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layout default
title Chapter 4: Sandbox, Approvals, and MCP Integration
nav_order 4
parent Codex CLI Tutorial

Chapter 4: Sandbox, Approvals, and MCP Integration

Welcome to Chapter 4: Sandbox, Approvals, and MCP Integration. In this part of Codex CLI Tutorial: Local Terminal Agent Workflows with OpenAI Codex, you will build an intuitive mental model first, then move into concrete implementation details and practical production tradeoffs.

This chapter shows how to expand Codex capability without losing safety controls.

Learning Goals

  • apply sandbox and approval boundaries deliberately
  • connect MCP servers through config
  • isolate risky actions by policy
  • troubleshoot integration failures quickly

Safety Strategy

  • default to constrained execution where feasible
  • require approvals for high-impact actions
  • expose only necessary MCP servers and scopes

Source References

Summary

You now have a safer model for running Codex with external integrations.

Next: Chapter 5: Prompts, Skills, and Workflow Orchestration

Depth Expansion Playbook

Source Code Walkthrough

scripts/check_blob_size.py

The from class in scripts/check_blob_size.py handles a key part of this chapter's functionality:

#!/usr/bin/env python3

from __future__ import annotations

import argparse
import os
import subprocess
import sys
from dataclasses import dataclass
from pathlib import Path


DEFAULT_MAX_BYTES = 500 * 1024


@dataclass(frozen=True)
class ChangedBlob:
    path: str
    size_bytes: int
    is_allowlisted: bool
    is_binary: bool


def run_git(*args: str) -> str:
    result = subprocess.run(
        ["git", *args],
        check=True,
        capture_output=True,
        text=True,
    )
    return result.stdout

This class is important because it defines how Codex CLI Tutorial: Local Terminal Agent Workflows with OpenAI Codex implements the patterns covered in this chapter.

scripts/check_blob_size.py

The ChangedBlob class in scripts/check_blob_size.py handles a key part of this chapter's functionality:

@dataclass(frozen=True)
class ChangedBlob:
    path: str
    size_bytes: int
    is_allowlisted: bool
    is_binary: bool


def run_git(*args: str) -> str:
    result = subprocess.run(
        ["git", *args],
        check=True,
        capture_output=True,
        text=True,
    )
    return result.stdout


def load_allowlist(path: Path) -> set[str]:
    allowlist: set[str] = set()
    for raw_line in path.read_text(encoding="utf-8").splitlines():
        line = raw_line.split("#", 1)[0].strip()
        if line:
            allowlist.add(line)
    return allowlist


def get_changed_paths(base: str, head: str) -> list[str]:
    output = run_git(
        "diff",
        "--name-only",

This class is important because it defines how Codex CLI Tutorial: Local Terminal Agent Workflows with OpenAI Codex implements the patterns covered in this chapter.

scripts/check_blob_size.py

The run_git function in scripts/check_blob_size.py handles a key part of this chapter's functionality:

def run_git(*args: str) -> str:
    result = subprocess.run(
        ["git", *args],
        check=True,
        capture_output=True,
        text=True,
    )
    return result.stdout


def load_allowlist(path: Path) -> set[str]:
    allowlist: set[str] = set()
    for raw_line in path.read_text(encoding="utf-8").splitlines():
        line = raw_line.split("#", 1)[0].strip()
        if line:
            allowlist.add(line)
    return allowlist


def get_changed_paths(base: str, head: str) -> list[str]:
    output = run_git(
        "diff",
        "--name-only",
        "--diff-filter=AM",
        "--no-renames",
        "-z",
        base,
        head,
    )
    return [path for path in output.split("\0") if path]

This function is important because it defines how Codex CLI Tutorial: Local Terminal Agent Workflows with OpenAI Codex implements the patterns covered in this chapter.

scripts/check_blob_size.py

The load_allowlist function in scripts/check_blob_size.py handles a key part of this chapter's functionality:

def load_allowlist(path: Path) -> set[str]:
    allowlist: set[str] = set()
    for raw_line in path.read_text(encoding="utf-8").splitlines():
        line = raw_line.split("#", 1)[0].strip()
        if line:
            allowlist.add(line)
    return allowlist


def get_changed_paths(base: str, head: str) -> list[str]:
    output = run_git(
        "diff",
        "--name-only",
        "--diff-filter=AM",
        "--no-renames",
        "-z",
        base,
        head,
    )
    return [path for path in output.split("\0") if path]


def is_binary_change(base: str, head: str, path: str) -> bool:
    output = run_git(
        "diff",
        "--numstat",
        "--diff-filter=AM",
        "--no-renames",
        base,
        head,

This function is important because it defines how Codex CLI Tutorial: Local Terminal Agent Workflows with OpenAI Codex implements the patterns covered in this chapter.

How These Components Connect

flowchart TD
    A[from]
    B[ChangedBlob]
    C[run_git]
    D[load_allowlist]
    E[get_changed_paths]
    A --> B
    B --> C
    C --> D
    D --> E
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