mergetools

Mergetools are software tools designed to help resolve differences between file versions by presenting a coherent interface for performing merges, typically using a three-way merge that compares a base version with local and remote or updated variants. They are used when version control systems report conflicts during merges or pulls.

A mergetool analyzes three versions: the common ancestor, the local working copy, and the incoming changes, and attempts to combine changes. If changes touch the same region, it presents a conflict and requires user input. Most tools provide side-by-side views, syntax highlighting, inline editing, and conflict markers. They may support auto-merge heuristics, directory comparison, and version histories.

In practice, mergetools are integrated with version control systems such as Git or Mercurial. For example, Git can be configured to invoke a chosen mergetool when merge conflicts occur, using commands like git mergetool. Users typically resolve each conflicted file in the tool and save, after which Git completes the merge.

Common examples include Meld, KDiff3, Beyond Compare, Araxis Merge, P4Merge, WinMerge, and opendiff on macOS. Many tools are cross-platform and offer either graphical or terminal interfaces.

Limitations include the impossibility of automatic resolution for complex conflicts, the need for manual intervention, and performance on large repositories. They are complementary to diff utilities and are one part of a broader workflow for collaborative software development.