Templating engine

Copier over Cookiecutter, Cruft, Yeoman and GitHub template repositories

Id: 25fa2def-a118-4f60-9117-89ab50da4cf2 Type: decision Status: active Evidence: confirmed Source: ADR-001 (docs/adr/001-copier-over-cookiecutter.md) Revisit when: copier update stops being a first-class feature, or a Python-native alternative gains native template-update support

Copier renders this template. Generated projects carry a .copier-answers.yml and pull later template changes with copier update.

Reason: native update support matters most for a template that keeps evolving — adopters pull new features, CI improvements and dependency updates instead of re-applying them by hand. Conditional file inclusion via filename patterns is cleaner than hook-based approaches, the answers file makes updates reproducible, and full Jinja2 (whitespace control, raw blocks for GitHub Actions syntax) is required by the workflow templates. Copier is actively maintained and aligned with the uv/hatchling ecosystem the generated projects use. Industry trend pointed the same way: projects such as Substrate (Superlinear) migrated from Cookiecutter/Cruft to Copier, and 2026 academic literature describes Copier as a prominent evolution of Cookiecutter.

Rejected alternative: Cookiecutter — the largest ecosystem, but no native update/sync; pulling upstream changes is manual work.

Rejected alternative: Cruft — adds cruft update/cruft check on top of Cookiecutter, but as a wrapper it is limited by Cookiecutter's internals.

Rejected alternative: Yeoman — JavaScript-based, not Python-native, heavier runtime dependency.

Rejected alternative: GitHub template repositories — no variable substitution and no conditional logic.

Consequence: adopters need copier installed; the template ecosystem is smaller than Cookiecutter's; syntax differs slightly (copier.yml).