Rules and Conventions - Factory Documentation

Rules are codified standards that Droid follows every time. Unlike memories (which capture decisions and context), rules define how code should be written. This guide shows you how to organize rules effectively for individuals and teams.

Works with Factory App: These conventions work identically in both the Droid CLI and the Factory App—Droid reads the same .factory/rules/ files regardless of interface.

Rules vs Other Configuration

Type	Purpose	Example
Rules	How code should be written	”Use early returns instead of nested conditionals”
Memory	What was decided and why	”We chose Zustand because Redux was too verbose”
AGENTS.md	How to build/test/run	”Run `npm test` before completing work”
Skills	How to do specific tasks	”Steps to implement a new API endpoint”

Rules are prescriptive—they tell Droid what to do. Use them for standards that should apply consistently.

Setting Up a Rules Directory

Basic Structure

Create a .factory/rules/ directory in your project:

.factory/
└── rules/
    ├── typescript.md      # TypeScript conventions
    ├── react.md           # React patterns
    ├── testing.md         # Testing requirements
    ├── api.md             # API design rules
    └── security.md        # Security requirements

For personal rules that apply across all projects:

~/.factory/
└── rules/
    ├── style.md           # Your personal style
    └── tools.md           # Tool preferences

Referencing Rules in AGENTS.md

Add a section to your AGENTS.md:

## Coding Standards

Follow the conventions documented in `.factory/rules/`:
- **TypeScript**: `.factory/rules/typescript.md`
- **React**: `.factory/rules/react.md`
- **Testing**: `.factory/rules/testing.md`
- **API Design**: `.factory/rules/api.md`
- **Security**: `.factory/rules/security.md`

When working on a file, check the relevant rules first.

Writing Effective Rules

Rule Structure

Each rule should be:

Specific: Clear enough to follow without interpretation
Actionable: Tells what to do, not just what to avoid
Scoped: States when it applies
Justified (optional): Explains why for complex rules

Template

# [Category] Rules

## [Rule Name]
**Applies to**: [file types, contexts]
**Rule**: [specific instruction]
**Example**: [code showing correct usage]
**Rationale**: [why this matters - optional]

Example Rules Files

TypeScript Rules

Create .factory/rules/typescript.md:

# TypeScript Rules

## Type Definitions

### Use `interface` for object shapes
**Applies to**: All type definitions for objects
**Rule**: Use `interface` for object types, `type` for unions, intersections, and primitives.

```typescript
// ✅ Correct
interface User {
  id: string;
  name: string;
}

type Status = 'active' | 'inactive';
type UserWithStatus = User & { status: Status };

// ❌ Avoid
type User = {
  id: string;
  name: string;
};

Avoid `any`

Applies to: All TypeScript files Rule: Never use any. Use unknown with type guards, or define proper types.

// ✅ Correct
function processData(data: unknown): string {
  if (typeof data === 'string') {
    return data.toUpperCase();
  }
  throw new Error('Expected string');
}

// ❌ Avoid
function processData(data: any): string {
  return data.toUpperCase();
}

Function Patterns

Use early returns

Applies to: All functions with conditionals Rule: Return early for edge cases instead of nesting.

// ✅ Correct
function processUser(user: User | null): string {
  if (!user) return 'No user';
  if (!user.active) return 'User inactive';
  return `Processing ${user.name}`;
}

// ❌ Avoid
function processUser(user: User | null): string {
  if (user) {
    if (user.active) {
      return `Processing ${user.name}`;
    } else {
      return 'User inactive';
    }
  } else {
    return 'No user';
  }
}

Named exports over default

Applies to: All module exports Rule: Use named exports for better refactoring and import clarity.

// ✅ Correct
export function createUser() {}
export const USER_ROLES = ['admin', 'user'] as const;

// ❌ Avoid
export default function createUser() {}

### React Rules

Create `.factory/rules/react.md`:

```markdown
# React Rules

## Component Structure

### Functional components only
**Applies to**: All React components
**Rule**: Use functional components with hooks. Never use class components.

