Webhook HMAC Signer
Sign and verify GitHub, Stripe, and Slack webhook signatures locally.
OpenTest REST API endpoints. - runs entirely in your browser. Free, fast and private.
Choose GET/POST/PUT and enter the endpoint address.
Configure auth headers, query params, and JSON body.
The browser calls the API and captures the response.
Status, headers, and formatted body appear for review.
API Tester is a free api toolkit utility on OneDevToolkit. Test REST API endpoints. It runs in your browser for this session - use the workspace on this page to try it.
Need a related step? Open the API Toolkit hub at /api-tools/ or the <a href="/blog/">blog</a> for longer workflows.
Processes data instantly with no server round-trips.
Your data never leaves your browser. Nothing is uploaded.
Works in any modern browser. Nothing to download or install.
No limits, no sign-up, no credit card required.
Works on desktop, tablet and mobile devices.
Beautiful in both themes. Your preference is saved.
Keyboard shortcut
Use API Tester to format, validate, or transform data while debugging or reviewing a PR.
Keep payloads on your device - no upload farm between you and the result.
Chain related code tools in Recipe Studio when you need multi-step transforms.
Answers for this tool. For site-wide help, open the FAQ hub.
API Tester Test REST API endpoints. It runs entirely in your browser with instant feedback.
No server upload is required for formatting/validation. Clearing the page removes the text from memory.
Validators report problems; formatters beautify valid structure. Severely broken input may need manual fixes first.
Formatters and converters aim to preserve meaning. Always review diffs for mission-critical code before committing.
Paste smaller chunks if the tab slows down. Minifiers and deep validators scale with input size on the CPU you have.
Many tools support Ctrl/⌘+Enter to run and standard copy shortcuts. Check the tool toolbar for Sample / Clear / Download.
When options exist (spaces vs tabs, indent width), set them before copying output into your repo to match project style.
After the page loads, formatting continues offline. CDN libraries need an initial network load.
Bookmark API Tester, copy output into editors, or chain steps with Recipes.