focused-fix

Testing & Quality

This skill should be used when the user asks to "fix a bug with minimal changes", "analyze change scope for a bugfix", "find the minimal set of files to change", "do a focused bugfix", or "scope a minimal repair".

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Focused Fix

Category: Engineering Domain: Debugging & Maintenance

Overview

The Focused Fix skill enforces a disciplined minimal-change approach to bug fixing. Instead of refactoring or improving code during a bugfix, it identifies the smallest possible change set that resolves the issue. This reduces risk, simplifies code review, and prevents scope creep.

Use when

The user asks to "fix a bug with minimal changes", "do a focused bugfix", or "scope a minimal repair"
A bug report needs triage to identify the smallest set of files to touch
A PR is at risk of scope creep (unrelated refactors, style changes, "nearby" fixes)
A hotfix or release-blocker needs a low-risk, reviewable change set
The user asks "what is the minimal change to fix X?" or "which files do I need to touch for this bug?"

Clarify First

Before scoping the fix, confirm these inputs. If any is unknown or vague, ASK — do not assume:

Observable failure — the exact symptom, repro steps, and expected vs actual behavior (the bug description the analyzer matches against, and what the fix must resolve — not a guess at the cause)
Codebase path & file types — which directory and extensions to search (sets --path/--extensions)
Minimal vs structural — confirm this is a focused fix, not a refactor (determines whether out-of-scope "while I'm here" changes are rejected)

Stop rule: ask only the 2-3 that most change the output. If the user says "just draft it," proceed and list your assumptions at the top of the artifact.

Quick Start

# Analyze a bug description to identify minimal change scope
python scripts/change_scope_analyzer.py --bug "Login fails when email has + character" --path ./src

# Analyze with JSON output
python scripts/change_scope_analyzer.py --bug "API returns 500 on empty array input" --path ./src --format json

# Analyze with specific file extensions
python scripts/change_scope_analyzer.py --bug "CSS overflow on mobile" --path ./src --extensions .css .scss .html

Tools Overview

Tool	Purpose	Key Flags
`change_scope_analyzer.py`	Identify minimal files to change for a bugfix	`--bug`, `--path`, `--extensions`, `--format`

change_scope_analyzer.py

Analyzes a bug description against a codebase to identify:

Files most likely related to the bug (keyword matching, import tracing)
Estimated change scope (number of files, lines)
Risk assessment for the change
Recommended fix approach (minimal vs. structural)

Workflows

Focused Bugfix Workflow

Write a clear bug description — reproduction steps, expected vs actual behavior
- Validate: the description names the observable failure, not a guess at the cause
Run change_scope_analyzer.py to identify scope
- Validate: analyzer output lists concrete files and an estimated line count
Review the recommended files and approach
- Validate: recommended approach is "minimal" — if it says "structural", stop and scope a refactor PR separately
Make ONLY the changes needed to fix the bug
- Validate: git diff --stat matches (or is smaller than) the analyzer's recommendation
Verify no unrelated changes leaked in
- Validate: git diff shows no formatting-only changes, no unrelated imports, no "while I'm here" edits
Submit PR with focused change set
- Validate: commit message states the exact bug fixed, and a regression test is included

Scope Validation

After making changes, re-run analyzer
Compare actual changes against recommended scope
Flag any out-of-scope modifications for separate PRs
- Validate: any file touched that was not in the analyzer recommendation has a one-line justification or is reverted

Reference Documentation

Focused Fix Methodology - Principles, anti-patterns, and decision framework

Common Patterns

Do

Fix the exact bug reported
Add a regression test for the fix
Document why the fix works in the commit message
Keep the diff as small as possible

Don't

Refactor surrounding code during a bugfix
Fix "nearby" issues in the same PR
Change formatting or style in touched files
Add features disguised as bugfixes

Anti-patterns

Anti-pattern	Failure mode	Fix
"While I'm here" refactors in the bugfix PR	Blast radius explodes; review time multiplies; unrelated regressions masked by the real fix	Open a separate PR for the refactor, tagged as `refactor:` not `fix:`
Reformatting or auto-save style changes in touched files	Diff becomes unreadable; real fix hidden in 200 lines of whitespace	Revert style changes before committing; configure the editor to format-on-save only for new files
Fixing the symptom in the wrong layer	Bug returns in a new form; accumulates workaround debt	Trace to the root layer — analyzer's keyword-match output is a hint, not an answer
Skipping the regression test "because the fix is obvious"	Bug silently returns on a refactor 6 months later	Every `fix:` commit adds at least one failing-then-passing test
Treating `change_scope_analyzer.py` output as authoritative	Analyzer is keyword/import-based, not semantic — misses dynamic dispatch, reflection, config-driven paths	Use it as a starting set; grep for callers and tests before committing to the scope
Bundling the fix with a dependency upgrade	Two risk profiles in one PR; if rollback is needed, both are lost	Land the upgrade separately, then the fix against the upgraded baseline