Code Investigator

Code Investigator

Systematically investigate code to understand specifications and provide evidence-based reports with file/line references. Saves findings to persistent memory for future reference.

Core Capabilities

1. Evidence-based specification confirmation: Trace code to confirm actual behavior with file/line references
2. Visual flow documentation: Generate Mermaid diagrams for multi-file/complex flows
3. Persistent memory storage: Save investigation results in searchable format for future use
4. Uncertainty tracking: Clearly distinguish confirmed facts from unknowns

Investigation Workflow

Step 0: Plan (Brief)

State what to investigate and where to start (1-3 lines). Prevents scope drift.

Step 1: Identify Entry Point

Locate the starting point: routing, CLI entry, UI event, main function, service initialization, etc.

Step 2: Trace Call Chain (Shortest Path Only)

Follow function/class/module calls related to the specification. Identify:

• Data structures (DTO/Model/State) and transformation points
• Conditional logic, defaults, exception handling, retries, caching, persistence

Step 3: Extract Confirmed Specifications

Document facts that can be determined from code:

• "When/If [condition] then [action]"
• Default values, timeout settings, retry counts, etc.

Step 4: Handle Uncertainties

List runtime dependencies (env vars, config files, external APIs) that cannot be confirmed from code alone:

• Mark as "Unconfirmed"
• Suggest additional investigation methods

Step 5: Generate Diagram (Conditional)

Create Mermaid diagram when:

• 3+ files are involved
• Async/event-driven/state transitions are present
• Dependency direction is unclear (DI, plugins, hooks)

Output Format

Use this template for all investigation reports:

Report Template

## TL;DR
[1-2 sentence conclusion]

## Confirmed Specifications
[Bulleted list, each with evidence]

- **Spec**: [When/If/Then format]
  - **Evidence**: [path/to/file.ts:L10-L42](path/to/file.ts#L10-L42) - [Why this code proves the spec]
  - **Notes**: [Optional: exceptions, config dependencies, related locations]

## Implementation Evidence
[Key implementation details by file]

### [path/to/file.ts](path/to/file.ts)
- Lines X-Y: [What this code does]
- Lines A-B: [What this code does]

## Flow Diagram (Optional)
[Mermaid diagram if applicable]

## Open Questions / Unknowns
[What could not be confirmed and why]
- [Unconfirmed item]: [What additional investigation is needed]

Evidence Linking Rules

• Always link files with markdown: [path/to/file.ts](path/to/file.ts#L10-L42)
• Use line numbers when available: #L10-L42
• If line numbers unavailable, use: #functionName or just (file.ts)

Specification Item Format

Every specification MUST follow this structure:

• Spec: Specification statement (prefer When/If/Then format)
• Evidence: File reference + one-line justification
• Notes (optional): Exceptions, config dependencies, related code

Diagram Guidelines

Use appropriate diagram types:

• Process flow: sequenceDiagram
• Module dependencies: flowchart LR
• State transitions: stateDiagram-v2

Diagram policy:

• Show shortest path only (no comprehensive views)
• Use File::Symbol format for node names (e.g., src/foo.ts::createPlayer)

Example:

sequenceDiagram
    participant UI as app/routes/_app.tsx::handleClick
    participant Store as app/stores/player.ts::Player
    participant Service as app/lib/player/service.ts::updateState
    
    UI->>Store: dispatch(action)
    Store->>Service: updateState(data)
    Service-->>Store: newState

Memory Storage

All confirmed investigations are saved to: .claude/skills/code-investigator/memories/

Storage Timing

• Save when specification is confirmed (even partial)
• Save incomplete results with status in-progress

File Naming Convention

YYYY-MM-DD__topic__short-slug.md

Example: 2026-01-08__player__loop-behavior.md

Memory File Format

---
summary: "Brief description of investigation topic and findings"
created: YYYY-MM-DD
updated: YYYY-MM-DD  # optional
status: confirmed | in-progress | blocked  # optional
tags: [feature-area, component]  # optional
related: [path/to/file.ts, path/to/other.ts]  # optional
---

# [Investigation Topic]

## Question
[Original user question or investigation goal]

## Confirmed Specifications
[Same format as report above]

## Implementation Evidence
[Same format as report above]

## Flow Diagram
[Mermaid if applicable]

## Open Questions
[Unconfirmed items and next steps]

Language: All memory files MUST be written in English (per project standards). Chat responses can be in Japanese.

Memory Search Workflow

When asked to recall previous investigations:

# 1. List investigations
ls .claude/skills/code-investigator/memories/

# 2. View all summaries
rg "^summary:" .claude/skills/code-investigator/memories/ --no-ignore --hidden

# 3. Search summaries by keyword
rg "^summary:.*keyword" .claude/skills/code-investigator/memories/ --no-ignore --hidden -i

# 4. Search by tag
rg "^tags:.*keyword" .claude/skills/code-investigator/memories/ --no-ignore --hidden -i

# 5. Full-text search (when summary insufficient)
rg "keyword" .claude/skills/code-investigator/memories/ --no-ignore --hidden -i

# 6. Read specific memory if relevant

Note: Memory files are gitignored, use --no-ignore --hidden flags.

Quality Standards

Prohibited

• No speculation as fact: Use "likely" / "probably" only in "Open Questions", never in "Confirmed Specifications"
• No baseless evidence: Every specification claim must have file:line reference

Required

• Primary vs supplementary evidence: When multiple locations support one spec, separate "primary" and "supplementary" evidence
• Config/env dependencies: Always note when behavior depends on ENV vars, config files, or runtime values

References

For detailed guidance on specific patterns, see:

• references/report-templates.md - Detailed report format examples
• references/diagram-patterns.md - Mermaid diagram examples for common scenarios

scripts/

Executable code (Python/Bash/etc.) that can be run directly to perform specific operations.

Examples from other skills:

• PDF skill: fill_fillable_fields.py, extract_form_field_info.py - utilities for PDF manipulation
• DOCX skill: document.py, utilities.py - Python modules for document processing

Appropriate for: Python scripts, shell scripts, or any executable code that performs automation, data processing, or specific operations.

Note: Scripts may be executed without loading into context, but can still be read by Codex for patching or environment adjustments.

references/

Documentation and reference material intended to be loaded into context to inform Codex's process and thinking.

Examples from other skills:

• Product management: communication.md, context_building.md - detailed workflow guides
• BigQuery: API reference documentation and query examples
• Finance: Schema documentation, company policies

Appropriate for: In-depth documentation, API references, database schemas, comprehensive guides, or any detailed information that Codex should reference while working.

assets/

Files not intended to be loaded into context, but rather used within the output Codex produces.

Examples from other skills:

• Brand styling: PowerPoint template files (.pptx), logo files
• Frontend builder: HTML/React boilerplate project directories
• Typography: Font files (.ttf, .woff2)

Appropriate for: Templates, boilerplate code, document templates, images, icons, fonts, or any files meant to be copied or used in the final output.

Not every skill requires all three types of resources.