How does HMAC differ from a plain hash?

Anyone can compute a plain hash; HMAC mixes in a secret key, so only key holders can produce a valid signature — which enables authentication.

How do I troubleshoot a signature mismatch?

Check in order: is the key correct, was the message URL-encoded or sorted, do line breaks match, and has the timestamp expired.

HMAC Generator

Free online HMAC calculator for HMAC-SHA1/256/512: enter key and message to generate a MAC for API signature checks.

Privacy: all processing happens locally in your browser. Your input never leaves your device.

What is HMAC Generator?

HMAC is a message authentication code computed with a secret key: it verifies both data integrity and the sender's identity, and is widely used for API signing on open platforms (such as payment gateways and AWS SigV4). When signatures do not match during integration, enter the same key and message here and compare byte by byte — you will quickly find whether the key, the encoding or the concatenation order is wrong.

How to Use

Enter the key and the message to sign
Choose the algorithm (SHA1/256/512)
Compare or copy the hexadecimal signature

FAQ

How does HMAC differ from a plain hash?: Anyone can compute a plain hash; HMAC mixes in a secret key, so only key holders can produce a valid signature — which enables authentication.
How do I troubleshoot a signature mismatch?: Check in order: is the key correct, was the message URL-encoded or sorted, do line breaks match, and has the timestamp expired.

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Last updated 2026-09-04