Rules File Design - Declarative Command Permission Control

Codex Rules classify commands requested outside the sandbox by command prefix. They turn guidance such as “production builds need approval” into an executable decision boundary.

Rules compared with AGENTS.md

Area	AGENTS.md	.rules
Purpose	Explain working policy	Enforce command decisions
Format	Markdown	prefix_rule(...)
Example	State that builds need approval	Mark npm run build as prompt

Rules are experimental, so confirm the current syntax before deployment.

Create a rule

Store user rules in ~/.codex/rules/default.rules or project rules in .codex/rules/*.rules for trusted projects.

prefix_rule(
    pattern = ["npm", "run", "build"],
    decision = "prompt",
    justification = "Production builds require explicit approval",
    match = ["npm run build"],
    not_match = ["npm run dev"],
)

pattern matches an argument prefix. match and not_match document examples that should or should not match.

• allow: low-impact, repeatable inspection commands
• prompt: external writes, publishing, dependencies, or broad network access
• forbidden: destructive actions or approval bypasses

Design Command Decisions

Avoid broad rules such as allowing every git command. Prefer narrow prefixes such as git status and git diff.

Policy in This Repository

This repository treats npm run dev and npm run harness:check as routine checks, while npm run build requires explicit approval. AGENTS.md explains that policy; Rules and approval settings reinforce it.

Rules cannot validate content quality or project structure. Hooks and CI handle those checks. Next, Commands and Workflows organizes reusable execution entry points.