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100% free · no signupRuns in your browser

API Tester

In-browser REST client: send GET/POST/PUT/PATCH/DELETE with custom headers and body.

Best for: Use it to try an API endpoint, debug a webhook, or check a response quickly.

Complete guide

Input

How it's calculated & sources
The API Tester uses the standard, deterministic formula, so the same inputs always produce the same result. It runs entirely in your browser, so your inputs are never uploaded. Last reviewed June 2026.

Free & no sign-up · runs entirely in your browser. Results are estimates for general information, not professional advice — verify important decisions with a qualified expert. Last reviewed June 2026.

How it works

Calls the URL using the browser fetch() API. Subject to CORS — the target server must allow your origin.

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Complete guide

Quick answers

Short, sourced answers to the questions people (and AI assistants) ask most.

What is API Tester?
An API tester sends HTTP requests (GET, POST, etc.) to a URL and shows the response status, headers and body - a lightweight Postman in your browser.
Why does API Tester matter?
The server's actual response - status code, headers and body. Note the request DOES go to the target server (as any HTTP client would); cross-origin (CORS) rules may block some calls from a browser.
How is API Tester calculated?
You set the method, URL, headers and body, and the tool sends the request from your browser to that server and displays what comes back.
What are common api tester mistakes?
Expecting requests to non-CORS-enabled APIs to work from a browser.
When should you use the API Tester?
Use it to try an API endpoint, debug a webhook, or check a response quickly.

What is the API Tester?

An API tester sends HTTP requests (GET, POST, etc.) to a URL and shows the response status, headers and body - a lightweight Postman in your browser.

How the API Tester works

You set the method, URL, headers and body, and the tool sends the request from your browser to that server and displays what comes back.

Common mistakes to avoid

  • Expecting requests to non-CORS-enabled APIs to work from a browser.
  • Putting secret API keys somewhere they could be exposed.
  • Confusing a CORS block with a real server error.

Keywords: api, rest, http, fetch, postman.

The request is sent to the URL you enter (like any HTTP client); the tool itself stores nothing.

Reviewed by the Free Tools Galaxy editorial team · Updated June 2026 · Calculated privately in your browser.

Frequently asked questions

Is the API Tester free to use?+

Yes. Every tool on Free Tools Galaxy is 100% free, runs in your browser and requires no signup.

How accurate is the API Tester?+

API Tester uses the standard api formula in double-precision arithmetic, so the same inputs always produce the same result and you can verify any figure by hand. It is an educational estimate — real-world outcomes depend on your actual rates, rules and assumptions.

Do you store my inputs?+

No. The API Tester runs entirely in your browser. Nothing is uploaded or saved to a server.

Can I use the API Tester on mobile?+

Yes — the interface is fully responsive and works on phones, tablets and desktops.

What are common mistakes to avoid?+

The most frequent mistake is mixing units. Double-check your inputs use a single, consistent unit before clicking Calculate.

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Reddit post
Title: I built/used this free api tester — instant, no signup

Body: In-browser REST client: send GET/POST/PUT/PATCH/DELETE with custom headers and body. Try it: https://freetoolsgalaxy.com/tools/api-tester
LinkedIn post
API Tester on Free Tools Galaxy — In-browser REST client: send GET/POST/PUT/PATCH/DELETE with custom headers and body. https://freetoolsgalaxy.com/tools/api-tester
Medium intro
# API Tester — the free tool I keep coming back to

In-browser REST client: send GET/POST/PUT/PATCH/DELETE with custom headers and body.

Try it: https://freetoolsgalaxy.com/tools/api-tester
Quora answer
The fastest way is to use a free in-browser api tester: https://freetoolsgalaxy.com/tools/api-tester. In-browser REST client: send GET/POST/PUT/PATCH/DELETE with custom headers and body.

Embed this tool anywhere

Free embed code for blogs, docs and dashboards. Every embed sends a backlink home — helping you and the galaxy grow together.

HTML iframe
Drop into any site — auto-resizes to its content height, theme-aware.
<iframe src="https://freetoolsgalaxy.com/tools/api-tester?embed=1" title="API Tester" loading="lazy"
  style="width:100%;height:600px;border:0;border-radius:16px;background:#0b1020"
  allow="clipboard-write"></iframe>
<script>window.addEventListener("message",function(e){if(e.data&&e.data.type==="ftg-embed-height"){document.querySelectorAll("iframe").forEach(function(f){if(f.contentWindow===e.source){f.style.height=e.data.height+"px";}});}});</script>
<p><a href="https://freetoolsgalaxy.com/tools/api-tester" target="_blank" rel="noopener">Powered by API Tester on Free Tools Galaxy</a></p>
Responsive wrapper
Aspect-locked container — good for blog post bodies.
<div style="position:relative;padding-bottom:75%;height:0;overflow:hidden;border-radius:16px">
  <iframe src="https://freetoolsgalaxy.com/tools/api-tester?embed=1" title="API Tester" loading="lazy"
    style="position:absolute;inset:0;width:100%;height:100%;border:0" allow="clipboard-write"></iframe>
</div>
WordPress / Markdown
Paste in a custom-HTML block or markdown file.
[API Tester — free online tool](https://freetoolsgalaxy.com/tools/api-tester)

<iframe src="https://freetoolsgalaxy.com/tools/api-tester?embed=1" width="100%" height="600" frameborder="0"></iframe>
Text link-back
Minimal credit link — best for sidebars and footers.
<a href="https://freetoolsgalaxy.com/tools/api-tester" target="_blank" rel="noopener">Try the free API Tester</a>

Share-to-Grow Kit

Pre-written, ready-to-paste posts for every major channel. Help others discover this tool — and earn backlinks.

Title
I built a free pregnancy due date calculator that works instantly in the browser — no signup, no ads in your face
Body
Hey r/[subreddit],

I kept needing a quick pregnancy due date calculator and most options online were slow or behind paywalls, so I built one that:

• Runs 100% in your browser (your data never leaves your device)
• No signup, no email wall, no popups
• Loads in under a second on mobile

It covers the standard pregnancy due date use cases (pregnancy, due, date, baby) and links out to the formula + worked examples if you want to learn the math.

Link: https://freetoolsgalaxy.com/tools/pregnancy-due-date-calculator

Happy to take feedback — what's missing?
Post to a relevant subreddit (e.g. r/InternetIsBeautiful, r/webdev, r/productivity). Avoid spammy subs.
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