API Builder - Free Online Tool | PivaBox

Build API request payloads for Claude/GPT

API Builder — Design and Test REST API Endpoints Interactively

  1. Define your API endpoint: set the HTTP method (GET, POST, PUT, PATCH, DELETE), enter the base URL and path, and add query parameters, headers, and request body as needed. The builder supports JSON, form-encoded, and multipart request bodies.
  2. Configure authentication, headers (Authorization, Content-Type, custom headers), and the request payload. The tool includes common header presets for REST APIs, GraphQL endpoints, and webhook testing.
  3. Send the request and inspect the response: status code, response headers, and formatted response body with JSON syntax highlighting. Debug API integrations by iterating on request parameters and seeing live responses.

Frequently Asked Questions

Is the API Builder free?

Yes, completely free. Test and debug as many API endpoints as you need — ideal for API development, integration testing, and learning REST concepts.

Are my API requests sent through any server?

API requests are sent directly from your browser to the target endpoint using the Fetch API. They do not pass through any intermediary server. However, the target API server will see your request as coming from your IP address — this is standard browser behavior.

What are REST API best practices for designing clean endpoints?

REST API design principles: (1) Use nouns for resources, not verbs: /users not /getUsers. HTTP methods already describe the action (GET=fetch, POST=create, PUT=replace, PATCH=update, DELETE=remove). (2) Use plural nouns consistently: /users/123 not /user/123. (3) Nest related resources: /users/123/orders for a user's orders. (4) Use query parameters for filtering, sorting, and pagination: /users?role=admin&sort=name&page=2. (5) Return proper HTTP status codes — 200 for success, 201 for creation, 204 for no-content, 400 for bad input, 404 for not found. (6) Include error details in the response body: {"error": "validation_failed", "details": [{"field": "email", "message": "Invalid format"}]}. (7) Version your API: /v1/users or use header-based versioning. (8) Use JSON for request and response bodies — it's the universal standard. (9) Always use HTTPS in production; never send API keys or tokens over plain HTTP.