🔌 API Tester

Send HTTP requests and inspect responses. A browser-based API client, like a mini Postman.

Last updated: May 18, 2026 · By Λ

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Note: This tool runs entirely in your browser using the fetch() API. Due to CORS (Cross-Origin Resource Sharing) restrictions, some APIs may block requests from web pages. If a request fails, the target server may not allow cross-origin requests. Public APIs and APIs with permissive CORS headers will work fine. For restricted APIs, consider using a dedicated API client or a CORS proxy.

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Free Browser-Based API Tester

Test HTTP APIs directly in your browser with this lightweight API client. Supports GET, POST, PUT, PATCH, DELETE, HEAD, and OPTIONS methods. Add custom headers, set request bodies (JSON, form data, or raw text), and configure authentication (Bearer token or Basic Auth). View response status codes, headers, timing, and body content with JSON syntax highlighting. Request history is saved locally so you can quickly re-send previous requests. Every call is a fetch() issued straight from your own browser to the API you target, so nothing you type here passes through or gets stored on a BoltQuickTools server. No account or installation required.

What is an API Tester?

An API tester is a tool that lets you send HTTP requests to web APIs and inspect the responses you get back. APIs (Application Programming Interfaces) are the backbone of modern software, allowing different services and applications to communicate with each other over the internet. When you build or integrate with an API, you need a way to quickly test endpoints, verify response data, and debug issues without writing code every time. This browser-based API tester gives you that ability instantly, with no downloads or sign-ups required.

Developers, QA engineers, and technical project managers all benefit from having a lightweight API testing tool on hand. Whether you are prototyping a new integration, verifying that a REST endpoint returns the correct data, or troubleshooting authentication issues, this tool handles it directly in your browser. Unlike desktop applications such as Postman or Insomnia that require installation and account creation, this online API tester is ready to use the moment you open the page. Your requests are made from your browser using the Fetch API, and your request history is stored locally so you can revisit previous calls without any cloud storage.

How to Use This Tool

Select the HTTP method (GET, POST, PUT, PATCH, DELETE, HEAD, or OPTIONS) from the dropdown menu on the left.
Enter the full API endpoint URL in the text field, including the protocol (for example, https://api.example.com/users).
Optionally add custom headers, a request body (JSON, form data, or raw text), and authentication credentials (Bearer token or Basic Auth) using the tabs below the URL bar.
Click "Send" to execute the request. The response status code, headers, timing information, and body content will appear in the response section below, with automatic JSON syntax highlighting for readable output.

Key Features

Seven HTTP Methods - Full support for GET, POST, PUT, PATCH, DELETE, HEAD, and OPTIONS requests, covering all standard REST API operations.
Custom Headers - Add as many request headers as you need with an intuitive key-value editor, plus a dropdown for commonly used headers like Content-Type and Authorization.
Multiple Body Formats - Send request bodies as JSON, form data, or raw text. The editor supports syntax-aware input for structured data.
Built-in Authentication - Configure Bearer token or Basic Auth credentials without manually building authorization headers.
Request History - Previous requests are saved locally in your browser, allowing you to quickly resend or modify past API calls without retyping everything.

Frequently Asked Questions

Is my data safe when using this API tester?

Yes. All requests are sent directly from your browser to the target API. No data passes through any intermediary server. Your request history, headers, and credentials are stored only in your browser's local storage and never transmitted to BoltQuickTools or any third party.

Why do some API requests fail with a CORS error?

Because this tool runs in your browser, it is subject to CORS (Cross-Origin Resource Sharing) restrictions. If the target API server does not include the appropriate CORS headers in its response, your browser will block the request. This is a browser security feature, not a limitation of this tool. APIs designed for public consumption typically include CORS headers, but internal or private APIs may not.

Can I test APIs that require authentication?

Absolutely. The tool supports Bearer token authentication and Basic Auth (username and password). You can also manually add any custom authorization header in the Headers tab if you use a different authentication scheme like API keys or OAuth tokens.

How does this compare to Postman or other API testing tools?

This tool is designed for quick, lightweight API testing directly in your browser. It covers the most common use cases such as sending requests, inspecting responses, and managing headers. For advanced features like automated test suites, environment variables, and team collaboration, dedicated desktop applications may be more appropriate. However, for everyday debugging and exploration, this browser-based tool is faster to access and requires no setup.