What is JWT? How to Decode and Inspect JWT Tokens

What is JWT?

A JSON Web Token (JWT) is a compact, self-contained way to securely transmit information between parties as a JSON object. This information can be verified and trusted because it is digitally signed.

JWTs are commonly used for:

• Authentication – After login, each request includes the JWT to verify the user
• Information Exchange – Securely transmit data between parties

JWT Structure

A JWT consists of three parts separated by dots: Header.Payload.Signature

1. Header

The header typically contains the token type (JWT) and the signing algorithm (e.g., HS256).

2. Payload

The payload contains the claims — statements about an entity (user) and additional data.

3. Signature

The signature is used to verify the token hasn't been tampered with.

Common JWT Claims

• iss – Issuer
• sub – Subject (user ID)
• aud – Audience
• exp – Expiration time
• iat – Issued at
• jti – JWT ID

Security Tips

1. Never put sensitive data in JWT payload — it can be decoded by anyone
2. Always verify the signature server-side
3. Set appropriate expiration times
4. Use HTTPS to prevent token interception
5. Rotate secrets regularly

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Use our JWT Decoder to decode any JWT token instantly in your browser.