Codex Skill Guide

Running a Task

Default to

gpt-5.2

model. Ask the user (via

AskUserQuestion

) which reasoning effort to use (

xhigh

,

high

,

medium

, or

low

). User can override model if needed (see Model Options below).

Select the sandbox mode required for the task; default to

--sandbox read-only

unless edits or network access are necessary.

Assemble the command with the appropriate options:

-m, --model

--config model_reasoning_effort=""

--sandbox

--full-auto

-C, --cd

--skip-git-repo-check

Always use --skip-git-repo-check.

When continuing a previous session, use

codex exec --skip-git-repo-check resume --last

via stdin. When resuming don't use any configuration flags unless explicitly requested by the user e.g. if he species the model or the reasoning effort when requesting to resume a session. Resume syntax:

echo "your prompt here" | codex exec --skip-git-repo-check resume --last 2>/dev/null

. All flags have to be inserted between exec and resume.

IMPORTANT

By default, append

2>/dev/null

to all

codex exec

commands to suppress thinking tokens (stderr). Only show stderr if the user explicitly requests to see thinking tokens or if debugging is needed.

Run the command, capture stdout/stderr (filtered as appropriate), and summarize the outcome for the user.

After Codex completes

, inform the user: "You can resume this Codex session at any time by saying 'codex resume' or asking me to continue with additional analysis or changes."

Quick Reference

Use case

Sandbox mode

Key flags

Read-only review or analysis

read-only

--sandbox read-only 2>/dev/null

Apply local edits

workspace-write

--sandbox workspace-write --full-auto 2>/dev/null

Permit network or broad access

danger-full-access

--sandbox danger-full-access --full-auto 2>/dev/null

Resume recent session

Inherited from original

echo "prompt" | codex exec --skip-git-repo-check resume --last 2>/dev/null

(no flags allowed)

Run from another directory

Match task needs

-C

plus other flags

2>/dev/null

Model Options

Model

Best for

Context window

Key features

gpt-5.2-max

Max model

Ultra-complex reasoning, deep problem analysis

400K input / 128K output

76.3% SWE-bench, adaptive reasoning, $1.25/$10.00

gpt-5.2

⭐

Flagship model

Software engineering, agentic coding workflows

400K input / 128K output

76.3% SWE-bench, adaptive reasoning, $1.25/$10.00

gpt-5.2-mini

Cost-efficient coding (4x more usage allowance)

400K input / 128K output

Near SOTA performance, $0.25/$2.00

gpt-5.1-thinking

Ultra-complex reasoning, deep problem analysis

400K input / 128K output

Adaptive thinking depth, runs 2x slower on hardest tasks

GPT-5.2 Advantages

76.3% SWE-bench (vs 72.8% GPT-5), 30% faster on average tasks, better tool handling, reduced hallucinations, improved code quality. Knowledge cutoff: September 30, 2024.

Reasoning Effort Levels

:

xhigh

- Ultra-complex tasks (deep problem analysis, complex reasoning, deep understanding of the problem)

high

- Complex tasks (refactoring, architecture, security analysis, performance optimization)

medium

- Standard tasks (refactoring, code organization, feature additions, bug fixes)

low

- Simple tasks (quick fixes, simple changes, code formatting, documentation)

Cached Input Discount

90% off ($0.125/M tokens) for repeated context, cache lasts up to 24 hours. Following Up After every codex command, immediately use AskUserQuestion to confirm next steps, collect clarifications, or decide whether to resume with codex exec resume --last . When resuming, pipe the new prompt via stdin: echo "new prompt" | codex exec resume --last 2>/dev/null . The resumed session automatically uses the same model, reasoning effort, and sandbox mode from the original session. Restate the chosen model, reasoning effort, and sandbox mode when proposing follow-up actions. Error Handling Stop and report failures whenever codex --version or a codex exec command exits non-zero; request direction before retrying. Before you use high-impact flags ( --full-auto , --sandbox danger-full-access , --skip-git-repo-check ) ask the user for permission using AskUserQuestion unless it was already given. When output includes warnings or partial results, summarize them and ask how to adjust using AskUserQuestion . CLI Version Requires Codex CLI v0.57.0 or later for GPT-5.2 model support. The CLI defaults to gpt-5.2 on macOS/Linux and gpt-5.2 on Windows. Check version: codex --version Use /model slash command within a Codex session to switch models, or configure default in ~/.codex/config.toml .