You can configure Fossil’s gdiff command to launch your favorite graphical diff tool. Below are examples configuring some popular diff tools.

All the examples below include the --global option. If you want to configure this setting only for the current repository, omit that option.

Beyond Compare:

$ fossil settings --global gdiff 'bcomp'

Git:

$ fossil settings --global gdiff 'code --diff --wait'

vimdiff:

$ fossil settings --global gdiff 'vimdiff'

Visual Studio Code:

$ fossil settings --global gdiff 'code --diff --wait'