Amp vs OpenAI Codex CLIComparisonUpdated 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
| Feature | Amp | OpenAI Codex CLI |
|---|---|---|
| Config format | markdown | markdown |
| Hierarchy support | ✓ | ✓ |
| Global config | ✓ | ✓ |
| Project config | ✓ | ✓ |
| Subdirectory scoping | ✓ | ✓ |
| File inclusion / imports | ✗ | ✗ |
| Ignore file | ✗ | .codexignore |
| IDE integration | CLI | CLI |
| Schema / structure | Free-form (Markdown) | Free-form (Markdown) |
| Git committed | ✓ | ✓ |
| Encoding | UTF-8 | UTF-8 |
FILE MAPPING
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
Amp: Not supported. OpenAI Codex CLI: .codexignore.
WHICH SHOULD I USE?
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
Tool pages:
agentconfig.ing2026-03-16COMPARE(1)