary references below define the relevant format, formula, or platform behavior.