# When to Use Read-Only Sandbox Mode with the Codex Plugin > Discover when to use read-only sandbox mode with the Codex plugin for code analysis and review. Optimize your workflow by understanding its capabilities. - Repository: [OpenAI/codex-plugin-cc](https://github.com/openai/codex-plugin-cc) - Tags: best-practices - Published: 2026-07-14 --- **Use read-only sandbox mode when you need Codex to analyze, review, or diagnose code without modifying files, and switch to write-capable mode only when you explicitly want Codex to apply patches or generate new code.** The openai/codex-plugin-cc repository provides a ChatGPT plugin that integrates Codex into your development workflow. Understanding when to use **read-only sandbox mode** versus write-capable execution is critical for safe, effective AI-assisted coding. This guide explains the specific scenarios where sandbox mode protects your codebase while delivering valuable insights based on the actual source implementation. ## What Is Read-Only Sandbox Mode? According to the source code in [`README.md`](https://github.com/openai/codex-plugin-cc/blob/main/README.md) and [`plugins/codex/skills/codex-cli-runtime/SKILL.md`](https://github.com/openai/codex-plugin-cc/blob/main/plugins/codex/skills/codex-cli-runtime/SKILL.md), Codex operates in two distinct execution styles: **Read-only (sandbox) mode** runs Codex in an isolated environment that only inspects code. It never edits, creates, or deletes files. **Write-capable mode** grants Codex permission to modify the repository, apply patches, and generate new implementations. The plugin architecture treats read-only as the safe default for analysis tasks. The documentation in [`README.md`](https://github.com/openai/codex-plugin-cc/blob/main/README.md) explicitly states that `/codex:review` "will not perform any changes" and marks `/codex:adversarial-review` as read-only commands that "do not fix code." ## When to Use Read-Only Sandbox Mode Use **read-only sandbox mode** in the following scenarios: **Code Quality Reviews** When running `/codex:review` to analyze current changes without risking unintended edits. This command is read-only by design, guaranteeing zero file modifications while providing feedback on your code. **Adversarial and Design Critiques** For architecture discussions and challenging design decisions using `/codex:adversarial-review`. The sandbox ensures Codex only critiques trade-offs and potential bugs without applying automatic fixes. **Exploratory Diagnosis** When investigating failing tests or flaky behavior without immediate remediation. Run `/codex:rescue` without the `--write` flag to get diagnostics first, or use `/codex:review` to understand the problem before allowing modifications. **Security-Sensitive Repositories** In production environments where accidental writes could be harmful. Sandboxing isolates Codex to analysis only, preventing any code changes in critical systems. **Background CI Jobs** When executing `/codex:review --background` in continuous integration pipelines. The background job remains read-only, allowing you to monitor status or cancel without worrying about repository mutations. ## How to Invoke Read-Only vs. Write Mode The invocation method determines which mode Codex uses: **Read-Only Commands** - `/codex:review` – Analyzes changes without writing - `/codex:adversarial-review` – Provides critiques only - Any `codex` command without the `--write` flag **Write-Capable Commands** - `/codex:rescue --write` – Applies fixes and patches - Any command with explicit `--write` flag As documented in [`plugins/codex/skills/codex-cli-runtime/SKILL.md`](https://github.com/openai/codex-plugin-cc/blob/main/plugins/codex/skills/codex-cli-runtime/SKILL.md), the default behavior adds `--write` unless the user explicitly requests read-only behavior. However, review-related commands override this default to remain sandboxed. Practical examples: ```bash # Read-only review (safe default) /codex:review # Read-only adversarial critique /codex:adversarial-review "challenge the caching strategy" # Background read-only review for CI /codex:review --background # Write-capable rescue (explicit permission required) /codex:rescue --write "fix the failing test" # Read-only rescue (diagnostics only) /codex:rescue "investigate the flaky test" ``` ## Key Implementation Files The sandbox behavior is defined across several configuration files: **README.md** – Lists all slash commands and explicitly marks which are read-only, documenting that review commands "will not perform any changes." **plugins/codex/skills/codex-cli-runtime/SKILL.md** – Describes the default `--write` behavior and specifies when read-only is forced for safety. **plugins/codex/agents/codex-rescue.md** – Shows the default write-capable mode for rescue operations, with exceptions for explicit read-only requests. **plugins/codex/skills/gpt-5-4-prompting/references/codex-prompt-recipes.md** – Notes that diagnosis and fix-oriented recipes run in write mode by default unless the user explicitly asks for read-only behavior. ## Summary - **Read-only sandbox mode** is the safe default for review commands like `/codex:review` and `/codex:adversarial-review`. - Use sandbox mode whenever you need analysis, design critique, or diagnostics without file modifications. - Add `--write` explicitly only when you want Codex to apply fixes, refactor code, or generate new files. - Background jobs and CI pipelines should use read-only mode to prevent accidental repository mutations. - Review commands in [`README.md`](https://github.com/openai/codex-plugin-cc/blob/main/README.md) are hardcoded as read-only, while rescue operations default to write-capable unless the flag is omitted. ## Frequently Asked Questions ### How do I know if a Codex command will modify my files? Check whether you included the `--write` flag. According to the source code in [`plugins/codex/skills/codex-cli-runtime/SKILL.md`](https://github.com/openai/codex-plugin-cc/blob/main/plugins/codex/skills/codex-cli-runtime/SKILL.md), the default behavior adds `--write` unless explicitly overridden. However, `/codex:review` and `/codex:adversarial-review` are permanently read-only regardless of flags, as documented in [`README.md`](https://github.com/openai/codex-plugin-cc/blob/main/README.md). ### Can I switch from read-only to write mode mid-session? You cannot upgrade a running sandbox session to write mode. If you started with `/codex:review` and want Codex to apply fixes, you must issue a new command with the `--write` flag, such as `/codex:rescue --write`, to grant file modification permissions. ### Is read-only mode slower than write mode? No performance difference exists between modes. The sandbox restriction is a permission boundary, not a computational overhead. The read-only mode simply prevents the file system from receiving write operations while maintaining the same analysis speed. ### What happens if I run a rescue command without --write? Running `/codex:rescue` without the `--write` flag executes the command in **read-only sandbox mode**. As noted in [`plugins/codex/agents/codex-rescue.md`](https://github.com/openai/codex-plugin-cc/blob/main/plugins/codex/agents/codex-rescue.md), this allows Codex to diagnose issues and explain solutions without applying patches, giving you the opportunity to review the planned changes before committing to them.