The mergetool is a software that resolves a Git conflict.
You need to install a mergetool such as:
See git mergetool –tool-help for a full list
You can configure it
git config merge.tool tortoisemerge
git config merge.conflictstyle diff3
git config mergetool.prompt false
git config --global merge.tool meld
git config --global mergetool.meld.path "C:\Meld\Meld.exe"
git config --global merge.tool code
You can open it then with:
git mergetool
Example of output where mergetool is not configured but will still open tortoisemerge as I have it already installed on my computer thanks to TortoiseGit
This message is displayed because 'merge.tool' is not configured.
See 'git mergetool --tool-help' or 'git help config' for more details.
'git mergetool' will now attempt to use one of the following tools:
tortoisemerge emerge vimdiff
Merging:
syntax.php
Normal merge conflict for 'syntax.php':
{local}: modified file
{remote}: modified file
Hit return to start merge resolution tool (tortoisemerge):