| name | codex-implement |
| description | Implement features via Codex MCP. Use when: writing new code from specs, implementing features, Codex-driven development. Not for: code review (use codex-code-review), architecture advice (use codex-architect). Output: implemented code + review loop. |
| allowed-tools | mcp__codex__codex, mcp__codex__codex-reply, Bash(git:*), Read, Grep, Glob, Edit, Write, AskUserQuestion, Skill, Agent |
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:
- Read
.claude/CLAUDE.md (fallback CLAUDE.md) — tech stack, conventions, test commands
- Read target file (if exists) and context files
- Search similar implementations
- 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:
| Choice | Action |
|---|
| Accept | Proceed to next item (3c) |
| Reject | git checkout . affected files, re-attempt (max 2 retries, then ⛔) |
| Modify | codex-reply with feedback → loop back to 3b |
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 ⚠️
| Step | Command | On fail |
|---|
| 1 | /codex-review-fast | codex-reply to fix → re-review |
| 2 | /precommit | codex-reply to fix → re-run |
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
| Change Type | Required Tests |
|---|
| New service/provider | Unit (happy + error + edge) |
| New API endpoint | Unit + integration |
| Modified logic | Existing pass + new logic tests |
| Bug fix scenario | Regression test |
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
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
