Amp vs OpenAI Codex CLIUpdated 2026-03-16

SUMMARY

Amp (CLI) uses markdown configuration while OpenAI Codex CLI (CLI) uses markdown. They differ on 1 of 11 compared features. Both tools provide AI-assisted development but take different approaches to project configuration.

FEATURE COMPARISON

FeatureAmpOpenAI 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

PurposeAmpOpenAI Codex CLI
Project instructionsAGENTS.mdAGENTS.md
Settings / configurationsettings.json~/.codex/config.toml
skills.agents/skills/*/SKILL.md.agents/skills/*/SKILL.md

SIDE-BY-SIDE CODE SAMPLES

Amp
AGENTS.md
markdown
# Agent Instructions

## Project Context
Go microservices monorepo using Bazel for builds.

## Build & Test
- Build all: bazel build //...
- Test all: bazel test //...
- Integration tests: docker compose up -d && bazel test //integration/...
- Lint: golangci-lint run ./...

## Code Conventions
- All services follow standard layout in /cmd and /internal
- Use structured logging with slog
- Error wrapping with fmt.Errorf("op: %w", err)
- See @docs/api-style-guide.md for API conventions

## Cross-Repo References
- Shared proto definitions in sourcegraph/proto
- Common Go libraries in sourcegraph/lib

## Security
- Never log sensitive data (tokens, passwords, PII)
- All external inputs must be validated
- Use parameterized queries for database access

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. Ignore file

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

WHICH SHOULD I USE?

Recommendation

Choose based on your IDE/CLI preference. If you use Amp, configure AGENTS.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

agentconfig.ing2026-03-16COMPARE(1)