SAML Message Decoder is a free Chrome add-on developed by Magnus Suther. It falls under the category of browsers and specifically, the subcategory of add-ons and tools. This tool is designed to help users debug their SAML based SSO/SLO implementations.

The SAML Message Decoder runs in the background, collecting SAML messages as they are sent and received by the browser. When something doesn't work as expected, users can simply pop up the extension to view the latest SAML messages in cleartext, which are easily readable XML. This allows users to understand what happened and provides insights on how to solve authorization issues.

The add-on also comes with several updates, including support for EidSignRequest and EidSignResponse messages, removal of fullpage.js for faster loading, adjustments for a better appearance in the Firefox popup, and fixes for parsing and recording large SAML messages. Additionally, it offers functionality to copy one or more SAML messages to the clipboard and supports exporting messages to a .json file, making it convenient for analysis even when users don't have direct access to the client's computer.

Overall, SAML Message Decoder is a valuable tool for developers and system administrators working with SAML based SSO/SLO implementations, providing a clear and accessible way to debug and analyze SAML messages.