ToolSnippet
🔐Part of Security, Hashing & Crypto

Online JWT Builder, Signer & Verifier

Construct custom JSON Web Tokens (JWT), configure standard registered claims (exp, iat, sub, iss), sign tokens using HMAC-SHA256/384/512, and verify signatures with zero server exposure.

About This Tool

ToolSnippet's JWT Builder is a cryptographic utility for backend and full-stack developers. It allows you to generate signed JWTs for testing API authentication, debugging microservices, and validating auth tokens with client-side Web Crypto APIs.

Key Features

HMAC signing with HS256, HS384, and HS512
Custom payload claims editor with JSON validation
1-click Epoch expiration calculator (+15m to +30 days)
Secure random secret key generator
Interactive signature verification tester
1-click copy for signed tokens

How to Use

  1. 1Choose your signing algorithm (HS256, HS384, HS512, or none).
  2. 2Edit your Header and Payload JSON claims in the workstation.
  3. 3Use the quick expiration helpers (+15m, +1 hour, +24h, +7 days) to set the 'exp' claim timestamp.
  4. 4Enter your secret key (or generate a secure random secret).
  5. 5View your generated 3-part signed JWT (Header.Payload.Signature) in real-time.
  6. 6Copy the token or test signature verification with 1-click.

Why Use ToolSnippet JWT Builder & Signer?

Zero Server Transmission: Cryptographic HMAC signing executes locally in browser RAM using the native Web Crypto API.
Quick Time Claim Calculators: Easily inject accurate UNIX epoch timestamps for 'iat', 'nbf', and 'exp'.
Visual Color-Coded Breakdown: Instantly distinguish Base64URL header, payload, and cryptographic signature segments.

Tips for Best Results

  • Always use strong, high-entropy secret keys (at least 256 bits) for HS256 tokens in production.
  • Verify that the 'exp' claim is set in UNIX epoch seconds, not milliseconds.

Frequently Asked Questions

Is my secret key safe when signing JWTs here?

Yes, 100%. All cryptographic hashing and HMAC signature generation are executed locally via window.crypto.subtle. No secrets or tokens are ever sent across the network.

What is the structure of a signed JWT?

A JWT consists of three Base64URL-encoded parts separated by dots: 1. Header (algorithm and token type), 2. Payload (claims and data), 3. Signature (HMAC or digital signature ensuring data integrity).

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