HMAC Checker
Compute HMAC-SHA-256 and other signatures, and verify webhook signatures — locally in your browser.
Keys and messages are never sent to a server. Everything is computed in your browser.
Line breaks and spaces are signed as-is. Re-serializing the body with different spacing or key order breaks the signature.
What is this tool?
A free HMAC calculator and checker. Compute HMAC-SHA-1/256/384/512 with text, hex or Base64 keys, then paste a published signature to verify it instantly. Presets for LINE, GitHub and Stripe webhooks are included.
How to use
- Pick a preset (or Custom) and enter the key and message.
- The signature updates automatically — copy it in hex or Base64.
- Paste an expected signature to get a match/mismatch verdict.
Use cases
- Verifying webhook signatures while developing integrations.
- Reproducing an HMAC for debugging API authentication.
- Testing key formats (UTF-8, hex, Base64) without writing code.
Notes
- All computation happens locally; secrets are never transmitted.
- SHA-1 is offered only for legacy verification — prefer SHA-256 for new integrations.
FAQ
Is my secret key safe here?
Yes. Keys and messages never leave your browser — signatures are computed locally with the Web Crypto API.
Which webhook providers are preset?
LINE Messaging API, GitHub and Stripe webhooks, each with the correct algorithm, key format and signature format preselected. A custom mode covers everything else.
Why does my signature not match?
Sign the raw request body exactly as received — re-serializing JSON with different spacing or key order produces a different signature. For Stripe, the payload is timestamp.body; the tool joins it automatically.
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