JWT Builder

Create JWT tokens with custom headers, payload claims, and a secret key. Uses HS256 signing via the browser's Web Crypto API. Color-coded output shows each token segment. Great for testing auth flows.

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Frequently Asked Questions

What is a JWT?▼

A JSON Web Token (JWT) is a compact, URL-safe token format for securely transmitting claims between parties. It consists of three Base64url-encoded parts: header (algorithm), payload (claims), and signature — joined by dots.

What does HS256 mean?▼

HS256 is HMAC with SHA-256 — a symmetric signing algorithm where the same secret key is used to both sign and verify the token. It's the most common JWT algorithm for server-to-server auth where both sides share the secret.

What are common JWT claims?▼

Standard claims include: sub (subject/user ID), iat (issued at, Unix timestamp), exp (expiration, Unix timestamp), iss (issuer), aud (audience), and nbf (not before). You can also add custom claims like name, email, or role.

Is it safe to use this tool with real secrets?▼

No — use this tool for learning and testing only. For production JWTs, generate tokens server-side where your secret key is never exposed to the browser or client.

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