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HMAC Generator

Generate HMAC signatures with SHA-1, SHA-256, SHA-384, or SHA-512 using a secret key for API authentication, webhook verification, and message integrity checks.

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Reference · overview · features · use cases · steps · examples · troubleshooting · faq

About HMAC Generator

HMAC Generator is a free browser-based tool for creating HMAC signatures from a message and a shared secret key using algorithms such as SHA-1, SHA-256, SHA-384, and SHA-512. HMAC stands for Hash-based Message Authentication Code, and it is widely used in API authentication, webhook verification, signed requests, and any workflow where two systems need to prove that a message has not been changed and came from a party that knows the secret. Unlike a plain hash, an HMAC depends on both the message and the secret key. That difference matters because it turns the hash into a verification mechanism rather than just a digest. If the message changes or the wrong secret is used, the generated signature changes too. This is why HMAC appears in many production systems including payment gateways, cloud APIs, and webhook security flows. This tool is especially useful for developers and QA teams testing authentication logic. If a webhook signature does not match, you need a fast way to reproduce the expected HMAC with the same payload and secret. If an API requires signed requests, you may want to confirm the output format before implementing the logic in code. A browser-based tool makes those checks fast. The available algorithm selection is also practical because different platforms require different HMAC variants. SHA-256 is a common modern default, but some integrations still use SHA-1 or stronger SHA-512-based signatures. When used correctly, HMAC is one of the most useful building blocks in shared-secret security design. This generator makes it easier to test, verify, and understand those flows without writing a custom script every time.

Key features.

Multiple HMAC algorithms. Generate signatures with SHA-1, SHA-256, SHA-384, or SHA-512 depending on your integration requirements.
Shared-secret signature testing. Useful for reproducing signed message workflows used by APIs and webhooks.
Message and key input workflow. Lets you control the exact message and secret used in the generated signature during debugging.
Recent HMAC history. Stores a short local history of generated values for faster comparison in repeated test sessions.
Copy-ready output. Move the generated signature directly into your verification, testing, or documentation workflow.

Common use cases.

Verifying a webhook signature. Developers can reproduce the expected signature and compare it with what the provider sent.
Testing API request signing. Teams can verify whether their secret key and algorithm configuration produce the required HMAC output.
Debugging integration mismatches. QA engineers can isolate whether an auth issue is caused by payload formatting, algorithm choice, or secret key usage.
Learning message authentication concepts. Students and junior developers can see how shared-secret signatures differ from plain hashes.

How to use it.

Enter the message — Provide the exact payload or text that should be signed.
Enter the secret key — Add the shared secret used to generate the HMAC signature.
Choose the algorithm — Select the HMAC variant required by your target system.
Generate the HMAC — Run the generator and produce the signature from the message and secret.
Compare or copy the result — Use the output in your verification flow, documentation, or debugging notes.

Examples

Webhook verification sample

Input: Message: order=123 | Secret: webhook_secret | Algorithm: SHA-256

Output: A hex-encoded HMAC signature that can be compared with a provider header value.

Signed API request

Input: Message: GET:/v1/balance:1700000000 | Secret: api_shared_key

Output: A deterministic HMAC digest used to validate the request on the receiving side.

Algorithm comparison

Input: Same message and key with SHA-256 vs SHA-512

Output: Different valid HMAC outputs that illustrate how algorithm choice affects the signature.

Troubleshooting

My HMAC does not match the provider signature

Cause: The message body, secret key, algorithm, or formatting may differ from what the provider signed.

Fix: Verify the exact raw payload, encoding, key value, and algorithm requirement before comparing outputs again.

The same message generates different signatures elsewhere

Cause: Line endings, whitespace, character encoding, or message serialization may differ across systems.

Fix: Make sure both environments use the identical byte representation of the message before generating the HMAC.

I expected encryption instead of a signature

Cause: HMAC only authenticates and verifies integrity; it does not hide the underlying message.

Fix: Use encryption or transport security in addition to HMAC if the message contents must remain confidential.

FAQ · 05

What is the difference between HMAC and a normal hash?

A normal hash depends only on the input message, while an HMAC depends on both the message and a secret key. That makes HMAC useful for message authenticity and integrity verification because only parties with the shared secret can reproduce the same signature reliably.

When is HMAC commonly used?

HMAC is commonly used in API authentication, webhook verification, signed callbacks, shared-secret request validation, and systems where two parties need to verify message integrity without exposing the secret directly. It is especially common in payment and infrastructure integrations.

Which HMAC algorithm should I choose?

Use the algorithm required by the system you are integrating with. SHA-256 is a common modern default, while some providers use SHA-1 for compatibility or SHA-512 for stronger output. The right choice is usually determined by the receiving service's documentation.

Does HMAC encrypt the message?

No. HMAC does not encrypt or hide the message contents. It only produces a signature used to verify integrity and shared-secret knowledge. If confidentiality is required, you still need transport security or encryption in addition to HMAC.

Why would two HMAC values differ for the same message?

Differences usually come from a changed secret key, altered whitespace or formatting in the message, encoding mismatches, or use of a different algorithm. Even small message changes can produce a totally different HMAC output.

Developer Note

Furkan Beydemir — Frontend Developer

HMAC bugs are often tiny formatting bugs that take too long to spot. I built this generator so developers can reproduce signatures quickly and focus on the real integration mismatch.

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