HMAC Generator
LiveGenerate HMAC-SHA256, HMAC-SHA512 digests online with a secret key.
Understanding HMAC Message Authentication
HMAC (Hash-based Message Authentication Code) combines a cryptographic hash function with a secret key to produce an authentication tag that verifies both data integrity and authenticity. Unlike a plain hash that anyone can compute, an HMAC requires knowledge of the secret key — meaning only parties who share the key can generate or verify the tag. HMAC is used extensively in API authentication (webhook signatures from Stripe, GitHub, Twilio), session token generation, message verification in distributed systems, and any scenario where you need to prove a message was not altered and came from a trusted source.
Use this free HMAC generator to create HMAC digests using SHA-256, SHA-384, or SHA-512 algorithms online. Enter your message and secret key to produce a secure HMAC hash. Supports HMAC-SHA256, HMAC-SHA512, and HMAC-SHA384 for API authentication, webhook verification, and data integrity checks. All computation runs in your browser — your secret key is never sent to any server.
The Devkitr HMAC Generator computes HMAC digests using SHA-256, SHA-512, SHA-1, or MD5 hash functions with your specified secret key. Enter the message and secret key to produce the keyed hash used for webhook signature verification, API authentication, and message integrity checking. The computation runs entirely in your browser so your secret key is never transmitted.
In a typical development workflow, HMAC Generator becomes valuable whenever you need to generate hmac-sha256, hmac-sha512 digests online with a secret key. Whether you are working on a personal side project, maintaining production applications for a company, or collaborating with a distributed team across time zones, having a reliable browser-based generation tool eliminates the need to install desktop software, write one-off scripts, or send data to third-party services that may log or retain your information. Since HMAC Generator processes everything locally on your device, your data stays private and your workflow stays uninterrupted — open a browser tab, paste your input, get your result.
Key Features
Multiple Hash Algorithms
Compute HMAC using SHA-256 (most common), SHA-512 (stronger), SHA-1 (legacy), or MD5 (legacy) to match the algorithm required by your integration partner.
Hex and Base64 Output
Display the HMAC result in hexadecimal or Base64 encoding to match the format expected by different webhook providers and API authentication schemes.
Key Privacy
Your secret key never leaves the browser. All HMAC computation uses the Web Crypto API locally, keeping your signing keys confidential.
Webhook Signature Verification
Paste a received webhook body and your shared secret to compute the expected signature, then compare with the signature header to verify authenticity.
How to Use HMAC Generator
Enter Your Message
Paste the message body, webhook payload, or data string you want to authenticate with HMAC.
Provide the Secret Key
Enter the shared secret key used for HMAC signing — this is the key provided by your webhook provider or configured in your application.
Select the Algorithm
Choose the HMAC hash function — SHA-256 is standard for most modern integrations, SHA-512 for stronger security, SHA-1 for legacy systems.
Compare or Copy
Compare the computed HMAC against a received signature header, or copy the result for use in API authentication headers.
Use Cases
Verifying Stripe Webhook Signatures
Compute HMAC-SHA-256 of a Stripe webhook body with your Stripe signing secret to verify the signature matches the Stripe-Signature header.
Signing API Requests
Generate HMAC signatures for API requests that require message-level authentication, such as AWS Signature V4 or other HMAC-based auth schemes.
Validating GitHub Webhooks
Compute HMAC-SHA-256 of the webhook payload body with your GitHub webhook secret and compare against the X-Hub-Signature-256 header.
Implementing Message Integrity Checks
Generate HMAC tags for messages in distributed systems to verify they were not modified in transit between services.
Pro Tips
Always use constant-time comparison when verifying HMAC signatures — standard string equality is vulnerable to timing attacks that leak partial match information.
Use HMAC-SHA-256 for new integrations. SHA-1 and MD5 based HMACs are weaker and only justified for backward compatibility with existing systems.
Store HMAC secret keys in environment variables or secret managers — never hardcode them in source code or commit them to version control.
When debugging signature mismatches, check for whitespace differences, encoding issues, and whether the raw body or parsed JSON is being signed.
Common Pitfalls
Using a plain hash (SHA-256 without key) instead of HMAC for authentication
Fix: Plain hashes cannot verify sender identity because anyone can compute them. HMAC requires the secret key, ensuring only authorized parties can create valid signatures.
Comparing HMAC signatures with standard string equality (==)
Fix: Use crypto.timingSafeEqual() or equivalent constant-time comparison. Regular equality is vulnerable to timing side-channel attacks.
Signing parsed JSON instead of the raw request body
Fix: JSON parsing and re-serialization may change whitespace, key order, or Unicode escapes. Always compute HMAC over the raw, unmodified request body bytes.
Frequently Asked Questions
QHow do I generate HMAC-SHA256 online?
Enter your message text and secret key, select SHA-256 as the algorithm, and the HMAC generator instantly produces your HMAC-SHA256 digest.
QWhat HMAC algorithms are supported?
HMAC-SHA256, HMAC-SHA384, and HMAC-SHA512. SHA-256 is the most commonly used for API authentication and webhook verification.
QWhat is HMAC?
HMAC (Hash-based Message Authentication Code) combines a cryptographic hash function with a secret key to provide both data integrity and authentication.
QIs my secret key safe in this HMAC generator?
Yes. All HMAC computation happens in your browser using the Web Crypto API. Your secret key is never transmitted to any server.
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