Can DevToolery verify the signature?

No. Verification needs the signing key, and a tool that asks you to paste your signing secret into a web page is a tool worth distrusting. Verify server-side with your own library.

Is my token stored anywhere?

No. It stays in a React state variable for the life of the tab. Snippet saving is disabled on this tool and input persistence never applies to it.

JWT Decoder

Read the header and payload of a token. Decoding is not verification.

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About this tool

Splits the token on dots and Base64url-decodes the first two segments. Registered claims are pulled out and rendered as readable dates. The signature is shown as an opaque string and is not checked.

Limitations

The signature is not verified. A decoded token tells you what it claims, not whether the claim is true.
Tokens are never written to storage, the URL, or the page title.

Questions

Can DevToolery verify the signature?: No. Verification needs the signing key, and a tool that asks you to paste your signing secret into a web page is a tool worth distrusting. Verify server-side with your own library.
Is my token stored anywhere?: No. It stays in a React state variable for the life of the tab. Snippet saving is disabled on this tool and input persistence never applies to it.

Privacy

This page does its work in your browser. What you paste is processed by JavaScript running on your own device and is never sent to a DevToolery server — there is no server that could receive it. The page itself is a static file delivered by a CDN. See exactly what is stored.