Codex System — Planning, Design & Complex Implementation

Codex CLI handles planning, design, and complex code implementation.

Detailed rules: .claude/rules/codex-delegation.md

Two Roles of Codex

1. Planning & Design

• Architecture design, module composition

• Implementation plan creation (step breakdown, dependency ordering)

• Trade-off evaluation, technology selection

• Code review (quality and correctness analysis)

2. Complex Implementation

• Complex algorithms, optimization

• Debugging with unknown root causes

• Advanced refactoring

• Multi-step implementation tasks

When to Consult (MUST)

Situation Trigger Examples

Planning "Create a plan" "Architecture"

Design decisions "How to design?"

Complex implementation "How to implement?" "How to build?"

Debugging "Why doesn't this work?" "Error" "Debug"

Trade-off analysis "Which is better?" "Compare"

Refactoring "Refactor" "Simplify"

Code review "Review" "Check"

When NOT to Consult

• Simple file edits, typo fixes

• Tasks that simply follow explicit user instructions

• git commit, test execution, lint

• Codebase analysis → general-purpose subagent (Opus 1M context)

• External information retrieval → general-purpose subagent (Opus, WebSearch/WebFetch)

• Multimodal processing → Gemini CLI (PDF/video/audio/images)

How to Consult

Subagent Pattern (Recommended)

Task tool parameters:

• subagent_type: "general-purpose"

• run_in_background: true (optional)

• prompt: | Consult Codex about: {topic}

  codex exec --model gpt-5.4 --sandbox read-only --full-auto " {question for Codex} " 2>/dev/null

  Return CONCISE summary (key recommendation + rationale).

Direct Call (responses up to ~50 lines)

codex exec --model gpt-5.4 --sandbox read-only --full-auto "Brief question" 2>/dev/null

Having Codex Implement Code

codex exec --model gpt-5.4 --sandbox workspace-write --full-auto " Implement: {task description} Requirements: {requirements} Files: {file paths} " 2>/dev/null

Sandbox Modes

Mode Use Case

read-only

Design, review, debug analysis

workspace-write

Implementation, fixes, refactoring

Task Templates

Implementation Planning

codex exec --model gpt-5.4 --sandbox read-only --full-auto " Create an implementation plan for: {feature}

Context: {relevant architecture/code}

Provide:

1. Step-by-step plan with dependencies
2. Files to create/modify
3. Key design decisions
4. Risks and mitigations " 2>/dev/null

Design Review

codex exec --model gpt-5.4 --sandbox read-only --full-auto " Review this design approach for: {feature}

Context: {relevant code or architecture}

Evaluate:

1. Is this approach sound?
2. Alternative approaches?
3. Potential issues?
4. Recommendations? " 2>/dev/null

Debug Analysis

codex exec --model gpt-5.4 --sandbox read-only --full-auto " Debug this issue:

Error: {error message} Code: {relevant code} Context: {what was happening}

Analyze root cause and suggest fixes. " 2>/dev/null

Language Protocol

• Ask Codex in English

• Receive response in English

• Execute based on advice

• Report to user in the user's language

Why Codex?

• Deep reasoning: Complex analysis and problem-solving

• Planning expertise: Architecture and implementation strategies

• Code mastery: Complex algorithms, optimization, debugging

• Consistency: Same project context via context-loader skill