The Component
Eight structural parts — Interface, Boundary, Port, Domain, Architecture, Verification, Observability, Documentation — that repeat at every scale of software.
Fractal Co-Design
Port-first. Surface before architecture. The same structural discipline at every scale.
What is Fractal Co-Design?
Fractal Co-Design (FCD) is a software design methodology that combines two complementary ideas:
- Fractal Component Architecture (FCA) — structural. The same 8-part component model repeats from a function to a package to a system. Co-located documentation. Port-based dependency injection. Boundaries enforced by directory structure.
- Extreme Co-Design (ECD) — process. Domains identified first, shared surfaces (ports) co-designed second, internal architecture follows third — constrained by the frozen ports.
Together: every cross-domain interaction is a co-designed, frozen port. Architecture decisions follow port correctness, not the other way around.
The Levels
L0 (Function) through L5 (System). The same discipline applies at each scale, with promotion and demotion as the system grows.
Surface-First
Ports are co-designed and frozen before either side implements. The interface between components matters more than the implementation within them.
Claude Skills
The fcd-* skill family bakes FCD discipline into Claude Code: card, design, plan, surface, commission, debate, review.
The fastest path
- FCA — The Component — what an FCA component is, the 8 parts, the fractal claim.
- ECD — Extreme Co-Design — the process discipline that makes FCA tractable in teams.
- FCA — Applied Example — the methodology in action.
Status
This is the v0.1 documentation site. Canon (FCA + ECD) and the fcd-* Claude skills are stable. The @fractal-co-design/fca-index tool is migrating from @methodts/fca-index@0.4 and will land in v0.2 with rich diagram embeds via GlyphJS.