### Props interface naming
**Applies to**: All components with props
**Rule**: Name props interface as `{ComponentName}Props`.

```tsx
// ✅ Correct
interface UserCardProps {
  user: User;
  onSelect: (user: User) => void;
}

export function UserCard({ user, onSelect }: UserCardProps) {
  return <div onClick={() => onSelect(user)}>{user.name}</div>;
}

Component file structure

Applies to: All component files Rule: Order sections as: imports, types, component, exports.

// 1. Imports (React, external, internal, types)
import { useState } from 'react';
import { Button } from '@/components/ui';
import type { User } from '@/types';

// 2. Types
interface UserListProps {
  users: User[];
}

// 3. Component
export function UserList({ users }: UserListProps) {
  const [selected, setSelected] = useState<string | null>(null);
  
  return (
    <ul>
      {users.map(user => (
        <li key={user.id}>{user.name}</li>
      ))}
    </ul>
  );
}

State Management

Zustand for client state

Applies to: Client-side state that isn’t server data Rule: Use Zustand stores in src/stores/. One store per domain.

// src/stores/useUserStore.ts
import { create } from 'zustand';

interface UserState {
  currentUser: User | null;
  setUser: (user: User) => void;
  logout: () => void;
}

export const useUserStore = create<UserState>((set) => ({
  currentUser: null,
  setUser: (user) => set({ currentUser: user }),
  logout: () => set({ currentUser: null }),
}));

React Query for server state

Applies to: All data fetched from APIs Rule: Use React Query. Queries go in src/queries/.

// src/queries/useUsers.ts
import { useQuery } from '@tanstack/react-query';

export function useUsers() {
  return useQuery({
    queryKey: ['users'],
    queryFn: () => fetch('/api/users').then(r => r.json()),
  });
}

### Testing Rules

Create `.factory/rules/testing.md`:

```markdown
# Testing Rules

## File Organization

### Colocate test files
**Applies to**: All tests except E2E
**Rule**: Place test files next to source files.

src/ └── components/ └── UserCard/ ├── UserCard.tsx ├── UserCard.test.tsx # ✅ Colocated └── index.ts

### E2E tests in dedicated directory
**Applies to**: End-to-end tests
**Rule**: Place E2E tests in `e2e/` at project root.

## Test Structure

### Descriptive test names
**Applies to**: All test cases
**Rule**: Format as "should [action] when [condition]".

```typescript
// ✅ Correct
it('should display error message when login fails', () => {});
it('should redirect to dashboard when login succeeds', () => {});

// ❌ Avoid
it('login error', () => {});
it('works', () => {});

One assertion per test

Applies to: Unit tests Rule: Test one behavior per test case. Multiple assertions OK if testing same behavior.

// ✅ Correct - testing one behavior
it('should format user name correctly', () => {
  const result = formatUserName({ first: 'John', last: 'Doe' });
  expect(result).toBe('John Doe');
});

// ✅ Also correct - same behavior, multiple aspects
it('should return complete user object', () => {
  const user = createUser('John');
  expect(user.id).toBeDefined();
  expect(user.name).toBe('John');
  expect(user.createdAt).toBeInstanceOf(Date);
});

// ❌ Avoid - testing multiple behaviors
it('should handle user operations', () => {
  expect(createUser('John').name).toBe('John');
  expect(deleteUser('123')).toBe(true);
  expect(listUsers()).toHaveLength(0);
});

Mocking

Mock at boundaries

Applies to: All mocked dependencies Rule: Mock external APIs and services, not internal functions.

// ✅ Correct - mock external API
vi.mock('@/lib/api', () => ({
  fetchUser: vi.fn().mockResolvedValue({ id: '1', name: 'John' }),
}));

// ❌ Avoid - mock internal implementation
vi.mock('@/utils/formatName', () => ({
  formatName: vi.fn().mockReturnValue('John'),
}));

Use MSW for API mocking in integration tests

Applies to: Integration tests that need API responses Rule: Use Mock Service Worker instead of mocking fetch directly.

// ✅ Correct
import { http, HttpResponse } from 'msw';

const handlers = [
  http.get('/api/users', () => {
    return HttpResponse.json([{ id: '1', name: 'John' }]);
  }),
];

### Security Rules

Create `.factory/rules/security.md`:

