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Castor is a lightweight but full-featured gemini server, focused on ease of setup and use.

Servers are configured using Castorfiles, analogous to Caddyfiles or nginx configurations. Various handlers can be defined:

  • static file serving
  • hard-coded responses

Castorfiles also support client cert requirements; lists of client certificate hashes can be provided for authentication, or simply as session-management (hashes being passed off to a backend server for mapping to a user identity).


Castor is the second-brightest object in the zodiac constellation of Gemini and one of the brightest stars in the night sky, as well as one of a pair of twin half-brothers, along with his brother Pollux.