Three-Way Merge & Commit DAG Simulator

Target Line

Next commit edits line 1

Commits

Merge Status

Create commits on both branches, then merge.

Working File

Graph Stats

Total commits

Merge base

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Main ahead by

Feature ahead by

How it works

A repository is a directed acyclic graph (DAG) of commits: every commit points to its parent(s). Two commits diverge when they share a common history but each has commits the other lacks.

merge-base(A, B):
  ancestors(A) = walk parent pointers from A
  for c in walk from B:
    if c in ancestors(A): return c   # first shared commit

That shared commit is the merge base (lowest common ancestor). Git's real algorithm is exactly this ancestor-set walk, just over multi-parent graphs.

three-way merge(base, ours, theirs):
  for each line i:
    if ours[i] == theirs[i]:        keep it (both agree)
    elif ours[i] == base[i]:        take theirs[i]   (only they changed it)
    elif theirs[i] == base[i]:      take ours[i]      (only we changed it)
    else:                           CONFLICT — both changed line i differently

Target line slider — picks which line of the shared file your next commit edits.
Commit on main / Commit on feature — appends a real commit node to that branch's chain, diverging from the merge base the first time both branches have commits.
Merge — computes the merge base via ancestor walk, diffs both branches' edits against it, auto-merges non-overlapping lines, and flags true conflicts (same line, different text) for manual resolution — pick "ours" or "theirs" per conflicting line, then complete the merge to create a two-parent merge commit.

This is the same mechanism behind git merge, git merge-base, and the 3-way diff engine (diff3) that powers every pull-request merge on GitHub/GitLab.

main branch feature branch merge commit

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