JWT Decoder

The JWT Decoder takes a JSON Web Token — the compact, three-part, dot-separated string used everywhere in modern authentication — and splits it into its readable header, payload, and signature sections so you can inspect exactly what claims and metadata it carries. Paste a token and the tool immediately shows you the decoded JSON of the header (typically the signing algorithm and token type) and the payload (the actual claims, such as user ID, issued-at time, expiry, and any custom application data), all formatted and pretty-printed for easy reading. Backend developers, frontend engineers integrating with an auth provider, and QA engineers debugging a failed login flow use this tool constantly. When a session mysteriously expires early, or an API call is rejected with an "invalid token" error, decoding the JWT is often the fastest way to see what's actually inside it — you can check the "exp" (expiration) claim to confirm the token's lifetime, check "iat" (issued at) to see when it was minted, and inspect custom claims like roles or tenant IDs to confirm your authorization logic is receiving what it expects. It's also invaluable when working with third-party OAuth or SSO providers, since you can paste an access token or ID token straight from a browser's network tab and immediately see its structure without writing a line of code. It's critical to understand what this tool does not do: it decodes and displays the token's contents, but it does not verify the cryptographic signature. Because JWTs use Base64URL encoding rather than encryption for the header and payload, anyone who has the token string can read its contents — a JWT is not a secure way to hide information, only a tamper-evident way to transmit claims when the signature is properly verified server-side. Never assume a decoded payload is trustworthy just because you can read it; genuine verification requires checking the signature against the issuer's public key or shared secret, which should always happen on your server, not in a client-side viewer like this one. This distinction matters especially when debugging security issues: if you're trying to determine whether a token is legitimately signed, you need your backend's verification library, not a decoder. But for the very common task of "what does this token actually say," decoding is exactly the right tool, and it saves you from manually splitting the string on periods and running each segment through a Base64 decoder yourself. Pair this tool with the Base64 Encoder/Decoder for related encoding tasks, and the JSON Formatter for further inspecting complex nested claims. Everything is decoded entirely client-side in your browser — your token, which may carry sensitive session or user data, is never sent to a server or logged anywhere, making this safe to use even with production tokens during live incident debugging.