JWT Encoder/Decoder

Inspect the contents of a JSON Web Token by decoding its three dot-separated parts. The header and payload are parsed from base64url into formatted JSON, and the signature segment is shown verbatim. Decoding is purely local — the token never leaves your browser, and no signing or verification is performed.

1. Paste the JWT (typically starting with eyJ) into the input field.\n2. Click Decode.\n3. Read the Header (red), Payload (purple), and Signature (blue) cards, each with a Copy button.\n4. Use Clear to reset. A toast confirms a successful decode or reports a parse error.

A JWT must contain exactly three dot-separated segments. The tool first checks the segment count, then decodes header and payload by mapping base64url -/_ to +//, adding = padding, and running atob, finally parsing the result as JSON. The signature is displayed as-is without verification. Errors are surfaced for wrong segment counts, malformed header JSON, or malformed payload JSON. Common payload claims like exp, iat, and sub appear as ordinary JSON fields and are not specially interpreted.