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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 Response Viewer?
An API response viewer sends a request and displays the response in a clean, formatted, collapsible view - easy to read and explore.
Why does API Response Viewer matter?
A readable, structured view of what the API returned, including status and headers. The request does reach the target server, and browser CORS rules may block some calls.
How is API Response Viewer calculated?
You give a URL (and method/headers), it fetches from that server in your browser and pretty-prints the JSON or text response.
What are common api response viewer mistakes?
Expecting non-CORS APIs to load from a browser.
When should you use the API Response Viewer?
Use it to inspect an API response, explore nested JSON, or share a formatted result.

What is the API Response Viewer?

An API response viewer sends a request and displays the response in a clean, formatted, collapsible view - easy to read and explore.

How the API Response Viewer works

You give a URL (and method/headers), it fetches from that server in your browser and pretty-prints the JSON or text response.

Common mistakes to avoid

  • Expecting non-CORS APIs to load from a browser.
  • Exposing secret keys in the request.
  • Mistaking a CORS block for a server error.

Keywords: api, response, rest, viewer.

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 Response Viewer 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 Response Viewer?+

API Response Viewer uses the standard api response viewer 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 Response Viewer runs entirely in your browser. Nothing is uploaded or saved to a server.

Can I use the API Response Viewer 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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Share-to-grow kit (Reddit, LinkedIn, Medium)
Reddit post
Title: I built/used this free api response viewer — instant, no signup

Body: Send REST requests and inspect the response — alias of API Tester. Try it: https://freetoolsgalaxy.com/tools/api-response-viewer
LinkedIn post
API Response Viewer on Free Tools Galaxy — Send REST requests and inspect the response — alias of API Tester. https://freetoolsgalaxy.com/tools/api-response-viewer
Medium intro
# API Response Viewer — the free tool I keep coming back to

Send REST requests and inspect the response — alias of API Tester.

Try it: https://freetoolsgalaxy.com/tools/api-response-viewer
Quora answer
The fastest way is to use a free in-browser api response viewer: https://freetoolsgalaxy.com/tools/api-response-viewer. Send REST requests and inspect the response — alias of API Tester.

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-response-viewer?embed=1" title="API Response Viewer" 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-response-viewer" target="_blank" rel="noopener">Powered by API Response Viewer 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-response-viewer?embed=1" title="API Response Viewer" 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 Response Viewer — free online tool](https://freetoolsgalaxy.com/tools/api-response-viewer)

<iframe src="https://freetoolsgalaxy.com/tools/api-response-viewer?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-response-viewer" target="_blank" rel="noopener">Try the free API Response Viewer</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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