```markdown
# Security Rules

## Secrets Management

### Never hardcode secrets
**Applies to**: All code
**Rule**: Use environment variables for all secrets. Never commit secrets.

```typescript
// ✅ Correct
const apiKey = process.env.API_KEY;

// ❌ Never do this
const apiKey = 'sk-1234567890abcdef';

Validate environment variables

Applies to: Application startup Rule: Validate required env vars exist at startup.

// ✅ Correct
const config = {
  apiKey: requireEnv('API_KEY'),
  dbUrl: requireEnv('DATABASE_URL'),
};

function requireEnv(name: string): string {
  const value = process.env[name];
  if (!value) throw new Error(`Missing required env var: ${name}`);
  return value;
}

Input Validation

Validate all external input

Applies to: API routes, form handlers Rule: Use Zod to validate all input from users or external sources.

// ✅ Correct
import { z } from 'zod';

const CreateUserSchema = z.object({
  email: z.string().email(),
  name: z.string().min(1).max(100),
});

export async function createUser(input: unknown) {
  const data = CreateUserSchema.parse(input);
  // data is now typed and validated
}

Error Handling

Never expose internal errors

Applies to: API error responses Rule: Log detailed errors server-side; return generic messages to clients.

// ✅ Correct
try {
  await processPayment(data);
} catch (error) {
  console.error('Payment failed:', error); // Detailed log
  throw new ApiError('Payment processing failed', 500); // Generic message
}

Authentication

Check authentication on every protected route

Applies to: All API routes requiring auth Rule: Use middleware or guards. Never assume auth from client.

// ✅ Correct
export async function GET(request: Request) {
  const session = await getSession(request);
  if (!session) {
    return new Response('Unauthorized', { status: 401 });
  }
  // ... handle authenticated request
}

---

## Organizing Team Rules

### Layered Rules

For teams, organize rules in layers:

.factory/rules/ ├── _base/ # Foundation rules (everyone follows) │ ├── typescript.md │ └── security.md ├── frontend/ # Frontend-specific │ ├── react.md │ └── styling.md ├── backend/ # Backend-specific │ ├── api.md │ └── database.md └── testing/ # Testing standards ├── unit.md └── integration.md

Reference in AGENTS.md:

```markdown
## Rules
- Base rules: `.factory/rules/_base/` - Apply to all code
- Frontend rules: `.factory/rules/frontend/` - React components
- Backend rules: `.factory/rules/backend/` - API and services
- Testing rules: `.factory/rules/testing/` - All tests

Rule Ownership

Add ownership to track who maintains each rule set:

# TypeScript Rules

**Owner**: Platform Team
**Last Updated**: 2024-02-15
**Review Cycle**: Quarterly

[rules content...]

Current Limitation: No Glob Pattern Support

Currently, Droid doesn’t support conditional rule application based on file patterns (e.g., “apply these rules only to *.tsx files”). This is on the roadmap.

Workarounds:

Organize by file type: Create separate rules files and reference them contextually

# In AGENTS.md
When working on React components (*.tsx), follow `.factory/rules/react.md`
When working on API routes, follow `.factory/rules/api.md`

Use clear scoping in rules: State applicability clearly

## This rule applies to: React component files (*.tsx)

Use skills for complex workflows: Skills can encode file-type-specific instructions

Rules Maintenance

Adding New Rules

When you find yourself correcting Droid repeatedly:

Identify the pattern
Write a clear rule with examples
Add to appropriate rules file
Update AGENTS.md if needed
Test by asking Droid to do similar work

Reviewing Rules

Quarterly review checklist:

Remove rules that are now enforced by linting
Update rules that have changed
Add rules for new patterns
Check that examples are still accurate
Verify AGENTS.md references are current

Deprecating Rules

When a rule becomes outdated:

## ~~Use PropTypes for type checking~~ (DEPRECATED)
**Status**: Deprecated as of 2024-02
**Reason**: We now use TypeScript for all type checking
**Replacement**: See TypeScript rules for prop typing

Enforcing Rules Automatically

While Droid follows rules from your .factory/rules/ files, you can add automated enforcement with hooks.

