Code Investigate Skill
Trigger
- Keywords: investigate code, how feature works, trace implementation, dual confirmation, deep dive, how code works, what this code does, code research
When NOT to Use
- Just need quick lookup (use Grep/Glob directly)
- Code review (use codex-review)
- System verification (use feature-verify)
- Git history tracking (use git-investigate)
Core Principle
Codex must explore independently. Feeding Claude's conclusions to Codex is prohibited.
┌─────────────────┐ ┌─────────────────┐
│ Claude Explores │ │ Codex Explores │
│ Independently │ │ Independently │
│ (Phase 1-2) │ │ (Phase 3) │
└────────┬────────┘ └────────┬────────┘
│ │
▼ ▼
┌───────────┐ ┌───────────┐
│ Claude │ │ Codex │
│ Conclusion│ │ Conclusion│
└─────┬─────┘ └─────┬─────┘
│ │
└───────────┬───────────┘
▼
┌─────────────┐
│ Consolidated│
│ Report │
│ (Phase 4) │
└─────────────┘
Workflow
| Phase |
Name |
Action |
Output |
| 1 |
Claude Explore |
Grep/Glob/Read to search code |
Related files list |
| 2 |
Claude Conclude |
Analyze logic, form understanding |
Initial conclusion (internal) |
| 3 |
Codex Explore |
Invoke Codex MCP to explore independently |
Codex analysis report |
| 4 |
Integrate |
Compare both perspectives, mark differences |
Consolidated report |
Codex Invocation Rules
Required Parameters
| Parameter |
Value |
Description |
sandbox |
read-only |
Force read-only |
approval-policy |
never |
Auto-execute |
cwd |
Project root |
Exploration start point |
Correct Approach
mcp__codex__codex({
prompt: `# Code Investigation Task
## Question
${userQuestion}
## Project Info
- Path: ${cwd}
- Tech Stack: {FRAMEWORK} + TypeScript + {DATABASE}
Please **independently explore** the codebase and answer:
1. What files are related?
2. How does the core logic work?
3. What is the data flow?
4. What are the key dependencies?
Please grep/read and explore on your own, then provide your analysis.`,
cwd: '/path/to/project',
sandbox: 'read-only',
'approval-policy': 'never',
});
Prohibited Approaches
| Pattern |
Problem |
Example |
| Feeding conclusion |
Claude's findings leak to Codex |
Claude found these files: ${findings} |
| Leading question |
Presupposes answer |
I think the problem is in cache, verify |
| Scope restriction |
Prevents independent exploration |
Only look at src/service/ |
Verification Checklist
| Check |
Standard |
| Claude independent conclusion |
Phase 2 forms conclusion, not output to user |
| Codex prompt is clean |
Contains only question + project path, no Claude findings |
| Report perspectives separated |
Claude / Codex conclusions presented separately |
| Integration is complete |
Marks agreement, differences, possible gaps |
References
| File |
Purpose |
When to Read |
references/prompts.md |
Codex prompt templates |
Before Phase 3 |
references/output-template.md |
Report format |
During Phase 4 |
Examples
Feature Investigation
Input: Investigate how order processing works
Phase 1: Grep "processOrder" -> Read src/service/order/*.ts
Phase 2: Form understanding: Controller -> Service -> Repository write
Phase 3: Codex explores independently (only given question + path)
Phase 4: Consolidated report -> mark both perspectives
Mechanism Understanding
Input: How does the API caching mechanism work?
Phase 1: Grep "cache" + "portfolio" -> Read related files
Phase 2: Understand Redis TTL + fallback mechanism
Phase 3: Codex investigates independently
Phase 4: Compare differences -> output consolidated report
Problem Diagnosis
Input: Why is token price sometimes null?
Phase 1: Search price-related logic + error handling
Phase 2: Identify possible fallback paths
Phase 3: Codex diagnoses independently
Phase 4: Synthesize both findings -> list possible causes
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