How do I decode a JWT token?

Paste your token into the decoder above. The header, payload, and signature are separated and displayed as JSON. No secret key is needed to view the contents.

Can I decode a JWT without the secret key?

Yes. JWT contents (header and payload) are Base64URL-encoded, not encrypted. You can always decode and read them. The secret key is only needed to verify the signature.

What is the difference between HS256 and RS256?

HS256 uses a shared secret (symmetric) for both signing and verification. RS256 uses a private key to sign and a public key to verify (asymmetric). RS256 is preferred when the verifier shouldn't have signing access.

Is it safe to decode JWT tokens online?

This tool runs entirely in your browser. Your tokens are never sent to any server. All decoding, verification, and generation happens client-side using JavaScript.

JWT Decoder & Generator | Kopdog Dev Tools

Decode

Generate

JWT Token

Verification Key/Secret Optional - leave empty for decode only

Secret is Base64 encoded

Header

Payload

Signature

About JSON Web Tokens (JWT)

JSON Web Tokens (JWT), defined in RFC 7519, are compact, URL-safe tokens used to securely transmit claims between two parties. They are widely used for authentication and authorization in web applications and APIs.

JWT Structure

A JWT consists of three Base64URL-encoded parts separated by dots: header.payload.signature

Header - declares the token type (JWT) and the signing algorithm (e.g. HS256, RS256).
Payload - contains the claims (data), such as user identity and expiration time.
Signature - verifies the token hasn't been tampered with, created by signing the header and payload with a secret or private key.

Common JWT Claims

Claim	Name	Description
`sub`	Subject	Identifies the principal (usually a user ID)
`iss`	Issuer	Who issued the token
`aud`	Audience	Intended recipient(s) of the token
`exp`	Expiration	Unix timestamp after which the token is invalid
`iat`	Issued At	Unix timestamp when the token was created
`nbf`	Not Before	Unix timestamp before which the token is not valid
`jti`	JWT ID	Unique identifier to prevent token reuse

Signing Algorithms Compared

Algorithm	Type	Best For
`HS256`	Symmetric (HMAC-SHA256)	Simple setups where signer and verifier share a secret
`RS256`	Asymmetric (RSA-SHA256)	Distributed systems where verifiers shouldn't have signing access
`ES256`	Asymmetric (ECDSA-P256)	Like RS256 but with smaller keys and faster signing

Security Best Practices

Always verify the signature before trusting any claims in the payload.
Don't store sensitive data in the payload - JWTs are encoded, not encrypted. Anyone can read the contents.
Use short expiry times (exp) and refresh tokens for long-lived sessions.
Reject the "none" algorithm in your verification logic to prevent signature bypass attacks.
Validate the expected algorithm on the server side rather than trusting the token's header.