API Request Builder – Free Online API Tester

Tool Vera Lab Team
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API Request Builder

Build, send and test HTTP API requests directly in your browser.

Ready to send request
Request Configure your API request
Query Parameters Add parameters to your request URL.
Request Headers Add custom HTTP headers.
Request Body Use JSON for POST, PUT and PATCH requests.
Response API server response
No response
Status —
Time —
Size —
No response headers yet.
Response Body 
Send a request to see the API response.
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Browser-based API testing

Some APIs may block browser requests because of CORS security policies. This is controlled by the API server and cannot be bypassed by this tool.

How Does the API Request Builder Work?

API Request Builder is a free online tool that helps developers test HTTP API requests directly from their web browser. You can select the HTTP method, enter an API URL, add query parameters and request headers, provide a JSON request body, and then send the request to view the server response.

The tool uses the browser's built-in Fetch API to communicate with the selected API endpoint. When the server allows browser requests, the tool displays the response status, response headers, response time, response size, and response body.

How to Use the API Request Builder

  1. Select the HTTP method you want to use, such as GET, POST, PUT, PATCH, or DELETE.
  2. Enter the complete API endpoint URL.
  3. Add Query Parameters if your API requires them.
  4. Add custom HTTP Headers when required by the API.
  5. For POST, PUT, or PATCH requests, enter your JSON data in the Request Body section.
  6. Click Send Request.
  7. Review the response status, response time, headers, and returned data.

Key Features

HTTP Methods Supports GET, POST, PUT, PATCH and DELETE requests.
Query Parameters Easily add and manage URL query parameters.
Custom Headers Add authorization, content type and other headers.
JSON Body Create and format JSON request data.
Response Details View status code, response headers and response body.
Response Timing See approximately how long the request took.
Response Size View the approximate size of returned response data.
JSON Formatting Automatically format readable JSON responses.

Who Can Use This Tool?

API Request Builder can be useful for web developers, mobile app developers, students, software engineers, API developers, and anyone who needs to inspect or test an HTTP API endpoint.

  • Testing REST API endpoints
  • Checking API responses
  • Testing JSON requests
  • Debugging API parameters
  • Inspecting response headers
  • Learning how HTTP APIs work
  • Testing public APIs during development

Important Note About CORS

Some APIs cannot be tested directly from a browser because their servers do not allow cross-origin requests. This restriction is called CORS (Cross-Origin Resource Sharing).

When an API blocks browser requests, the browser may prevent this tool from accessing the response. This is a security feature controlled by the API server and cannot be bypassed by JavaScript running on a normal web page.

Frequently Asked Questions (FAQ)

What is an API Request Builder?

An API Request Builder is an online tool that allows developers to create and send HTTP requests to API endpoints and inspect the returned response.

Is API Request Builder free?

Yes. This online API Request Builder is free to use and does not require a paid subscription.

Which HTTP methods are supported?

The tool supports GET, POST, PUT, PATCH and DELETE requests.

Can I send JSON data?

Yes. You can enter JSON data in the Request Body section and use it with methods such as POST, PUT and PATCH.

Why am I getting a CORS error?

A CORS error usually means that the API server does not allow requests from web browsers. This is a server-side security policy and cannot be disabled by this tool.

Can I add custom API headers?

Yes. You can add custom request headers such as Content-Type and other headers supported by the target API.

Does the tool store my API requests?

The tool is designed to process requests directly in your browser. Your API data is not intentionally stored by the tool itself.

Can I test private APIs?

You can test APIs that are accessible from your browser and that permit the required authentication and cross-origin requests. Some private APIs may require additional authentication or server-side access.

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