JWT Decoder

The tool decodes a JWT string into its header and payload for analysis. It splits the token into three base64url-encoded segments, decodes them, and presents the header and payload as structured JSON. It can operate in decode-only mode or perform optional signature verification when a secret or public key and algorithm are provided. This enables local debugging without network calls or external services. The core value is for developers, QA, and security teams who need rapid insight into token contents and claim values without relying on server-side handlers. The tool adheres to standard JWT conventions, including registered claim names like exp, iat, and aud, and formats timestamps into human-readable forms. It handles common encoding quirks such as missing padding and invalid base64url chars, and reports precise decoding errors when segments fail. By keeping verification local, it reduces exposure and supports repeatable testing across Python-based pipelines. The approach emphasizes correctness, determinism, and minimal dependencies, making it suitable for CI scripts and local toolchains. Unique differentiators include strict base64url decoding, clear claim interpretation, and robust error reporting, plus optional verification with user-provided keys. Use cases include token inspection during API development, security reviews, and debugging authentication flows in microservices architectures.