Calculator
What the JWT Decoder does
JWT Decoder: transforms Status and Decoded JWT from JWT token. Example: the sample loaded on the page gives status Decoded (signature not verified).
Point it at JWT token and it returns Status and Decoded JWT. You can nudge a single number and watch the effect straight away.
Most people who open the JWT Decoder are people inspecting an API response. Most of these tasks are one-liners in a terminal, but not when you are away from one.
The work is done by JavaScript already loaded in your browser, so your input never crosses the network.
The sections that follow cover the fields, the method, and one full example computed from the defaults.
What do the JWT Decoder fields mean?
The JWT Decoder uses 1 input. Pre-filled inputs double as documentation: each one shows what a reasonable value looks like.
| Field | What to enter | Default |
|---|---|---|
| JWT token | paste or type any amount of text | eyJhbGciOiJub25lIn0.eyJzdWIiOiIxMjM0IiwibmFtZSI6IlRlc3QifQ. |
How does the JWT Decoder work?
Each output is derived from the inputs above in a single pass; there is no hidden state carried between runs, so the same inputs always give the same transformation.
Validation is deliberately strict: silently coercing a bad value is how wrong numbers get trusted.
Worked example
These are the values the JWT Decoder loads by default, and the result it produces from them. This is the worked example the page starts from, reproduced here so you can check the arithmetic.
| JWT token | eyJhbGciOiJub25lIn0.eyJzdWIiOiIxMjM0IiwibmFtZSI6IlRlc3QifQ. |
|---|
| Status | Decoded (signature not verified) |
|---|---|
| Decoded JWT | Header: { "alg": "none" } Payload: { "sub": "1234", "name": "Test" } |
How to use it
- Paste your content into JWT token.
- Each keystroke triggers a fresh calculation, which is cheap because it happens locally.
- You get Status and Decoded JWT back.
- Copy Link puts the current inputs in the URL, so bookmarking it brings the same numbers back.
What this tool does not do
- Output follows the common convention for this format; a specific toolchain may have its own house style.
- Processing happens in your browser, so extremely large inputs are bounded by available memory.
- It applies one method. If your situation calls for a different convention, the answer will not match.
Frequently asked questions
Only JWT token. Every box already holds a working value, which means a single edit is enough to get a meaningful answer.
With the values loaded when the page opens, status comes out as Decoded (signature not verified). The figure is derived from the inputs above, so it updates whenever they do.
No. The parsing happens in your browser, so sensitive payloads never leave your machine.
No. There is no account, no usage cap and no trial period. The site is funded by advertising rather than by charging for the tools.
It matches what you would get working it out by hand, with fewer opportunities to slip.