How to Explain Existing Code with the OpenAI Codex Plugin

Yes, the Codex plugin can explain existing code by leveraging its review commands (/codex:review, /codex:adversarial-review) and custom skills architecture, even though it does not expose a dedicated "explain" command.

The openai/codex-plugin-cc repository extends Claude Code with OpenAI's Codex capabilities. While the plugin lacks a standalone "explain code" slash command, it generates detailed natural-language explanations of any repository by utilizing the same underlying review machinery that powers its code analysis features.

How the Codex Plugin Generates Code Explanations

Architecture Overview

The plugin functions as a thin wrapper around the locally-installed Codex CLI. In plugins/codex/scripts/lib/codex.mjs, the wrapper forwards slash-command payloads to the Codex binary and surfaces JSON-formatted output back to Claude Code. This architecture allows any command—including reviews—to return explanatory text about code functionality.

Review Commands as Explanation Engines

The primary entry points for code explanations are /codex:review and /codex:adversarial-review. These commands invoke Codex to analyze current uncommitted changes or branch diffs. The review output contains sentence-level descriptions of what the code does, why specific patterns are used, and potential issues, effectively serving as a comprehensive explanation.

Methods to Explain Code with the Codex Plugin

Immediate Explanations with /codex:review

Run a foreground review to get instant explanations of your current changes:

# Explain the current changes (read-only)

/codex:review

This prints a natural-language description of the examined code directly in your terminal.

Background Analysis and Result Retrieval

For large diffs or complex codebases, run the review asynchronously:

# Start a review in the background

/codex:review --background

# Check progress

/codex:status

# Retrieve the explanatory output

/codex:result

The /codex:result command displays the stored Codex response containing the detailed explanation.

Targeted Explanations via /codex:adversarial-review

Use the adversarial review command to focus on specific files or design aspects:

# Ask Codex to focus on a particular module

/codex:adversarial-review --background explain the purpose of the `state` module

This steerable approach allows you to request focused explanations of specific architecture components.

Creating Custom Explanation Skills

Because the plugin routes all commands through the codex.mjs wrapper, you can create custom skills that explicitly ask for explanations. Create a skill file at plugins/codex/skills/explain-code/SKILL.md:

Explain what the function `processChanges` does and why it uses a queue.

The wrapper forwards this prompt to the Codex CLI, which returns the explanatory text via the standard result mechanism.

Key Implementation Files

Understanding these source files helps when building custom explanation workflows:

• plugins/codex/scripts/lib/codex.mjs: Core wrapper that invokes the local Codex CLI and returns output to Claude Code.
• plugins/codex/commands/review.md: Specification for the /codex:review command that generates code explanations.
• plugins/codex/commands/adversarial-review.md: Specification for steerable reviews targeting specific explanation requests.
• plugins/codex/commands/result.md: Retrieves stored Codex output containing the actual explanations.
• README.md: Documents all slash commands and their explanation capabilities.

Summary

• The Codex plugin explains existing code through its review commands rather than a dedicated "explain" command.
• /codex:review and /codex:adversarial-review analyze code and return natural-language descriptions of functionality and design patterns.
• The codex.mjs wrapper forwards all requests to the Codex CLI, making the system extensible via custom skills.
• Use /codex:result to retrieve explanations from background reviews.
• Custom skills can be built to ask specific "explain this" questions by leveraging the underlying wrapper architecture.

Frequently Asked Questions

Does the Codex plugin have a dedicated /codex:explain command?

No. While there is no standalone /codex:explain command, the /codex:review and /codex:adversarial-review commands produce detailed natural-language explanations of code as part of their review output. You can also create custom skills that explicitly ask Codex to explain specific functions or modules.

How do I get an explanation of code that isn't in my current changes?

Use /codex:adversarial-review with a specific prompt targeting the file or module you want explained. For example, you can specify "explain the purpose of the state module" to get a focused explanation of code not necessarily in your uncommitted changes.

Can I save or reuse specific explanation prompts?

Yes. Create a custom skill in the plugins/codex/skills/ directory with a SKILL.md file containing your explanation prompt. The codex.mjs wrapper will forward this prompt to Codex just like any other command, allowing you to reuse specific explanation requests across your team.

What's the difference between foreground and background reviews for code explanation?

Foreground reviews (default /codex:review) run synchronously and display explanations immediately, suitable for smaller diffs. Background reviews (using the --background flag) run asynchronously via the Codex app-server, allowing you to check status with /codex:status and retrieve results later with /codex:result, which is ideal for large codebases or complex architectural explanations.

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