Security Tools
JWT Decoder
Instantly decode a JWT's header and payload, right in your browser.
Paste your JWT below to instantly decode its header and payload - entirely in your browser, your token is never sent to our servers.
Decoding happens entirely in your browser - your token is never sent to our servers.
JustChecker builds tools that respect your data - this one never leaves your browser.
Frequently Asked Questions
No - decoding happens entirely in your browser using JavaScript. Your token, including any sensitive claims it contains, is never transmitted anywhere.
No - it only decodes the header and payload, which are Base64URL-encoded but not encrypted or protected. Verifying a signature requires the issuer's secret or public key, which only your backend should have.
No - anyone can craft a JWT with arbitrary header/payload content. Only a signature verification (done server-side, with the correct secret/key) proves a token is genuine and untampered.
A JWT has a header (algorithm and token type), a payload (the claims/data), and a signature (used to verify authenticity) - each separated by a period and independently Base64URL-encoded.