OpenAI Codex CLI vs KiroComparisonUpdated 2026-03-16
SUMMARY
OpenAI Codex CLI (CLI) uses markdown configuration while Kiro (IDE) uses markdown. They differ on 3 of 11 compared features. Both tools provide AI-assisted development but take different approaches to project configuration.
FEATURE COMPARISON
| Feature | OpenAI Codex CLI | Kiro |
|---|---|---|
| Config format | markdown | markdown |
| Hierarchy support | ✓ | ✓ |
| Global config | ✓ | ✓ |
| Project config | ✓ | ✓ |
| Subdirectory scoping | ✓ | ✗ |
| File inclusion / imports | ✗ | ✗ |
| Ignore file | .codexignore | ✗ |
| IDE integration | CLI | ✓ |
| Schema / structure | Free-form (Markdown) | Free-form (Markdown) |
| Git committed | ✓ | ✓ |
| Encoding | UTF-8 | UTF-8 |
FILE MAPPING
| Purpose | OpenAI Codex CLI | Kiro |
|---|---|---|
| Project instructions | AGENTS.md | .kiro/steering/*.md |
| Project instructions | AGENTS.override.md | AGENTS.md |
| Settings / configuration | ~/.codex/config.toml | .kiro/hooks/*.kiro.hook |
SIDE-BY-SIDE CODE SAMPLES
OpenAI Codex CLI
AGENTS.md
markdown
# AGENTS.md
## Project Overview
This is a Next.js 14 e-commerce application using the App Router,
Server Components, and Drizzle ORM with PostgreSQL.
## Code Conventions
- Use TypeScript strict mode throughout
- Prefer Server Components; use "use client" only when necessary
- Name files with kebab-case: `product-card.tsx`, not `ProductCard.tsx`
- Co-locate tests: `product-card.test.tsx` next to `product-card.tsx`
## Architecture
- `app/` — Next.js App Router pages and layouts
- `components/` — Shared UI components
- `lib/` — Utilities, database client, auth helpers
- `actions/` — Server Actions for mutations
## Testing
- Use Vitest for unit tests, Playwright for E2E
- Mock database calls using `lib/test-utils.ts` helpers
- Every new component needs at least one test
## Build Commands
```bash
pnpm dev # Start dev server
pnpm build # Production build
pnpm test # Run Vitest
pnpm test:e2e # Run Playwright
pnpm lint # ESLint check
```
Kiro
.kiro/steering/*.md
markdown
---
inclusion: always
---
# Project Standards
## Stack
- TypeScript 5.x with Node.js 22
- AWS CDK v2 for infrastructure
- DynamoDB for data, S3 for assets
## Conventions
- Use ESM imports, not CommonJS
- Lambda handlers export a named `handler` function
- Use middy middleware for cross-cutting concerns
- All API responses follow JSON:API format
## Testing
- Unit tests with vitest
- Integration tests with aws-testing-library
- E2E tests use deployed staging environment
KEY DIFFERENCES
OpenAI Codex CLI: Supported. Kiro: Not supported.
OpenAI Codex CLI: .codexignore. Kiro: Not supported.
OpenAI Codex CLI: CLI. Kiro: Supported.
WHICH SHOULD I USE?
Choose based on your IDE/CLI preference. If you use OpenAI Codex CLI, configure AGENTS.md. If you use Kiro, configure .kiro/steering/*.md. Many projects include config files for multiple tools so each team member can use their preferred editor.
PORTABILITY TIP
sync-instructions.sh
bash
# Maintain a single source of truth:
cp AI-INSTRUCTIONS.md CLAUDE.md
cp AI-INSTRUCTIONS.md .cursorrules
cp AI-INSTRUCTIONS.md AGENTS.md
SEE ALSO
Tool pages:
File references:
agentconfig.ing2026-03-16COMPARE(1)