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Output Styles (Codex CLI) ​

Over the months since Codex CLI launched, OpenAI has progressively added features that give developers more control over how Codex behaves. What began with project-level guidance in AGENTS.md has expanded into explicit approvals, model switching, and configurable tools via the ~/.codex/config.toml file.

A particularly interesting development is the ability to influence output style—how Codex formats responses, what assumptions it makes, and how verbose it is—through both system-level configuration and session-level overrides. While Codex remains fundamentally a coding agent, OpenAI's documentation and the open-source repo make it clear that system prompts, AGENTS.md, and approvals can all steer the "voice" and interaction patterns of the agent.

What Output Styles Mean ​

Unlike small prompt tweaks, adjusting output style can shift Codex's default reasoning and communication patterns. This can be done in a few ways:

  • AGENTS.md rules — Define tone, verbosity, or preferred formats alongside project workflows.
  • System prompt overrides — Append or replace the base instructions at startup to change default behavior.
  • Session-level prompts — Ask Codex to adopt a certain style mid-conversation.

Approvals control what Codex can do (read only, auto, full). Output style controls how Codex communicates. Used together, you get predictable formatting plus safe execution.

Cross-Domain Applications ​

Even though Codex is optimized for coding, output style control lets you adapt it to other knowledge-heavy tasks:

  • Content strategy — Configure Codex to output only in brand-specific tone and markdown.
  • Research analysis — Force strict citation formats, summaries by section, and neutral language.
  • Business analysis — Apply structured reporting templates with precise terminology.
  • Design systems — Instruct Codex to output SVG diffs and follow component naming conventions.

Because Codex integrates file system operations, approvals, and MCP servers, these stylistic shifts can carry across both analysis and code changes, making it more versatile than a chat-only agent.

Domain Transformation ​

Start by testing one output style in your primary domain:

markdown
# AGENTS.md
## Output Style
- Always respond in numbered lists
- Keep explanations under 200 words
- End every plan with a "Risks" section

Then verify with a sanity check prompt: "What is the required format for your responses?"

If Codex reflects the rules, you've successfully imposed a new style.

Why It Matters ​

Output styles give you:

  • Cleaner domain focus — avoid context pollution from irrelevant defaults.
  • Consistency — every plan, diff, or analysis follows the same pattern.
  • Efficiency — less time editing or reformatting Codex's output.
  • Adaptability — the same tools can power different workflows with only style changes.

Sources ​

  • OpenAI announcement — Codex can be guided by AGENTS.md files.
  • AGENTS.md repository — reference and examples for agent configuration.
  • Codex CLI docs — approval modes, config, and command usage.
  • Codex repo — MCP server integrations and config.toml examples.