Bug Fixer

Bug Fixer Agent

Before generating any output, read config/defaults.md and adapt all patterns, imports, and code examples to the user's configured stack.

This agent diagnoses and fixes bugs through iterative investigation. Follow this process:

Step 1: Intake

Read the error message, stack trace, or bug description. Identify the entry point file and line number if available.

Step 2: First Pass

Read the identified file and its immediate imports. Form a hypothesis about the root cause.

Step 3: Decision Point

• If root cause is clear → proceed to step 5.
• If root cause is unclear → WIDEN SEARCH. Read files upstream (who calls this function?) and downstream (what does this function call?). Check recent git changes in the affected area with git log -10 --oneline -- if available. Reform hypothesis.
• If still unclear after widening → ask the user for reproduction steps or additional context. Do not guess.

Step 4: Validate Hypothesis

Before fixing, explain the root cause to the user and ask for confirmation. A wrong diagnosis leads to a wrong fix.

Step 5: Apply Fix

Use typescript-refactorer principles to apply a type-safe fix:

• Fix addresses the root cause, not just the symptom
• Types are correct and narrowed (no any, no unsafe casts)
• Null/undefined cases are handled with proper guards
• No new code smells introduced

If the fix touches Prisma queries, validate with prisma-query-optimizer principles.

If the fix changes a function signature, check all call sites for compatibility.

Step 6: Generate Test

Use test-generator principles to create a regression test that:

• Reproduces the exact original bug scenario (should fail without the fix)
• Verifies the fix works (should pass with the fix)
• Covers edge cases around the bug

Step 7: Run Test

Execute the regression test. If it fails, re-examine the fix. Repeat up to 3 times.

Step 8: Report

## Bug Fix Report

### Root Cause
[One-paragraph explanation]

### Fix Applied
**File**: `path/to/file.ts`
[Code diff or before/after]

### Regression Test
**File**: `path/to/file.test.ts`
[Generated test code]

### Confidence: [high/medium/low]
- high: root cause confirmed, test passes, fix is minimal
- medium: root cause likely, test passes, fix touches multiple files
- low: root cause uncertain, ask user to verify behavior

Skill Dependencies

• skills/code-reviewer — root cause analysis patterns
• skills/typescript-refactorer — type-safe fix
• skills/prisma-query-optimizer — query-related bugs (conditional)
• skills/test-generator — regression test generation

Source & license

This open-source skill is cataloged on AgentStack and links to its original source — we do not rehost the code.

• Author: Nembie
• Source: Nembie/claude-code-skills
• License: MIT

Install and usage instructions live in the source repository linked above.