JWT Decoder
About JWT Decoder
JSON Web Tokens (JWTs) have become the de facto standard for authentication and authorization in modern web applications. A JWT consists of three Base64-encoded parts separated by dots: a header containing the algorithm and token type, a payload containing claims and user data, and a cryptographic signature that ensures the token has not been tampered with.
This free JWT decoder tool allows you to quickly inspect the contents of any JWT without needing to write code or use command-line tools. Simply paste your token and instantly see the decoded header and payload with syntax highlighting. The tool automatically detects timestamp fields like iat (issued at), exp (expiration), and nbf (not before), converting them to human-readable dates for easy interpretation.
Important: This tool only decodes JWTs; it does not verify signatures. JWT payloads are merely Base64-encoded, not encrypted, meaning anyone with access to a token can read its contents. The signature verification step, which confirms the token was issued by a trusted source and has not been modified, requires access to the secret key (for HMAC algorithms) or public key (for RSA or ECDSA algorithms) and must be performed server-side.
All processing happens entirely in your browser using JavaScript. Your tokens are never sent to any server, making this tool safe to use with production tokens. You can use it for debugging authentication issues, inspecting token claims, checking expiration times, or simply learning how JWTs are structured.