HMAC Generator

How to Use the Free Client-Side HMAC Generator

HMAC takes a message and a shared secret key and produces a signature that proves both integrity and authenticity. This generator computes three variants at once using the Web Crypto API, entirely within your browser.

1. Enter the message you want to sign.
2. Provide a secret key known only to you and the intended receiver.
3. Select HMAC-SHA256, HMAC-SHA384, or HMAC-SHA512.
4. Click any generated signature to copy it for use in your application.

When to Use HMAC Generator

HMAC is the workhorse of authenticated messaging. Webhook providers sign every delivery with a keyed hash so that you can verify the payload really came from them and was not tampered with in transit. This tool is ideal for computing or checking those signatures during integration, for signing inter-service messages in a microservice architecture, and for generating the keyed digests used inside OAuth flows and JWT signing contexts.

The simultaneous output of all three algorithms is a small convenience with real payoff. When you are diagnosing a signature mismatch, seeing SHA-256, SHA-384, and SHA-512 side by side lets you confirm your server is using the same variant as the caller, which is a surprisingly common source of 403s and invalid-signature errors.

HMAC Generator Tips and Best Practices

1. Use a cryptographically random secret of at least 256 bits. HMAC's strength rests entirely on the secrecy and quality of the key, so an empty or guessable key turns the signature into theater.
2. Understand what HMAC does and does not do. It proves authenticity and integrity, but the message itself stays readable, so never assume a signed payload is encrypted.
3. Store secret keys in environment variables or a key manager. Hardcoding them in code or committing them to version control is how signing secrets leak.
4. Stick with SHA-256 or SHA-512. The SHA-1 variants are deprecated for security-sensitive applications, so avoid them in anything headed to production.

Why Client-Side Privacy Matters for signing messages and verifying their authenticity

The whole point of HMAC is that only parties sharing a secret can produce a valid signature. If you paste that secret into a server-based generator to compute a signature, the secret is compromised the moment it leaves your browser, and the authenticity guarantee evaporates.

This generator performs every hash locally. Your message and secret key never leave your device, no server sees either value, and the signature you copy out is produced by code running entirely in your own browser.