Remove a Co-authored-by trailer from recent commits

Source: gh-collab-manager/server.js — /api/repos/:owner/:repo/remove-coauthor Category: Snippet — git

Co-author trailer removal — Git’s Co-authored-by: footer in commit messages drives GitHub’s contributor attribution. Adding one on purpose is easy; removing one after the fact means rewriting commit messages. Here’s the recipe.

The trailer

A commit message with co-authorship looks like:

Fix admin project link field — normalize scheme on save

The form used input type=url (required a scheme) but the renderer
prepends https:// to whatever's stored.

Co-authored-by: Claude Opus 4.6 (1M context) <[email protected]>

GitHub reads Co-authored-by: lines in the last paragraph of a commit message and attributes the commit to both people.

Remove from the most recent commit

git commit --amend --message "$(git log -1 --pretty=%B | grep -v '^Co-authored-by:')"
git push --force-with-lease

git log -1 --pretty=%B — print the full message of HEAD
grep -v '^Co-authored-by:' — strip any line starting with that trailer
--amend --message — replace HEAD’s message with the filtered one
--force-with-lease — safer force push (refuses if the remote has new commits)

Remove from the last N commits

git filter-branch --msg-filter 'grep -v "^Co-authored-by:"' HEAD~10..HEAD

Rewrites the last 10 commits, stripping the trailer from each. filter-branch is deprecated in modern git; use git filter-repo for anything bigger than a quick one-off.

Modern equivalent with git filter-repo:

# Install: pip install git-filter-repo
git filter-repo --message-callback '
  return b"\n".join(
    line for line in message.split(b"\n")
    if not line.startswith(b"Co-authored-by:")
  )
'

Remove one specific co-author, keep others

git filter-branch --msg-filter 'grep -v "^Co-authored-by: Bot Name <[email protected]>"' HEAD~N..HEAD

Matches the exact trailer line. Use when you co-authored to one of several people and want to drop just one.

Programmatic (what gh-collab-manager does)

async function removeCoauthor(owner, repo, coauthorEmail) {
  const tmpDir = await fs.mkdtemp(join(tmpdir(), 'coauthor-'));
  await execFileAsync('git', ['clone', `https://github.com/${owner}/${repo}`, tmpDir]);

  await execFileAsync('git', [
    '-C', tmpDir,
    'filter-branch', '-f',
    '--msg-filter',
    `grep -v '^Co-authored-by:.*<${coauthorEmail}>$' || true`,
    'HEAD~50..HEAD',
  ]);

  await execFileAsync('git', ['-C', tmpDir, 'push', '--force-with-lease', 'origin', 'main']);
  await fs.rm(tmpDir, { recursive: true, force: true });
}

|| true after grep handles the case where no lines match (grep exits 1); we want the filter to succeed even if nothing was filtered.

Gotchas

This rewrites history. Everyone who cloned the repo will have diverging history on their next pull. Fine for single-author personal repos; never do this on collaborative branches without coordination.
--force-with-lease, not --force. Lease refuses to overwrite new commits pushed by someone else; --force silently nukes them.
CI runs again. Every rewritten commit triggers its CI workflow. Be sure the workflow is idempotent and rate-limit friendly.
PR references break. If commits were referenced by SHA in issues / discussions, those links go dead. filter-branch changes every SHA from the rewrite point.
Backup the repo first. cp -r repo repo.backup or push a backup-<date> branch before doing this on anything you care about.
The email match matters. Different commit tools embed the bot email differently (display name variations, extra whitespace). Test the grep against real commits before running it destructively.
Signed commits get unsigned. filter-branch strips GPG signatures. Re-sign after or skip signed commits.
git filter-repo is the modern tool. filter-branch is deprecated for good reason — it’s slow and has footguns. For ongoing use, install filter-repo.
GitHub Actions attribution cache. GitHub caches contributor lists; removing a coauthor doesn’t immediately remove them from the UI. Give it 24 hours.