JWT Decoder – Free Online JSON Web Token Decoder

A JWT decoder is a tool that reads a JSON Web Token and displays its contents in plain readable JSON. A JWT has three parts separated by dots: the header, the payload, and the signature. The header describes the algorithm used to sign the token. The payload contains the actual claims like user ID, expiry time, and issuer. Decoding simply means reading these parts, which are Base64 encoded, not encrypted.

Yes. Decoding a JWT does not require a secret key because the token is encoded not encrypted. Anyone with the token can read the header and payload by Base64 decoding them. The secret key is only needed to verify the signature, which proves the token was issued by a trusted source and has not been tampered with. This tool decodes but does not verify.

After decoding you can see everything in the header and payload. The header typically shows the token type and signing algorithm such as HS256 or RS256. The payload shows claims like sub which is the subject or user identifier, iss which is the issuer, exp which is the expiry timestamp, and iat which is the time the token was issued. Applications can also add custom claims for their own purposes.

It is safe when the tool runs entirely in your browser without sending data to a server. This tool processes everything locally using JavaScript. Your token never leaves your machine. That said avoid pasting tokens that are still active and grant access to sensitive production systems in any public tool as a general security practice.

You can decode a JWT in JavaScript by splitting the token on the dot character, taking the second part which is the payload, and passing it to atob() to Base64 decode it, then parsing the result with JSON.parse(). For production use the jsonwebtoken library on Node.js handles both decoding and verification and is the industry standard.

A JWT consists of three Base64 encoded sections separated by dots. The first is the header which contains the token type and algorithm. The second is the payload which contains the claims or data. The third is the signature which is created by signing the header and payload with a secret key. The signature cannot be decoded, only verified using the original key.