montimage/branch-inspector

Branch Inspector

Inspects a single git branch against main to support a cleanup decision. The skill produces a deep overview of what the branch contains, surfaces signals that inform the keep/delete/archive/PR decision, asks the user to choose, then emits a concrete action plan for the chosen path.

When to use

• The user is cleaning up branches and wants to understand one before acting on it.
• The user names a specific branch ("look at feature/foo", "is experiment/x worth keeping?").
• The user wants a deep summary of what a branch implements before deciding its fate.

Do not use this skill for: scanning many branches at once, full repo audits, or reviewing a PR diff line-by-line.

Inputs

The branch name is passed as an argument. If the user invokes the skill without one, ask which branch to inspect — do not default to the current branch silently.

The branch may be local (feature/foo), remote (origin/feature/foo), or both. Detect which exist and report both states.

Prerequisites

Verify before running. Stop and tell the user if any check fails.

• Current directory is a git repository (git rev-parse --git-dir succeeds).
• main branch exists locally or on origin (git rev-parse --verify main or origin/main). If the project's primary branch is master or something else, ask the user to confirm the comparison base.
• The target branch exists locally or on origin. If neither, stop and tell the user.
• gh CLI is optional; used to detect linked PRs. If not available, skip the PR-check step rather than failing.

Repo Sync Before Inspect (mandatory)

Inspection is read-only on the working tree but needs fresh refs to be accurate. Before inspecting:

git fetch origin --prune

--prune removes stale remote-tracking refs so the skill doesn't report a branch as "exists on remote" when it was deleted upstream. Do not check out the branch and do not modify the working tree during inspection.

Workflow

1. Resolve the branch

Given the branch name, determine:

• Does it exist locally? (git rev-parse --verify <branch>)
• Does it exist on remote? (git rev-parse --verify origin/<branch>)
• Are local and remote in sync, or has one diverged from the other?

Pick the inspection target: prefer the local ref if both exist and are in sync, otherwise inspect each side separately and call out the divergence.

2. Build the overview

Collect signals across five groups: identity & activity, merge status, diff scope, implementation depth, staleness. Run independent git commands in parallel where possible. See references/overview-fields.md for the exact field list, the git commands per field, and how to use git cherry for squash-merge detection. The implementation-depth group is the one that matters most for the decision — go beyond stats and read the diff to explain what the branch does. If the diff is too large to read in full, spawn an Explore subagent rather than skimming superficially.

3. Present the overview

Output a structured report. Use this template:

◆ Branch Overview: <branch>
··································································
  Refs:               local=<yes/no> remote=<yes/no> in-sync=<yes/no>
  Tip:                <sha-short> <date> by <author>
  Diverged at:        <sha-short> <date>
  Activity:           <N> commits ahead, <M> commits behind main
                      last commit <X> days ago
  Authors:            <list>
  Diff:               <files> files, +<added>/-<removed> lines
  Top areas:          <dir1>, <dir2>, <dir3>
  Merge status:       <merged | squash-merged | unmerged>
                      cherry-equivalent: <K>/<N> commits already on main
  Linked PR:          <url or "none">
  Conflict risk:      <low | medium | high — files overlap recent main activity>
  Staleness:          <fresh | stale (>30d) | abandoned (>90d)>
  Intent:             <feature | refactor | bugfix | experiment | WIP | unclear>

What this branch implements:
<2-6 sentences describing the actual change, drawn from the diff>

Notable findings:
- <signal 1, e.g., "Adds X module under src/foo, no tests">
- <signal 2, e.g., "Last 3 commits are 'WIP', no rebase since main moved 47 commits">
- <signal 3>

Recommendation: <delete | archive | open PR | keep>
Reasoning: <one sentence>

The recommendation is a suggestion, not a decision. Always defer to the user.

4. Ask the user to decide

Present four options explicitly:

1. Delete — branch is obsolete, already merged, or abandoned with nothing worth saving.
2. Archive — preserve the work but get it out of the active branch list.
3. Open a PR — branch is ready or close to ready for review.
4. Keep — branch is still in active development; no action now.

Ask the user which path to take. Do not act until they answer.