Run Linters After Edits

Add a PostToolUse hook to run your linter after every file edit:

{
  "hooks": {
    "PostToolUse": [
      {
        "matcher": "Create|Edit|ApplyPatch",
        "hooks": [
          {
            "type": "command",
            "command": "cd \"$FACTORY_PROJECT_DIR\" && npm run lint -- --fix 2>/dev/null || true"
          }
        ]
      }
    ]
  }
}

Validate Code Style

Run Prettier or your formatter automatically:

{
  "hooks": {
    "PostToolUse": [
      {
        "matcher": "Create|Edit|ApplyPatch",
        "hooks": [
          {
            "type": "command",
            "command": "cd \"$FACTORY_PROJECT_DIR\" && npx prettier --write \"$(jq -r '.tool_input.file_path')\" 2>/dev/null || true"
          }
        ]
      }
    ]
  }
}

See Hooks reference for more examples.

Quick Reference

File Locations

Scope	Location	Use For
Personal	`~/.factory/rules/`	Your style preferences
Project	`.factory/rules/`	Team standards

Rule Format

## [Rule Name]
**Applies to**: [scope]
**Rule**: [what to do]
**Example**: [code]
**Rationale**: [why - optional]

Good Rules Are

✅ Specific and unambiguous
✅ Include code examples
✅ State when they apply
✅ Actionable (do X, not “consider X”)
❌ Not vague (“write clean code”)
❌ Not duplicating linter rules
❌ Not contradicting other rules

​Rules vs Other Configuration

​Setting Up a Rules Directory

​Basic Structure

​Referencing Rules in AGENTS.md

​Writing Effective Rules

​Rule Structure

​Template

​Example Rules Files

​TypeScript Rules

​Avoid any

​Function Patterns

​Use early returns

​Named exports over default

​Component file structure

​State Management

​Zustand for client state

​React Query for server state

​One assertion per test

​Mocking

​Mock at boundaries

​Use MSW for API mocking in integration tests

​Validate environment variables

​Input Validation

​Validate all external input

​Error Handling

​Never expose internal errors

​Authentication

​Check authentication on every protected route

​Rule Ownership

​Current Limitation: No Glob Pattern Support

​Rules Maintenance

​Adding New Rules

​Reviewing Rules

​Deprecating Rules

​Enforcing Rules Automatically

​Run Linters After Edits

​Validate Code Style

​Quick Reference

​File Locations

​Rule Format

​Good Rules Are

​Next Steps

Setup Checklist

Memory Management

Rules vs Other Configuration

Setting Up a Rules Directory

Basic Structure

Referencing Rules in AGENTS.md

Writing Effective Rules

Rule Structure

Template

Example Rules Files

TypeScript Rules

Avoid `any`

Function Patterns

Use early returns

Named exports over default

Component file structure

State Management

Zustand for client state

React Query for server state

One assertion per test

Mocking

Mock at boundaries

Use MSW for API mocking in integration tests

Validate environment variables

Input Validation

Validate all external input

Error Handling

Never expose internal errors

Authentication

Check authentication on every protected route

Rule Ownership

Current Limitation: No Glob Pattern Support

Rules Maintenance

Adding New Rules

Reviewing Rules

Deprecating Rules

Enforcing Rules Automatically

Run Linters After Edits

Validate Code Style

Quick Reference

File Locations

Rule Format

Good Rules Are

Next Steps