Understanding JSON Web Tokens (JWT) and How to Decode Them
An introduction to the structure of JWTs, how they secure modern APIs, and why decoding them client-side is crucial for debugging.
What is a JWT?
JSON Web Tokens (JWT) are the industry standard for securing API requests. When you log into a modern web application, the server responds with a JWT, which your browser stores and sends back with every subsequent request to prove you are authenticated.
The Three Parts of a JWT
A JWT looks like a long string of gibberish, but it actually consists of three distinct parts separated by periods (.):
exp).Why Decode JWTs?
When building frontend applications, developers often need to decode JWTs to check when a session expires or to read the user's role without making a database query. Because the Header and Payload are simply Base64Url encoded, they can be easily read.
Warning: You should never paste production JWTs into random online decoders that might log your tokens on their servers. Use our [JWT Decoder](/tools/jwt-decoder) which processes your tokens 100% locally in your browser.
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