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JWT decoder in Visual Studio

So far I always used JWT.io to decode my JWT tokens. But today I discovered that I don't have to leave my Visual Studio IDE anymore. But before I show you this feature, let’s just briefly summarize what JWT tokens are.

JWT what?

JWT (JSON Web Token) is a compact, URL-safe token format used for securely transmitting information between parties. It is commonly used in authentication and authorization scenarios, especially in web and mobile applications.

A JWT consists of three parts:

  1. Header: Contains metadata about the token, such as the signing algorithm used (e.g., HS256 or RS256).
  2. Payload: Contains the claims, which are statements about the user or other data (e.g., user ID, roles). This data is not encrypted, so it should not include sensitive information.
  3. Signature: A cryptographic signature that ensures the token has not been tampered with. It is created by encoding the header and payload, then signing them using a secret key or public/private key pair.

JWT tokens are typically used in stateless authentication, meaning that once issued, the server doesn't need to store session data. The client sends the JWT with each request (usually in the Authorization header), and the server can validate it to authenticate the user.

The payload in a JWT is typically Base64Url encoded. This encoding is a variant of Base64, designed to be URL-safe. Unlike regular Base64, Base64Url replaces characters that might cause issues in URLs:

  • + is replaced with -
  • / is replaced with _
  • The padding = is removed

This allows the JWT to be safely transmitted in URLs, headers, or query parameters without needing further encoding. So to read the payload during debugging I typically used JWT.io before.

Decoding JWT tokens in Visual Studio

Today when reading a JWT formatted access token in Visual Studio, I noticed that a debugger visualizer was available that decoded it for me:

 


There was nothing extra that needs to be done as Visual Studio recognized the string as a JWT token automatically and selects the correct debugger visualizer for you.

Nice!

More information

JWT.io: Decode, verify and generate JSON Web Tokens (bartwullems.blogspot.com)
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