Amazon Q Developer vs OpenAI Codex CLIUpdated 2026-03-16

SUMMARY

Amazon Q Developer (CLI) uses markdown configuration while OpenAI Codex CLI (CLI) 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

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

FILE MAPPING

PurposeAmazon Q DeveloperOpenAI Codex CLI
Settings / configuration.amazonq/mcp.json~/.codex/config.toml

SIDE-BY-SIDE CODE SAMPLES

Amazon Q Developer
.amazonq/rules/*.md
markdown
# React Component Standards

## Purpose
Ensure consistent React component patterns across the frontend codebase.

## Priority
High

## Instructions
- Use functional components with TypeScript
- Define props interfaces above the component
- Use React.FC only when children are expected
- Colocate styles using CSS Modules (*.module.css)
- Extract hooks into separate files when reused
- Memoize expensive computations with useMemo
- Use React.lazy for route-level code splitting

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
```

KEY DIFFERENCES

1. Hierarchy support

Amazon Q Developer: Not supported. OpenAI Codex CLI: Supported.

2. Subdirectory scoping

Amazon Q Developer: Not supported. OpenAI Codex CLI: Supported.

3. Ignore file

Amazon Q Developer: Not supported. OpenAI Codex CLI: .codexignore.

WHICH SHOULD I USE?

Recommendation

Choose based on your IDE/CLI preference. If you use Amazon Q Developer, configure .amazonq/rules/*.md. If you use OpenAI Codex CLI, configure AGENTS.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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