Application Programming Interface (API) Testing Tool

Introduction:

HTTP requests are structured messages used to read or change data on web services, and understanding them makes debugging clearer and faster. Seeing the exact request and the full response helps you confirm behavior, compare attempts, and pinpoint issues.

Uniform Resource Locators identify the target, query parameters refine the call, and headers describe preferences and context. A request body carries data for create and update actions, while the response reports status, headers, and text or binary content you can inspect.

You provide a method and a URL, then add optional parameters, headers, and a body. The result shows status and size and time, with JSON prettified and HTML rendered for quick review, so you can test a change and immediately see what improved.

A simple check might send a small JSON object and confirm the echoed fields and a successful code. Another check might replay the same call with a shorter timeout to simulate a slow path and compare the measured time.

Use disposable credentials for experiments and avoid pasting secrets that you cannot rotate quickly.

Technical Details:

HTTP request and response pairs are the observed quantities. The request includes a method, a Uniform Resource Locator (URL), headers, and optionally a body. The response exposes status code and text, headers, a decoded body when textual, the resolved URL, approximate size in bytes, and elapsed time in milliseconds.

Elapsed time is measured from dispatch to response resolution. Size is taken from the received buffer when available. Textual bodies are decoded using the charset from the Content‑Type header when present, otherwise UTF‑8. JSON is detected and pretty‑printed; HTML can be rendered in a preview.

Authentication can attach an Authorization header using Basic credentials once encoded to Base64, or a Bearer token as provided. If a body looks like JSON and no Content‑Type is set, a JSON content type is applied automatically for methods that allow a body.

Interpret results using standard HTTP status families. Success codes indicate an accepted request, redirections point to follow‑up locations, client errors suggest fixes on the caller side, and server errors indicate issues on the service side.

1. Construct the final URL by appending enabled query parameters.
2. Merge enabled headers and add Authorization for Basic or Bearer when set.
3. For methods that allow a body, attach the body text; set JSON content type if inferred.
4. Configure redirect handling and start a timer; apply an optional timeout.
5. Send the request; record status, status text, resolved URL, and headers.
6. Clone the response; read a buffer for size; decode text using the detected charset.
7. Detect JSON for pretty printing; enable HTML preview when the type is HTML.
8. Build curl‑style request and response traces for inspection and copying.

Requests run directly from the browser to the target endpoint. The API must explicitly allow your origin or the browser blocks the response. Saved requests are stored in local storage and can be exported or imported as JSON.

Calls go straight to the URL you specify and no additional services receive the request. Saved entries remain in local storage until you clear them.

• CORS must permit your origin for headers and body to be readable.
• Authentication supports Basic and Bearer only.
• JSON detection uses structure; malformed JSON is treated as text.
• Charset comes from Content‑Type; fallback is UTF‑8.
• Large bodies increase memory use and slow formatting Heads‑up.
• Elapsed time reflects response resolution, not full render of previews.
• HTML preview renders returned markup; treat untrusted content with care.
• Redirect handling follows the selected fetch mode; cookies use browser defaults.

• Blank URL triggers a local error message.
• Cross‑origin endpoints without proper headers cause blocked reads.
• Timeout aborts the request; increasing it can confirm slow paths.
• Sending a body with GET or HEAD has no effect.
• Incorrect Content‑Type can confuse server parsing.
• Wrong charset mis‑decodes text and breaks JSON parsing.
• Very large JSON slows pretty printing and copying.
• Manual redirect mode requires you to inspect Location headers.
• Basic auth exposes user and password in an easily reversible header.
• Binary responses show a size note rather than a preview.

Step‑by‑Step Guide:

HTTP API calls with request and response inspection.

1. Enter the URL of the endpoint.
2. Choose the Method that matches the action.
3. Add query parameters and headers as needed.
4. If the API blocks browser calls, adjust the server CORS policy or test from an allowed origin.
5. Provide a body for create and update methods; use JSON when appropriate.
6. Optionally set a Timeout and redirect handling.
7. Send the request and review status, size, and time.
8. Open JSON, body, preview, and trace tabs to inspect details.

Repeat with small changes to compare outcomes and confirm fixes.

FAQ:

Troubleshooting:

• Check the URL is absolute and reachable.
• Remove conflicting headers, especially duplicate content types.
• Increase the timeout for slow services.
• Switch redirect handling to error to see the status and Location.
• Pretty‑print the body to confirm valid JSON.
• Use Basic or Bearer, not both at once.
• Try the request in a separate tab to confirm server availability.

Advanced Tips:

• Tip Keep one Accept header; duplicate entries make negotiation unclear.
• Tip Save golden requests and reuse them to catch regressions quickly.
• Tip Use manual redirect mode to verify authentication on 302 responses.
• Tip Compare elapsed time before and after small header changes.
• Tip Inspect response size to spot compression or payload drift.
• Tip For Basic auth, use test accounts and rotate passwords often.

Glossary:

HTTP method

Verb that indicates the action such as GET or POST.

URL

Uniform Resource Locator that addresses the target resource.

Header

Key–value metadata attached to requests and responses.

Content‑Type

Header describing how to interpret the body.

Status code

Three‑digit code that classifies the outcome of a request.

CORS

Cross‑Origin Resource Sharing rules for browser access to responses.