JWT Decoder
Decode JSON Web Tokens (JWT) securely in your browser. No data is sent to the server.
About the JWT Decoder
Most JWT decoders online — including the famous one — POST your token to a server before decoding it. That's a problem when the token belongs to a real user session, a production API, or a customer support escalation. This decoder splits the token client-side and base64url-decodes each part inside your browser, so the raw token bytes never touch the network. Header algorithm, payload claims (with iat / exp formatted as human-readable dates), and the raw signature are displayed side by side. Signature verification is intentionally left to your backend — this tool is for inspection, not validation.
Common use cases
- Inspect a production access token without leaking it
- Check the exp claim to debug expired-session issues
- Verify which scopes / roles are present in a customer's token
- Debug Auth0 / Cognito / Clerk / Supabase token contents
- Confirm the alg header matches what your verifier expects
Why client-side?
Every byte you paste, type, or upload here is processed entirely inside your browser. Nothing is sent to a server, logged, or stored. That means it's safe to use this tool on production secrets, customer data, internal logs, and any input you would not paste into a hosted SaaS formatter.
Related tools
- Base64 Encoder/Decoder Encode and decode Base64 strings in your browser. Handles UTF-8, emoji, and binary safely via TextEncoder. Use for data URIs, JWT inspection, and Basic Auth headers.
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- Private JSON Formatter & Validator - Fast, Client-Side Data Tool Free JSON formatter and validator that runs entirely in your browser. Beautify, validate, and pretty-print JSON with no uploads, no sign-up, and no data leaving your device.
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Frequently Asked Questions
- How do I decode a JWT token?
- Paste your JWT string into the input field. The tool instantly decodes and displays the header, payload, and signature sections.
- Is it safe to decode JWTs in a browser?
- Yes. This tool runs entirely in your browser. Your JWT is never sent to any server, keeping your tokens secure.
- What information is stored in a JWT?
- A JWT contains three parts: a header (algorithm and type), a payload (claims like user ID and expiration), and a signature for verification.