ai-guardrails/max-file-lines

Why This Rule Matters

AI coding assistants tend to keep appending code to the same file rather than creating new modules. This quickly produces 500+ line files that are hard to review, test, and maintain. The result is "god files" — monolithic modules that do too many things.

This rule catches file growth early so you can split before it becomes painful.

Options

max (number, default 300) — Maximum effective lines per file.
skipBlankLines (boolean, default true) — Don't count blank lines.
skipComments (boolean, default true) — Don't count comment-only lines.

{
  "rules": {
    "ai-guardrails/max-file-lines": ["warn", { "max": 300, "skipBlankLines": true, "skipComments": true }]
  }
}

Examples

❌ Invalid — file exceeds limit

// A 400-line file with service logic, utilities, types, and constants
// all mixed together. AI tools commonly produce this pattern.
export class UserService { /* ... */ }
export function validateEmail() { /* ... */ }
export function formatPhone() { /* ... */ }
export type UserProfile = { /* ... */ };
export const ROLES = { /* ... */ };
// ...hundreds more lines

✅ Valid — properly split modules

// user.service.ts (focused, under 300 lines)
export class UserService {
  findById(id: string) { /* ... */ }
  create(data: CreateUserDto) { /* ... */ }
}

// user.validators.ts (separate module)
export function validateEmail(email: string): boolean { /* ... */ }
export function formatPhone(phone: string): string { /* ... */ }

Custom Configuration

Lower the limit for stricter teams:

["warn", { "max": 200, "skipComments": true }]

Or raise it for legacy codebases you're gradually refactoring:

["warn", { "max": 500 }]

When Not To Use This Rule

• Generated files (GraphQL codegen, Prisma, etc.) — add these to .eslintignore or the ignores array instead
• Test files that intentionally need many inline test cases
• Migration files