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Guide

How to use this tool, examples, and related tips.

How to Use the HMAC-SHA256 Generator

Enter your message in the message field.

Enter your secret key.

The HMAC-SHA256 tag is computed instantly and displayed as a 64-character hexadecimal string.

Copy the output for use in your API request, webhook verification, or JWT signing workflow.

What Is HMAC-SHA256?

HMAC-SHA256 is the HMAC construction applied using SHA-256 as the underlying hash function. It produces a 256-bit (64-character hex) authentication tag and is the most widely deployed HMAC variant in production systems today. HMAC-SHA256 is used to sign API requests (AWS Signature Version 4, Stripe, Shopify, and many others), verify webhook payloads (GitHub, Stripe, Twilio), construct JWT signatures (HS256), and authenticate messages in TLS and IPsec. It provides strong authentication with no known practical vulnerabilities and is supported natively in virtually every programming language and cryptographic library.

When to Use This Tool

API request signing — Reproduce the HMAC-SHA256 signature for an API request manually to debug authentication failures or verify your signing implementation.

Webhook signature verification — Compute the expected HMAC-SHA256 of a webhook payload and compare it against the signature header to confirm authenticity.

JWT HS256 debugging — JWT tokens signed with HS256 use HMAC-SHA256. Manually compute the signature component to verify or debug JWT signing behavior.

AWS Signature Version 4 — AWS uses a chained HMAC-SHA256 construction to sign API requests. Use this tool to reproduce individual HMAC steps during debugging.

Related Tools

  • HMAC generator
  • HMAC-SHA512 generator
  • SHA-256 hash generator
  • JWT decoder
  • Bcrypt generator

FAQ

Answers about this tool and how your data is handled.

Why is HMAC-SHA256 preferred over other HMAC variants?

HMAC-SHA256 combines SHA-256's strong security properties with broad library support, well-documented specifications, and wide adoption in industry-standard protocols. It is the default choice in most modern API authentication and webhook signing schemes.

What encoding should my key and message use?

By default, treat both as UTF-8 strings. Some APIs require keys or messages in specific encodings (hex, Base64) — check the API documentation and pre-process accordingly before using this tool.

Does HMAC-SHA256 encrypt my message?

No. HMAC-SHA256 produces an authentication tag — it proves the message came from someone holding the secret key and has not been tampered with. The message content remains in plaintext.

Does this tool send my data to a server?

No. HMAC computation runs entirely in your browser. Your message and secret key never leave your machine.

What is the output length of HMAC-SHA256?

Always 64 hexadecimal characters, representing 256 bits.

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