Overview
Every changed line is a line the reviewer must inspect, a line that could introduce a regression, and a line that will appear in the git blame forever. Unnecessary changes are costly.
AI agents often "improve" adjacent code, reformat files, rename variables for consistency, or delete "dead" code — all without being asked. This creates noisy diffs, unexpected behavior changes, and broken trust.
This skill enforces a hard rule: every changed line must trace directly to the user's request.
When to Use
- Any time you are modifying existing code (not creating new files)
- When your diff is larger than you expected
- When reviewing your own generated changes before presenting them
Process
Step 1: Establish the Change Boundary
- Read the task carefully. Write down exactly which files and functions need to change.
- Draw a mental boundary: "Everything outside this boundary is out of scope."
- List what you will NOT change, even if you'd do it differently:
- Adjacent functions
- Variable naming conventions
- Comment style
- Import order
- Formatting/whitespace (unless fixing a specific bug)
Verify: You can name the specific functions/lines that need to change.
Step 2: Make Only the Required Changes
- Make the changes — and only the changes — within the defined boundary.
- If you notice something wrong outside the boundary:
- Mention it in a comment — don't fix it silently
- Example: "Note: I noticed
fetchUserhas no error handling, but I'm leaving that for a separate PR."
- If your changes made imports/variables/functions unused: remove only those created by YOUR changes. Leave pre-existing dead code alone (unless asked).
Verify: No line changed that wasn't part of the defined scope.
Step 3: Review Your Own Diff
- Read through your diff line by line.
- For each changed line, ask: "Why did I change this?"
- If you can't answer → revert it
- Flag any changes that are purely cosmetic and ask: "Should I include this?"
Verify: Every changed line has a clear reason directly tied to the task.
Step 4: Document Scope Decisions
- In your PR/commit message, explicitly note what you chose NOT to change and why:
- "Did not refactor the adjacent
parseDatefunction — out of scope for this fix."
- "Did not refactor the adjacent
Common Rationalizations (and Rebuttals)
| Excuse | Rebuttal |
|---|---|
| "I improved it while I was there" | That's a separate PR. Drive-by improvements hide bugs and inflate diffs. |
| "The old comment was wrong" | Fix comments related to your change. Leave others for a documentation PR. |
| "I made the code more consistent" | Consistency PRs should be standalone. Don't bundle them. |
| "It's just whitespace" | Whitespace changes cause merge conflicts and obscure real diffs in blame. |
| "The dead code is obviously wrong" | File an issue. Don't delete pre-existing code without explicit approval. |
Red Flags
- Your diff is 3× larger than the feature size suggests
- You changed files that aren't related to the task
- You reformatted a file "while you were there"
- You renamed variables for consistency
- You deleted comments or code you didn't fully understand
- Your PR description says "and also fixed a few other things"
Verification
- Every changed line traces to the task description
- No cosmetic-only changes bundled in (or explicitly approved)
- Pre-existing dead code left untouched (or flagged, not deleted)
- Changes to adjacent unrelated code: zero
- Diff size is proportional to task size
References
- simplicity-first skill
- code-review skill
- Karpathy: "They still sometimes change/remove comments and code they don't sufficiently understand as side effects, even if orthogonal to the task."
