Split a fat branch

You started with one branch, kept committing, and ended up with seven commits that really should be three reviewable PRs. sm split is the verb.

Starting state

main
└── feat/auth-everything   (current)
       7 commits:
         1. models: add User
         2. models: add Session
         3. models: tests
         4. handlers: /login
         5. handlers: /logout
         6. handlers: tests
         7. docs: auth README

You want three branches:

main
└── feat/auth-models   (commits 1-3)
    └── feat/auth-handlers   (commits 4-6)
        └── feat/auth-docs   (commit 7)

Step 1 — see the commit indices

sm show

The Commits: section lists them 1-based, oldest first. (You can also use git log --reverse --oneline main..HEAD if you prefer.)

Step 2 — split with explicit ranges

sm split \
  --names auth-models,auth-handlers,auth-docs \
  --commits "1-3,4-6,7"

Output:

✓ split feat/auth-everything into 3 branch(es):
  feat/auth-models
  feat/auth-handlers
  feat/auth-docs

After this, feat/auth-everything is replaced by the chain above. HEAD is on the topmost new branch (feat/auth-docs). sm log confirms:

stac-man

main
└─ feat/auth-models
   └─ feat/auth-handlers
      └─ feat/auth-docs  ← current

Step 3 — submit as a stack

sm submit --stack

Three PRs, bases wired correctly:

PR	Branch	Base
#1	feat/auth-models	main
#2	feat/auth-handlers	feat/auth-models
#3	feat/auth-docs	feat/auth-handlers

Variations

Auto split (one branch per commit)

If the commit subjects are already meaningful, drop the flags:

sm split

Each commit becomes a branch named after its slugified subject (models-add-user, models-add-session, …). Useful for small chains; rename afterward if you don't like the auto names.

Per-hunk split

Not supported. If you committed two unrelated changes in one commit, undo the commit first, then re-stage and re-commit each chunk separately. Substitute real commit messages for "<message-a>" / "<message-b>":

git reset --soft HEAD^
git add -p     # interactively pick hunks for commit A
git commit -m "<message-a>"
git add .      # the rest go into commit B
git commit -m "<message-b>"
sm split --names a,b --commits "1,2"

Recovery

Don't like the result? sm undo rewinds the split:

sm undo

Your original feat/auth-everything comes back with all seven commits.

See also

• sm split — flag reference.
• sm fold — the inverse direction.
• Recipes → Absorb fixups — for the "I added one fixup commit and want it in commit 3" version of this problem.