Codex Prompt Engineering

Knowledge snapshot: 2026-02-20

Purpose

Use this skill to design or review prompts for Codex/GPT coding agents with focus on:

• quality and reliability

• token efficiency

• correct tool usage

• safe autonomy

Use When

• Writing or revising system prompts for coding agents

• Debugging weak agent behavior (stalling, verbosity, bad tool calls)

• Calibrating reasoning_effort (none|low|medium|high|xhigh )

• Defining tool orchestration and planning behaviors

• Building evaluation loops for prompt iteration

Core Rules

• Calibrate reasoning effort

• none or omit for trivial formatting/retrieval

• medium default for interactive coding

• high /xhigh for complex autonomous tasks

• Run end-to-end autonomously

• gather context -> plan -> implement -> test -> refine

• ask only for ambiguity, destructive actions, or major architecture trade-offs

• Use correct tool contracts

• file edits: apply_patch

• shell execution: exec_command

• task tracking: update_plan with plan: [{step, status}]

• batch independent calls with multi_tool_use.parallel

• Keep communication compact

• tiny change: 2-5 sentences

• medium change: <=6 bullets

• large change: per-file summary + rationale

• Evaluate systematically

• Analyze -> Measure -> Improve -> Repeat

• keep graders and representative datasets

• Apply security basics

• validate/sanitize untrusted inputs

• defend against direct/indirect prompt injection

• enforce least privilege for tools/data

Runtime Mapping Note

Some environments expose shell tools under different names. In this repository runtime:

• use exec_command (not shell_command )

• use update_plan schema: plan with step/status

File Guide

• reference.md : compact canonical guidance and checklists

• patterns.md : reusable patterns beyond prompt engineering

• examples.md : concise before/after examples with correct contracts

Invocation

Use codex-prompt-engineering to review this prompt for quality and token efficiency.