If the user picks Archive, follow up with: "Tag-and-delete (archive/<branch> tag, then delete branch) or rename to archive/<branch>?" Do not assume.

5. Emit the action plan

Once the user has decided, output a numbered action plan with the exact commands. Do not execute them automatically — this is a cleanup workflow and the user should run the commands themselves or explicitly approve.

See references/action-plans.md for the four plan templates (delete, archive tag-and-delete, archive rename, open PR, keep). Pick the template matching the user's decision, substitute <branch>, and present the numbered steps to the user. For the PR template, fill in the title and body from the implementation summary built in step 2.

6. Stop

The skill emits the plan and stops. Executing destructive commands (branch -D, push --delete) is the user's call, not the skill's. If the user explicitly asks the skill to run the plan, confirm once before each destructive step.

Step Completion Reports

Emit a report after the overview phase and after the plan phase.

◆ Branch Overview (step 1 of 2 — <branch>)
··································································
  Refs resolved:      √ pass
  Merge status:       √ pass
  Diff analyzed:      √ pass
  Implementation:     √ pass (deep read)
  PR check:           √ pass (or — gh CLI not available)
  ____________________________
  Result:             PASS

◆ Action Plan (step 2 of 2 — decision: <delete|archive|pr|keep>)
··································································
  Decision captured:  √ pass
  Plan emitted:       √ pass
  Commands listed:    √ pass
  ____________________________
  Result:             PASS

Expected output

A complete run produces three artifacts in the chat, in order:

1. Branch Overview block matching the template in step 3 (refs, tip, activity, diff, merge status, linked PR, conflict risk, staleness, intent, "What this branch implements" prose, notable findings, recommendation).
2. Decision prompt listing all four options (delete / archive / open PR / keep). For archive, a follow-up prompt asking tag-and-delete vs rename.
3. Action plan — the numbered template from references/action-plans.md matching the user's choice, with <branch> substituted and (for PR) suggested title/body filled in.

See references/example-output.md for a worked example showing the overview block, decision prompt, and follow-up plan for an archived branch.

Acceptance criteria

A run is correct when all of these hold:

• The skill ran git fetch origin --prune before reading any refs.
• The branch was resolved on both local and remote; divergence (if any) was reported.
• The Overview block contains every field listed in the step 3 template, with no <placeholder> left unfilled.
• Merge status was determined using git cherry main <branch> (squash-detection), not just git branch --merged.
• The "What this branch implements" prose is grounded in the actual diff — it names files, modules, or functions that appear in git diff main...<branch>.
• All four decision options were presented; if archive was chosen, the tag-vs-rename follow-up was asked.
• The emitted action plan matches references/action-plans.md for the chosen decision, with <branch> substituted.
• No destructive command (branch -D, push --delete, tag) was executed by the skill itself.

Edge cases

• No main branch. Repos using master, develop, or trunk — ask once and use the answer for the rest of the run.
• Branch only exists on remote. Inspect origin/<branch> directly; do not check out locally.
• Branch only exists locally. Note "remote=no" and skip linked-PR check.
• Branch is identical to main. Report 0 commits ahead and recommend delete.
• Branch is fully squash-merged. git branch --merged says no but git cherry shows all - lines — recommend delete and call out the squash detection.
• Diff too large to read in full. Spawn an Explore subagent to summarize rather than skimming superficially. Note in the overview that the summary is from a subagent.
• Detached HEAD or invalid name. Stop and tell the user; do not guess.
• Active worktree on the branch. Refuse the delete plan; tell the user to remove the worktree first.
• gh CLI not installed. Skip the linked-PR check; mark as "n/a — gh not available". Do not fail the run.
• User refuses to choose. Print the overview, note "decision deferred", and stop.

Notes

• Read-only by default. The skill never deletes, pushes, or rewrites refs on its own. It emits commands; the user runs them.
• Don't trust the branch name. A branch called fix/typo may contain a refactor; always verify intent from the diff, not the name.
• Context budget. For very large diffs, prefer an Explore subagent over reading the full diff in the main context window — summarized findings cost fewer tokens and keep the overview focused.