git mergetool

Hands conflicts to vimdiff/meld/kdiff3/etc.

🎯 What & why

git mergetool shells out to an external 3-way merge tool for every unmerged path. When the conflict markers in your editor turn into a wall of <<<<<<<, this is the escape hatch.

🧠 Mental model

It's a driver, not a merger. Git already produced LOCAL, REMOTE, and BASE; mergetool just hands those three files to vimdiff/meld/kdiff3 and writes whatever you save back into the working tree.

🛠️ Synopsis

git mergetool [--tool=<tool>] [--tool-help] [-y|--no-prompt|--prompt]
              [-O<orderfile>] [--[no-]gui] [<file>...]

🎚️ Switches & options

Flag	What it does
`--tool=<tool>`	Pick a tool: `vimdiff`, `meld`, `kdiff3`, `bc`, `opendiff`, ...
`--tool-help`	List the merge tools Git knows how to drive on this box.
`-y, --no-prompt`	Skip the Hit return to start merge resolution tool prompt. Use this if you trust the tool.
`-O <orderfile>`	Process conflicts in the order listed in `<orderfile>`. Handy for huge merges.
`--gui / --no-gui`	Honor `merge.guitool` instead of `merge.tool`. Or don't.
`--prompt`	⚠️ The default. Annoying when scripted; explicit when interactive.

💡 Use cases

Conflict hunks are too tangled to eyeball — you want a real 3-pane diff.
Binary-ish files (XML, generated code) where text markers are useless.
You configured a team-standard tool and want everyone resolving the same way.
Resuming a merge after a break — mergetool enumerates remaining conflicts.

🧪 Examples

List drivers Git ships with

git mergetool --tool-help

Resolve with meld, no prompts

git mergetool --tool=meld -y

Set a default and forget it

git config --global merge.tool kdiff3
git config --global mergetool.keepBackup false
git mergetool

Resolve only one path

git mergetool src/parser.c

🎓 Recommendations

Set mergetool.keepBackup = false once you trust your tool — those *.orig files breed in your working tree.
Pick a tool you actually know. vimdiff is powerful; meld is friendlier. Don't audition during a fire.
Configure merge.conflictStyle = zdiff3 — even with mergetool, the in-file markers improve when you peek.

🪤 Common pitfalls

Forgetting mergetool.keepBackup=false leaves .orig files everywhere. Add them to .gitignore or clean up.
Saving with no changes still counts as resolved. Closing without saving leaves the conflict — Git asks if it was successful.
Custom mergetool.<tool>.cmd strings need correct quoting of $LOCAL/$REMOTE/$BASE/$MERGED. Get it wrong and you'll silently lose work.

🔗 Related modules

📝 Quiz

Hit each option, then Check answers. Score is recorded; Next is always open.