How to compare two Git branches with diff

Comparing Git branches before a merge shows which files and lines differ between the target branch and the work being reviewed. This catches unrelated changes, missing files, and review-scope drift before a pull request, release merge, or handoff.

The command git diff compares tree states. The two-dot form, such as main..feature/docs, compares the current tips of both branches, while the three-dot form, such as main...feature/docs, compares the merge base with the second branch.

Use branch names or remote-tracking refs that exist in the repository. Fetch remote refs before comparing them, and remember that committed branch comparisons do not include uncommitted working-tree edits.

1. Confirm that both branch references exist in the repository.

   $ git branch --list main feature/docs
     feature/docs
   * main

   Replace main and feature/docs with the branch names being compared. Use remote-tracking names such as origin/main after fetching from the remote.

2. Compare the current branch tips when the exact end-state difference matters.

   $ git diff --name-status main..feature/docs
   M	docs/guide.md
   A	docs/release-notes.md
   D	docs/security.md

   git diff main..feature/docs is the same branch-tip comparison as git diff main feature/docs. The D row means the file exists at the tip of main but not at the tip of feature/docs.

3. Compare the feature branch from its merge base with the target branch.

   $ git diff --name-status main...feature/docs
   M	docs/guide.md
   A	docs/release-notes.md

   Use the three-dot form for the usual review view of what feature/docs introduced since it split from main.

4. Print a compact summary of the reviewed branch changes.

   $ git diff --stat main...feature/docs
    docs/guide.md         | 3 ++-
    docs/release-notes.md | 2 ++
    2 files changed, 4 insertions(+), 1 deletion(-)

5. Review the full patch for the branch or a specific path.

   $ git diff main...feature/docs -- docs/guide.md
   diff --git a/docs/guide.md b/docs/guide.md
   index 073e1ba..692f29f 100644
   --- a/docs/guide.md
   +++ b/docs/guide.md
   @@ -1,3 +1,4 @@
    Title: Deployment guide
   -Status: draft
   +Status: reviewed
    Owner: platform
   +Review checklist: compare branches before merge

   The -- separator tells Git that the remaining argument is a path, which helps when a file name could also be parsed as a revision.