Codex Implement Skill

Trigger

• Keywords: codex implement, implement feature, codex write code, implement from spec

When NOT to Use

• Architecture advice only (use /codex-architect)
• Code review (use /codex-review-fast)
• Bug fix (use /bug-fix)
• Simple one-line change (edit directly)

Workflow

Parse args → Decompose → Collect context → Iterate items → Review loop → Done
                                              ↕
                                    codex → diff → confirm
                                              ↕
                                    reject/modify → codex-reply

Step 1: Parse & Decompose

--spec provided: Read spec/request doc, extract individual items. Arguments without --spec: Use directly as single item. No arguments: Ask user for requirement, target file, reference files.

Break into implementation items — each one logical unit (interface, method, endpoint), implementable in dependency order, small enough for one Codex call.

Present plan before starting:

| # | Item              | Target File          | Depends On |
|---|-------------------|----------------------|------------|
| 1 | Define interfaces | src/interface/x.ts   | -          |
| 2 | Core logic        | src/service/x.ts     | 1          |
| 3 | Controller/Route  | src/controller/x.ts  | 2          |

Proceed?

Step 2: Collect Context (Claude, NOT Codex)

Claude researches the codebase before calling Codex:

1. Read .claude/CLAUDE.md (fallback CLAUDE.md) — tech stack, conventions, test commands
2. Read target file (if exists) and context files
3. Search similar implementations
4. Read 2-3 similar files for patterns

Summarize as PROJECT_CONTEXT for Codex.

Step 3: Iterative Implementation

Implement one item at a time, in dependency order.

3a: First item — new session

See references/codex-prompts.md for the full prompt template.

Call mcp__codex__codex with sandbox: 'workspace-write', approval-policy: 'on-failure'.

Save the returned threadId.

3b: Confirm each item

After each Codex call: git diff → ask user:

3c: Subsequent items — same thread

Use mcp__codex__codex-reply with saved threadId. See references/codex-prompts.md.

Repeat 3b → 3c until all items done.

Step 4: Final Confirmation

git diff full changeset → user confirms.

Step 5: Review Loop (Codex-in-the-loop)

⚠️ @CLAUDE.md auto-loop: fix → re-review → ... → ✅ PASS ⚠️

Issues found → use same Codex thread to fix (not manual). See references/codex-prompts.md for fix prompt.

Max 3 rounds per step. Still failing → report blocker.

Test Requirements

If Codex omitted tests → codex-reply to request them.

Output

## Codex Implementation Report

### Implementation Items

| # | Item | Target File | Status |
|---|------|-------------|--------|
| 1 | ...  | ...         | ✅/❌  |

### Change Summary

| File | Operation | Description |
|------|-----------|-------------|
| ...  | Create/Modify | ...     |

### Review Result
<codex-review-fast output>

### Gate
✅ Complete / ⛔ Needs modification

Verification

• All items implemented and confirmed
• Tests included for each item
• /codex-review-fast passed
• /precommit passed

Examples

/codex-implement "Add a method to calculate fees"
/codex-implement "Implement wallet service" --spec docs/features/wallet/2-tech-spec.md
/codex-implement "Add getUserBalance method" --target src/service/wallet.service.ts
/codex-implement "Implement cache logic" --target src/service/cache.ts --context src/service/redis.ts