What does "signatures are not verified" mean in practice?

Verifying needs the signing key and the algorithm, and a key in the browser is no longer a secret. So this tool only decodes: anyone holding the token can read exactly the same content. Verify signatures on the server, with the same key that signed them.

The output is garbled, or it says Invalid JWT — why?

The three-part error means it is not a JWT (a missing signature segment, for example). Garbled output usually means the segment is not standard base64url; this tool already accepts base64url without padding, so the next thing to check is whether the token was truncated when copied.

JWT Decoder

Decode a JWT to inspect its header and payload claims.

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Processed locally

JWTs are only Base64-decoded here — signatures are not verified. Do not rely on decoded sensitive data in production.

Enter a JWT

Enter a JWT to see its decoded contents

About JWT decoding

JSON Web Token (JWT) is an open standard (RFC 7519) for transmitting information between parties securely.

Header: token type and signing algorithm
Payload: the claims, carrying user information and more
Signature: verifies the token's integrity

About JWT Decoder

Decodes a JWT header and payload and shows the expiry — locally, so the token is never sent anywhere.

1
Decodes both segments as base64url, padding or not, and reads the payload as UTF-8 — accented and CJK claims come out as text, not mojibake.
2
A token with an exp claim also gets a readable expiry and an expired flag, evaluated against your own clock.
3
Parsing happens entirely in the browser, so the token is never uploaded — which is also why the page states plainly that it does not verify the signature.

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