Use Composer with Claude Code and Codex

Composer runs coding sessions through Claude Code or Codex. Select both providers in agnostic-ai to share project instructions, a standing rule, and a reusable skill. Composer passes the project directory to the selected provider, which loads its native files.

Verified against Composer CLI 0.1.12 source. Release downloads were unavailable, so packaged runtime behavior and authenticated sessions were not tested.

Prepare the project

Install agnostic-ai. Install Composer through its official project, then install and sign in to the providers you use: Claude Code and Codex.

Work from your project root. Create agnostic-ai.yaml, or add both targets to your existing list:

targets: [claude, codex]

Keep existing provider files

Before the first sync, import any existing Claude Code or Codex configuration:

agnostic-ai import claude codex --dry-run --diff
agnostic-ai import claude codex

Review the imported .agnostic-ai/ sources against the original files and resolve differences before syncing. Skip this step in a fresh project. See how imports from several tools merge instructions.

Write the shared sources

Create the source folders:

mkdir -p .agnostic-ai/rules .agnostic-ai/skills

Add a project note to .agnostic-ai/AGNOSTIC_AI.md, keeping imported text:

When summarizing a change, name the files you inspected.

Save this rule as .agnostic-ai/rules/commit-subjects.md:

---
name: commit-subjects
description: Use the team's commit subject prefixes.
alwaysApply: true
---

Start suggested commit subjects with fix:, feat:, docs:, or chore:.

Save this skill as .agnostic-ai/skills/change-summary.md:

---
name: change-summary
description: Summarize a supplied change. Use when asked for a change summary.
---

1. State the effect a user sees.
2. Suggest a commit subject.
3. List the checks performed, or say that no checks were run.

For more fields, use the rules and skills references.

Generate and inspect

The first sync can replace imported files after you reconcile their instructions. Use --backup to keep the originals as .bak files.

agnostic-ai lint
agnostic-ai sync --plan --backup

Review the plan, then generate and check:

agnostic-ai sync --backup
agnostic-ai sync --check

Inspect the outputs for the note, rule, and skill:

Find the shared note in both CLAUDE.md and AGENTS.md. Codex's AGENTS.md also contains the rule; Claude Code gets it in .claude/rules/commit-subjects.md.

For later changes, edit .agnostic-ai/ and sync again. Home instructions and skills use global configuration. Additional settings, hooks, agents, and MCP servers keep their Claude Code or Codex mappings.

Check each provider in Composer

Run these from the project root after syncing. Each starts a new session with an explicit provider:

composer run --provider claude --permission-mode default 'Use the change-summary skill for this supplied change: a broken documentation link was fixed. Read the project instructions first. Do not edit files.'
composer run --provider codex --permission-mode default 'Use the change-summary skill for this supplied change: a broken documentation link was fixed. Read the project instructions first. Do not edit files.'

Check for a fix: or docs: subject, the skill's three steps, and the inspected filenames. Compare those paths with the generated files above. sync --check proves that files match their sources; the session check tests whether the installed provider loads and follows them.

Composer's run command defaults to Full access in 0.1.12. Its runtime permission mode can override provider configuration. Keep --permission-mode default for these checks. A noninteractive run stops if approval is required; use composer tui and review the provider and permission mode there to answer approvals.

Composer's skill catalog scans global provider skill folders and the Codex plugin cache, not project skill folders. Selecting a skill in the TUI displays a notice rather than invoking it. Ask the active provider to use the generated project skill, as above.