Question 1

Why do some API requests fail with a 'CORS Error' in a browser-based tester?

Accepted Answer

Cross-Origin Resource Sharing (CORS) is a browser security mechanism that restricts web applications from making HTTP requests to a domain different from the one serving the web page. If the destination server does not include the 'Access-Control-Allow-Origin' header permitting cross-origin browser requests, your browser will block the response for security reasons, even though the server may have processed the request successfully. Desktop tools (like Postman or curl) bypass this because they are not constrained by browser sandboxes.

Question 2

What is the difference between PUT and PATCH in RESTful design?

Accepted Answer

PUT is an idempotent method designed to replace the entire target resource with the provided payload. If you omit fields in a PUT request, those fields should either be deleted or reset to null. In contrast, PATCH applies a partial update: you only supply the specific fields you wish to modify, leaving all other existing properties untouched.

Question 3

What does 'Idempotency' mean in HTTP methods?

Accepted Answer

An HTTP method is considered idempotent if executing the identical request multiple consecutive times produces the exact same result on the server state as executing it once. GET, HEAD, PUT, and DELETE are strictly idempotent. POST is non-idempotent because submitting a POST request multiple times will create multiple distinct records or trigger duplicate financial transactions.

Question 4

What is the difference between 401 Unauthorized and 403 Forbidden status codes?

Accepted Answer

A 401 Unauthorized status indicates that authentication is missing or invalid (i.e. 'I don't know who you are; please log in or provide a valid API key'). A 403 Forbidden status indicates that authentication was recognized, but the authenticated user lacks sufficient permissions to access the resource (i.e. 'I know who you are, but you are not allowed to view this resource').

Question 5

How do I pass an Authorization Bearer token in an HTTP header?

Accepted Answer

To pass a token (such as a JWT or OAuth 2.0 access token), add an 'Authorization' header with the value 'Bearer YOUR_TOKEN_STRING'. The word 'Bearer' must be separated from the token string by a single space.

Question 6

What is an HTTP Preflight (OPTIONS) request?

Accepted Answer

When a browser makes a 'complex' cross-origin request (e.g. using methods other than GET/POST or adding custom headers like 'Authorization'), the browser automatically sends an HTTP OPTIONS request before the actual request. The server must respond with appropriate CORS headers indicating allowed methods and headers before the browser will proceed with the real request.

Question 7

What is the difference between URL Query Parameters and Request Body?

Accepted Answer

Query parameters are key-value pairs appended directly to the URL after a '?' symbol (e.g. '?page=2&limit=20') and are typically used with GET requests for filtering and pagination. The Request Body carries arbitrary structured payloads (such as JSON, XML, or multipart form data) in the HTTP payload body, typically used with POST, PUT, and PATCH requests.

Question 8

What are the most common Content-Type headers used in web APIs?

Accepted Answer

The most common Content-Type headers are: (1) 'application/json' for standard REST JSON payloads; (2) 'application/x-www-form-urlencoded' for standard HTML form submissions; (3) 'multipart/form-data' for uploading files and binary assets; and (4) 'application/xml' or 'text/plain' for legacy and raw string formats.

Question 9

What is the purpose of the 429 Too Many Requests status code?

Accepted Answer

Status 429 indicates that the client has exceeded the server's rate limits (e.g. sending more than 100 requests per minute). Servers often include a 'Retry-After' header indicating how many seconds the client must wait before making another request.

Question 10

Can I test webhook endpoints with this online API client?

Accepted Answer

Yes. You can paste your webhook receiver URL (such as a Stripe, GitHub, or Slack webhook handler), set the method to POST, provide sample JSON webhook event payloads, and inspect whether your server responds with an HTTP 200/204 acknowledgment status.

Method	Safe?	Idempotent?	Request Body Allowed?	Primary Purpose & Behavior
GET	Yes	Yes	No	Retrieves representation of a resource. Must never modify server state.
POST	No	No	Yes	Submits data to create a new resource or execute complex operations.
PUT	No	Yes	Yes	Replaces the entire target resource with the new request representation.
PATCH	No	Usually	Yes	Applies partial modifications to specific fields of an existing resource.
DELETE	No	Yes	Optional	Removes the specified resource from the server.

Header Name	Type	Standard Usage Example
Content-Type	Request / Response	application/json; charset=utf-8
Authorization	Request	Bearer eyJhbGciOi...
Accept	Request	application/json, text/plain, /
Access-Control-Allow-Origin	Response (CORS)	* or https://tooleka.com
Cache-Control	Response	no-cache, no-store, max-age=0, must-revalidate

API Request Tester

Understanding the HTTP Request-Response Cycle (RFC 9110)

Why Browser-Based API Testing Matters

Complete Guide to HTTP Methods (Verbs)

HTTP Response Status Codes Reference

2xx — Success

3xx — Redirection

4xx — Client Errors

5xx — Server Errors

Essential HTTP Headers & Cross-Origin (CORS) Mechanics

💡 Understanding CORS in Browser-Based API Testing

Frequently Asked Questions About API Request Testing

Frequently Asked Questions