JWT Decoder

About JWT Decoder

A JWT looks like an opaque string of characters, but it's actually just base64url-encoded JSON in disguise — readable by anyone the moment they know how to decode it, which is exactly what makes debugging authentication issues so much faster once you can see what's actually inside a given token. The JWT Decoder splits a token into its header and payload, decodes both back to readable JSON, and flags whether the token has already expired based on its `exp` claim — all without ever touching the signature, which requires a secret key this browser-based tool never has and has no business asking for. It's a routine debugging tool for developers working with authentication — checking what claims a token actually carries, confirming an expiration time matches what's expected, or verifying a backend is issuing tokens with the right shape. It's worth remembering this only decodes, never verifies: a token's contents are visible to anyone holding it whether or not its signature is actually valid, so never rely on a JWT's payload alone as proof of anything without server-side signature verification too.