Mercurial has the ability to add new features through the use of extensions. Extensions may add new commands, add options to existing commands, change the default behavior of commands, or implement hooks. To enable the "foo" extension, either shipped with Mercurial or in the Python search path, create an entry for it in your configuration file, like this:: [extensions] foo = You may also specify the full path to an extension:: [extensions] myfeature = ~/.hgext/myfeature.py See :hg:`help config` for more information on configuration files. Extensions are not loaded by default for a variety of reasons: they can increase startup overhead; they may be meant for advanced usage only; they may provide potentially dangerous abilities (such as letting you destroy or modify history); they might not be ready for prime time; or they may alter some usual behaviors of stock Mercurial. It is thus up to the user to activate extensions as needed. To explicitly disable an extension enabled in a configuration file of broader scope, prepend its path with !:: [extensions] # disabling extension bar residing in /path/to/extension/bar.py bar = !/path/to/extension/bar.py # ditto, but no path was supplied for extension baz baz = !