Architecture Decisions

This document defines the team's default choices and the decision framework for when to deviate. Every prototype starts with these defaults. Deviations are acceptable but must be surfaced explicitly during plan mode with a clear trade-off statement.

Decision Framework

When suggesting anything during plan mode or implementation:

1. Check if there's a default — consult this document
2. If default exists, use it — do not suggest alternatives unless there's a concrete reason
3. If deviation is warranted, present it as: "The default is [X]. For this project, [Y] may be better because [reason]. The trade-off is [cost]. Which do you prefer?"
4. Never silently deviate — even if the alternative seems clearly better, surface the choice

This matters because multiple people work on these prototypes. Consistency reduces onboarding friction and context-switching cost. A "worse" but consistent choice is usually better than a "better" but unfamiliar one.

Stack Selection

Decision	Default	When to deviate
Next.js vs 11ty	Depends on project type	Next.js for interactive apps (forms, dashboards, auth). 11ty for content-driven sites (displays, timers, informational). If unclear, ask.
Runtime	Bun	Never deviate. Bun is always the runtime and package manager.
Monorepo tool	Bun workspaces	Never deviate.
Hosting	GitHub Pages (both stacks, via static export)	Deviate to Vercel only if the project needs SSR, edge functions, or specific region requirements. Default is GitHub Pages with output: "export".

UI Decisions (Next.js)

Decision	Default	When to deviate
Component library	shadcn/ui + Radix	Only if the prototype needs components shadcn doesn't offer AND Radix primitives can't compose them. Never for preference reasons.
CSS framework	Tailwind CSS 4	Never deviate in Next.js projects.
Icons	lucide-react	Only if a specific icon set is required by brand guidelines.
Toasts/notifications	sonner	Never deviate.
Charts	recharts	Deviate to d3 only if the visualization is highly custom and recharts can't handle it.
Form handling	React Hook Form + Zod	Never deviate. Never use Formik or Yup.
Theming	next-themes with CSS custom properties	Never deviate.
Animation	tailwindcss-animate	Deviate to Framer Motion only if the prototype requires complex gesture-driven or layout animations. Discuss first.
State management	React Context + Hook Form state	Deviate to Zustand only if multiple unrelated components need shared state beyond theme/auth. Never Redux.

UI Decisions (11ty)

Decision	Default	When to deviate
Templating	Nunjucks	Never deviate.
CSS framework	Tailwind CSS 4	With @tailwindcss/cli build step. Same shared theme as Next.js.
Client JS	Vanilla JavaScript	Deviate to Alpine.js or Preact only if interactivity requirements are extensive. Discuss first.
Data validation	Zod	Never deviate.

Architecture Decisions

Decision	Default	When to deviate
Component architecture	Three layers (Base UI → App components → Pages)	Never deviate.
Data pipeline	Separate package in monorepo	Only skip if the prototype has zero data transformation needs.
Validation	Zod schemas for all external data	Never deviate. Always validate.
API patterns	Next.js App Router API routes	Deviate to tRPC only if there are many type-safe endpoints between frontend and backend.
Auth	NextAuth v5 with Google OAuth	Deviate only if specific auth provider requirements exist.
Testing	bun test	Never deviate on tooling. Test coverage expectations are flexible per prototype.

Content & Structure Decisions (non-negotiable)

Decision	Default	When to deviate
About page	Every UI includes an about page	Never deviate. About page covers motivations, design principles, and how the project was built.
Data/format separation	Content data is always separate from templates and components	Never deviate. 11ty: src/_data/ = data, src/_includes/ = format. Next.js: src/content/ = data, src/components/ + src/app/ = format.
Design tokens	Shared tooling/theme.css using OKLCH @theme directive	Never deviate. Both stacks import the same theme file for visual consistency.

Anti-pattern: Never hardcode content in templates or page components. Always extract to data files.

Code Style Decisions (non-negotiable)

These never change across projects:

• 2-space indentation
• Double quotes
• No semicolons
• import type for type-only imports
• kebab-case for files
• PascalCase for components
• camelCase for functions and variables
• Design tokens over hardcoded values
• "use client" only where needed

CLAUDE.md Generation

Every new project must have CLAUDE.md files that encode these decisions for the specific project context. The root CLAUDE.md should contain:

1. Project structure overview
2. Tech stack with exact versions
3. Code style rules
4. Key commands (dev, build, lint)
5. Anti-patterns specific to the stack
6. Any project-specific deviations from defaults (with rationale)

App-level CLAUDE.md files should contain app-specific guidance (ports, env vars, deployment target, basePath handling).

Working With the Team

When multiple people are coding on a prototype:

• Defaults reduce "which library?" discussions
• CLAUDE.md files ensure every Claude Code session starts with the same context
• Deviations documented in CLAUDE.md prevent "why did we use X here?" confusion
• Plan mode is where deviations get decided, not during implementation