Interfaces

• Selector: interface
• Required: PascalCase
• Custom: forbids prefix I* / T* when I/T is followed by uppercase

Why This Rule

PascalCase: Consistent with all other types (classes, type aliases), making the codebase uniform.

No I* prefix: The I prefix (inherited from C# and Java) is redundant in TypeScript:

• Your editor shows the type: Hover reveals whether something is an interface, type, or class
• TypeScript is structurally typed: The distinction between interface and type is often irrelevant
• Refactoring pain: Changing from interface to type shouldn't require renaming everything
• Noise without value: IUser vs User - the prefix adds no information the type system doesn't already provide

Modern TypeScript codebases overwhelmingly reject the I prefix. It's a holdover from languages where the distinction between abstract and concrete types is more critical.

Note: Prefixes like IFrame or Identifiable are allowed because they're actual words, not type prefixes.

References:

• This TS naming convention is weird - Matt Pocock - section about I and T prefixes
• TypeScript ESLint - Naming Convention for Interfaces
• TypeScript Deep Dive - Interfaces
• Avoid the I prefix for interfaces - Mário S. Camargo - detailed explanation
• Microsoft TypeScript Coding Guidelines - explicitly avoids I prefix

✅ Good

interface UserProfile {
  // WHY: PascalCase interface with no `I` prefix
  id: string;
}

interface Identifiable {
  // WHY: A real word starting with I is allowed; it's not a type-prefix
  id: string;
}

❌ Bad

interface IUserProfile {
  // WHY: `I` prefix is redundant and discouraged
  id: string;
}

interface I_Trailing {
  // WHY: odd prefixing with underscores and I makes names noisy
  id: string;
}