MCPInstall

role-creator

by am-will

Create and update Codex custom agents using standalone custom-agent TOML files.

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Install

Works with every agent the skills CLI supports.

npx skills add https://github.com/am-will/codex-skills --skill role-creator
  1. 01

    Install

    Run the command in your project. The CLI asks which agents to install for.

  2. 02

    Describe the task

    Ask your agent for something this skill covers. It loads role-creator automatically when relevant.

  3. 03

    Review the result

    The agent follows the SKILL.md steps, scripts and references bundled with the skill.

SKILL.md

The instructions your agent reads when the skill is triggered.

Role Creator

Overview

Use this skill to author, update, or troubleshoot custom Codex agents as standalone TOML files.

Current behavior:

  • Each custom agent is defined by one file:
    • Global: ~/.codex/agents/<agent-name>.toml
    • Project: <project>/.codex/agents/<agent-name>.toml
  • The agent file is the role source of truth.
  • ~/.codex/config.toml is only for global/runtime settings (for example [agents] thread limits), not per-role registration.

Non-Negotiable Inputs

Step 1 is required before writing files:

  • name (role identifier used by agent_type)
  • description (short, human-readable purpose)
  • developer_instructions
  • model (recommend gpt-5.3-codex unless requested)
  • model_reasoning_effort (none|minimal|low|medium|high|xhigh)
  • role scope (global or project)
  • output TOML path (canonical absolute path preferred)
  • whether to include nickname_candidates and exact values

Execution rule:

  • Do not infer required values.
  • Do not write until required inputs are explicitly confirmed.

Role file contract (current)

From Codex custom agent docs (/codex/subagents):

  • Required keys: name, description, developer_instructions.
  • Optional keys: nickname_candidates, model, model_reasoning_effort, sandbox_mode, web_search, mcp_servers, skills.config, etc.
  • name is the spawn identifier and source of truth.
  • description + developer_instructions define behavior and usage boundaries.
  • nickname_candidates is optional and used only for display.

nickname_candidates requirements:

  • Must be a non-empty list of unique values when present.
  • Allowed characters: ASCII letters, digits, spaces, hyphens, underscores.

Default policy for optional settings

  • Do not add sandboxing/MCP/web-search/model extras unless requested.
  • Keep generated files minimal by default.
  • If the user says "inherit defaults", omit optional keys instead of setting explicit values.

Workflow

  1. Collect and confirm required inputs.
  2. Resolve output path:
    • global → ~/.codex/agents/<name>.toml
    • project → <project>/.codex/agents/<name>.toml
  3. Create or update the file directly with required keys.
  4. Validate TOML parse and required keys.
  5. Return a ready-to-run example call:
{"agent_type":"<name>","message":"<task>"}

Commands

# 1) Write a standalone custom-agent file
/home/willr/Applications/skills/skills/role-creator/scripts/write_role_config.sh \
  --output ~/.codex/agents/reviewer.toml \
  --role-name reviewer \
  --description "PR reviewer focused on correctness, security, and risk." \
  --model gpt-5.4 \
  --reasoning high \
  --developer-instructions "Review code like an owner. Lead with concrete findings and residual risks."

# Optional: include nickname candidates for display
/home/willr/Applications/skills/skills/role-creator/scripts/write_role_config.sh \
  --output ~/.codex/agents/reviewer.toml \
  --role-name reviewer \
  --description "PR reviewer focused on correctness, security, and risk." \
  --model gpt-5.4 \
  --reasoning high \
  --developer-instructions "Review code like an owner. Lead with concrete findings and residual risks." \
  --nickname-candidates "Atlas,Delta,Echo" \
  --sandbox-mode read-only \
  --web-search disabled

Guardrails

  • If runtime returns unknown agent_type, verify the active scope and confirm the file exists at the expected path.
  • Check syntax first with tomlq or tomlq -C.
  • Keep role instructions operational and narrowly scoped to avoid drift.

References

  • Codex subagents docs: https://developers.openai.com/codex/subagents
  • Display nicknames: https://developers.openai.com/codex/subagents#display-nicknames
  • Reusable templates: templates/

FAQ

What does the role-creator skill do?

Create and update Codex custom agents using standalone custom-agent TOML files.

How do I install role-creator?

Run npx skills add https://github.com/am-will/codex-skills --skill role-creator in your project. The skills CLI detects the agents you use and copies the skill into the right folder. For Claude Code you can also place the skill folder at ~/.claude/skills/role-creator/ (personal) or .claude/skills/role-creator/ (project).

Which AI agents can use role-creator?

Any agent that supports the open Agent Skills format (a folder with a SKILL.md file), including Claude Code, Codex, Cursor, GitHub Copilot, Gemini CLI, Windsurf, Cline, OpenCode and more.

Is role-creator safe to install?

No partner security audit is available yet. Skills can run commands and scripts, so read the SKILL.md and any bundled files before installing.

Who maintains role-creator?

It is published by am-will in am-will/codex-skills. It has 1,152 recorded installs.

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