JWT Decoder

Decode JWT tokens into header, payload, and signature.

freeworks offlinenothing uploaded
Input
Output
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About jwt decoder

JWT Decoder does its work in front of you rather than sending anything away to be processed. What you see is the whole of it.

Your input goes into a function and the result comes back out, both inside this tab. There is no round trip and no third party in the middle.

You will find it under Tokens, alongside 9 other tools for the same sort of job.

Parses base64url-encoded header and payload claims, displays the raw signature. Note: signatures are NOT verified, use the JWT Debugger to check expiry and algorithm.

How to use it

01
Start it
Every control is on the tool itself. Keyboard shortcuts, where there are any, are listed beside it.
02
Watch it run
It updates in the page as you go. Nothing is sent anywhere, so it keeps working with the network off.
03
Close when done
Nothing is stored between visits. Reloading gives you a clean start rather than picking up where you left off.

Examples

Decode HS256 JWT with user claims
Decode a JWT signed with HS256 to inspect its header, payload, and signature
Input
eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJzdWIiOiIxMjM0NTY3ODkwIiwibmFtZSI6IkpvaG4gRG9lIiwiaWF0IjoxNTE2MjM5MDIyfQ.SflKxwRJSMeKKF2QT4fwpMeJf36POk6yJV_adQssw5c
Output
Signature: SflKxwRJSMeKKF2QT4fwpMeJf36POk6yJV_adQssw5c

HEADER
Alg: HS256
Typ: JWT

PAYLOAD
Sub: 1234567890
Name: John Doe
Iat: 1516239022

Questions

Does JWT Decoder work offline?+

Yes. It is JavaScript running in this tab, so once the page has loaded it needs nothing further from the network. Put the machine in flight mode and it carries on. Nothing you do here is sent anywhere, because there is nowhere for it to go.

Does it remember anything between visits?+

No. Reload the page and it starts from nothing. There is no account, no saved state and no cookie holding your last session. That is a deliberate trade: it cannot lose your data because it never keeps any.

Is it accurate?+

Timing comes from performance.now(), the high resolution clock the browser provides, rather than from setInterval, which drifts by a few milliseconds every tick and compounds over minutes. What can still shift things is the browser throttling a tab in the background, so leave it visible if the timing matters.

Does it make a sound?+

Where a sound makes sense, it is generated with the Web Audio API rather than loaded as a file, so there is nothing to download and nothing to block. Browsers refuse to start audio until you have interacted with the page, which is why the first press is what switches it on.

Can I use JWT Decoder on a phone?+

Yes. The controls are sized for touch and the layout collapses to one column on a narrow screen. Bear in mind that a phone locking its screen will suspend the page, and timing stops with it.