sellier

Scaffold a Claude Code agent harness into any project.

A harness is the system that lets an AI coding agent produce correct, high-quality code consistently. It is four things working together:

1. Guidance — CLAUDE.md and rules in .claude/rules/ that shape what the agent writes.
2. Guardrails — automated checks (lint, tests, type-checking) wrapped in commands the agent runs.
3. Flywheel — a feedback loop: review feedback updates a rule file, reloads it, and re-applies. Every review improves every future conversation.
4. Executable Workflows — agents, commands, and skills under .claude/ that turn institutional knowledge into runnable procedures.

sellier ships a generic, slim version of all four. You run it once in your project, then run a single Claude command (/saddle-up) to fill in placeholders with project specifics.

Read the blog post that inspired this tool.

Quick start

Four steps from zero to a project-aware harness:

# 1. Install
pip install sellier

# 2. Scaffold the harness into your project
cd /path/to/your/project
sellier init

Then open the project in Claude Code and run:

# 3. Customize the harness for this project
/saddle-up

# 4. Audit the codebase against the harness standards
/giddy-up

/saddle-up reads your repo (package files, build config, README, branch state) and proposes values for every [PLACEHOLDER] in the harness. You confirm or correct, and Claude rewrites the files.

/giddy-up walks the codebase looking for violations of the rules in .claude/rules/ and reports findings in a single table. It is read-only — you decide what to fix.

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What sellier init writes

CLAUDE.md
.claude/
├── settings.json
├── agents/
│   ├── ci-diagnose.md
│   ├── refactor-changes.md
│   ├── review-functional.md
│   ├── review-security.md
│   └── self-review.md
├── commands/
│   ├── giddy-up.md
│   ├── pre-commit.md
│   └── saddle-up.md
├── rules/
│   ├── commits.md
│   ├── design-principles.md
│   ├── security.md
│   └── tests.md
└── skills/
    └── implement-change/SKILL.md

CLI reference

sellier init [PATH]    # default: current directory
                       #   --force, -f   overwrite existing harness files in place
                       #   --clean       remove existing .claude/ before writing
sellier version        # print installed version
sellier --help

Alternative installs

uv tool install sellier         # if you use uv
pipx install sellier            # isolated install via pipx

Placeholder syntax

Every project-specific value in the harness is a [PLACEHOLDER] token — uppercase letters, digits, and underscores in square brackets. The /saddle-up command grep-finds and replaces them. Common placeholders:

Token	Example value
[PROJECT_NAME]	"Acme Portal"
[PROJECT_DESCRIPTION]	"Internal billing dashboard for Acme accounts"
[TECH_STACK]	"TypeScript, Next.js 15, Prisma, PostgreSQL"
[MAIN_BRANCH]	"main"
[TASK_TRACKER]	"Linear"
[CI_PROVIDER]	"GitHub Actions"
[LINT_COMMAND]	"pnpm lint"
[TEST_COMMAND]	"pnpm test"
[FRONTEND_TEST_COMMAND]	"pnpm test:ui"
[BUILD_COMMAND]	"pnpm build"

You can edit the harness afterwards. sellier writes; it does not own the files - you do.

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For developers

Stack

• Python 3.14
• uv for environments and packaging
• typer for the CLI
• pytest for tests
• hatchling as the build backend

Layout

src/sellier/
├── __init__.py          # version
├── cli.py               # typer app — init / version
├── scaffolder.py        # template traversal and copy logic
└── templates/           # the harness, shipped as package data
    ├── CLAUDE.md
    └── .claude/...
tests/
├── test_cli.py          # typer CliRunner tests
└── test_scaffolder.py   # scaffolder logic tests

The templates directory is the deliverable. cli.py and scaffolder.py are thin — most of the value is in the markdown.

Develop

uv sync              # install runtime + dev dependencies
uv run pytest        # run tests
uv run sellier init /tmp/sellier-smoke   # local smoke test

Adding a placeholder

1. Use [NEW_PLACEHOLDER] in the relevant template file.
2. Add a row to the placeholder table in this README.
3. Add an entry to the expected-placeholders list in .claude/commands/saddle-up.md so Claude knows to look for it.

Adding a rule, agent, command, or skill

Drop a new file under src/sellier/templates/.claude/{rules,agents,commands,skills}/. It will ship on the next release. Use placeholders for any project-specific text.

Tests

uv run pytest                              # all tests
uv run pytest tests/test_scaffolder.py     # one file
uv run pytest -k init                      # one keyword

The scaffolder tests assert byte-equality between the templates shipped in the package and what init writes — if you add a binary asset, the test still applies.

Release

Bump the version in pyproject.toml and src/sellier/__init__.py together in a single chore(release): commit, then:

uv build
uv publish

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License

MIT