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Castmate — Right Model for the Right Job

Delegates a task to another AI coding CLI, or fans one prompt out to several models in parallel and synthesizes their independent opinions.

Dev & CodingAdvanced★ 881⑂ 76AI score 9/10Last updated: Nov 3, 2026

What it does

Castmate turns the agent CLIs already installed on your machine (Codex, Claude, Gemini, Amp, OpenCode, Cursor, Kiro, Antigravity) into on-demand collaborators. A bundled scripts/castmate.py handles execution while the host agent picks the cast, writes the prompt, reads the output, and synthesizes.

Three modes:

  • Delegate — hand one job to a single CLI, optionally with --write access
  • Fan-out — send the same prompt to 2–4 CLIs read-only for independent second opinions
  • Rounds — multiple passes where later rounds challenge and build on earlier findings

It distinguishes enforced read-only (the CLI's own sandbox blocks writes, shell, MCP and repo hooks) from best-effort (the model is merely asked), and warns against casting best-effort agents on code you didn't write. Runs land in ~/.config/makerskills/castmate/runs/ with a machine-readable run.json.

Who it's for

  • Developers who already use two or more agent CLIs
  • Anyone who wants architecture, migration or security decisions cross-checked rather than trusting one model
  • People who want to accumulate personal "use model X for job Y" casting rules over time

Examples

  1. "Cross-check this PR diff with two other models" → read-only fan-out, returning a synthesis of agreements, disagreements, flagged risks and blind spots
  2. "Have Codex write the database migration" → delegate with --write inside Codex's workspace sandbox, then the host reads git diff and runs tests/lint before handing it back
  3. "Hunt for security issues in this service" → rounds mode across 3 passes, keeping only findings that survived challenge

· · · Install guide · · ·

Try it now, no install

Paste this into Claude to use the skill without installing anything.

Read the instructions in this file and follow them to help me:
https://raw.githubusercontent.com/coreyhaines31/makerskills/HEAD/skills/castmate/SKILL.md

What I want: (describe your task here)

If Claude can't open the link, open it yourself and paste the contents instead.

↓ If it works for you, download the ZIP below and install it. Then it runs on its own — no pasting each time.

Install in the Claude app (no terminal)
  1. Download the ZIP with the button below.
  2. In Claude, open Settings → Capabilities and turn on 'Code execution and file creation'. (one time)
  3. Go to Customize → Skills → + → 'Upload a skill' and upload the ZIP.
↓ Download ZIP
Install in Claude Code

Let Claude do it — paste this into Claude Code

Install the skill I found on AI Skill Mart.
Copy the skills/castmate folder from the GitHub repo coreyhaines31/makerskills into my ~/.claude/skills/castmate/.
When it's done, tell me in one line what this skill can do.

Install with a command instead

git clone https://github.com/coreyhaines31/makerskills.git /tmp/makerskills && mkdir -p ~/.claude/skills && cp -r /tmp/makerskills/skills/castmate ~/.claude/skills/

⚠ This is a third-party skill. Check the source repository before installing.

  1. Open a terminal.
  2. Clone the repo: git clone https://github.com/coreyhaines31/makerskills.git /tmp/makerskills
  3. Copy the skill: mkdir -p ~/.claude/skills && cp -r /tmp/makerskills/skills/castmate ~/.claude/skills/
  4. Confirm Python 3 is available: python3 --version
  5. Install at least one other agent CLI and log in from your own terminal (login is interactive). Codex is the recommended first pick because it's the only CLI that confines --write to the working directory. Never paste an API key into chat.
  6. For Gemini CLI on a personal account, export GEMINI_API_KEY in your shell profile and restart the terminal — Google sign-in no longer works there.
  7. Restart Claude Code, then run python3 ~/.claude/skills/castmate/scripts/castmate.py list to see detected castmates.
  8. Run ... castmate.py test <name> until each replies "OK", then invoke it in chat with /castmate, "ask codex...", or "get a second opinion".
View source on GitHub ↗License: MIT