Encoding

JWT Decoder

Decode a JSON Web Token's header and payload in your browser. Tokens are never uploaded.

NewBrowser-only

Focused calculator

Calculate JWT Decoder

{
  "header": {
    "alg": "HS256",
    "typ": "JWT"
  },
  "payload": {
    "sub": "1234",
    "name": "Jane Doe",
    "iat": 1516239022
  }
}

Decoded header and payload

Guide & details

When to use this tool

Use the JWT Decoder for quick, focused data cleanup directly on the page before copying the output into code, documentation, spreadsheets or another tool.

Developer, SEO, analytics and content workflows where text needs to be encoded, decoded or normalized safely.
Cleaning a value before pasting it into a URL, HTML page, config file or API request.
Checking privacy notes before using sensitive text such as tokens or copied session data.

Accuracy, privacy and assumptions

This is a browser-only tool: input is processed by JavaScript on the page and is not uploaded to Convematik.
For copied tokens, session data or private payloads, still review the output carefully before sharing it anywhere else.

Common mistakes to avoid

Most wrong answers from a JWT Decoder come from unit direction, rounding too early, or copying a result without its original context.

Do not assume encoding encrypts data. Base64, URL encoding and HTML entities are reversible representations.
Decode untrusted strings carefully because the output can contain scripts, markup or control characters.
For private tokens or session strings, prefer browser-only tools and avoid unnecessary sharing.
Do not paste the generated output into another service until you have removed anything private or account-specific.

Copy-ready result format

JWT Decoder output: { (Decoded header and payload).

Keep the original input available until the destination accepts the transformed output.
Copy validation errors along with the input when debugging a failed import.
Use browser-only pages for sensitive copied text or account-like payloads.

Best workflow for JWT Decoder

Paste or type the input into the tool above.
Choose the target mode or format when the tool offers one.
Review validation errors and copy the output only after it matches the expected structure.
For sensitive data, prefer browser-only tools and avoid API-enabled endpoints.

Next steps after this result

After the immediate calculation, choose the next tool based on what you plan to do with the value.

Copy the transformed output into the destination and test it there.
Keep a copy of the original input.
Use browser-only pages for sensitive values.

Base64 Encode / Decode URL Encode / Decode Full unit converter Batch converter API docs

Formula

How it works: A JWT is three Base64URL segments joined by dots: header.payload.signature. The decoder Base64URL-decodes the first two segments and parses them as JSON. The signature is not verified.

Common examples

Input	Result
alg	HS256
typ	JWT
sub	1234

JSON API example

This tool runs entirely in your browser. Your input is never sent to a server, so there is no API endpoint for it.

Common questions

What does the JWT Decoder do?

Decode a JSON Web Token's header and payload in your browser. Tokens are never uploaded.

Does the JWT Decoder send my data to a server?

Everything in the JWT Decoder runs locally in your browser using JavaScript. Your input is never uploaded, logged or stored on a server.

When should I use the JWT Decoder instead of a spreadsheet or script?

Use the JWT Decoder for quick validation, formatting, decoding or cleanup when you need a deterministic output before copying the result into code, docs, an API request or a spreadsheet.

Is the JWT Decoder free to use?

Yes. The JWT Decoder is free and does not require an account.