OpenAI Codex CLI vs KiroUpdated 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

FeatureOpenAI Codex CLIKiro
Config formatmarkdownmarkdown
Hierarchy support
Global config
Project config
Subdirectory scoping
File inclusion / imports
Ignore file.codexignore
IDE integrationCLI
Schema / structureFree-form (Markdown)Free-form (Markdown)
Git committed
EncodingUTF-8UTF-8

FILE MAPPING

PurposeOpenAI Codex CLIKiro
Project instructionsAGENTS.md.kiro/steering/*.md
Project instructionsAGENTS.override.mdAGENTS.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

1. Subdirectory scoping

OpenAI Codex CLI: Supported. Kiro: Not supported.

2. Ignore file

OpenAI Codex CLI: .codexignore. Kiro: Not supported.

3. IDE integration

OpenAI Codex CLI: CLI. Kiro: Supported.

WHICH SHOULD I USE?

Recommendation

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

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