Should I use type or interface in TypeScript?

For plain object shapes they are almost interchangeable. Differences that matter:

interface

• Can be merged by redeclaration (declaration merging), useful for augmenting libraries:

interface Window { myAnalytics: Analytics }

• Extends with extends, and error messages are often clearer.
• Only describes object-like shapes (and classes can implements it).

type alias

• Can name anything: unions, intersections, tuples, primitives, mapped and conditional types.

type ID = string | number;
type Pair = [string, number];
type Status = 'idle' | 'loading' | 'error';
type Keys = keyof User;
type Readonly2<T> = { readonly [K in keyof T]: T[K] };

• Cannot be reopened; duplicate names are an error.
• Combine with &.

Quick guidance

1. Use interface for public object contracts and class shapes, particularly in libraries (users can extend it).
2. Use type for unions, tuples, utility/mapped types and function types.
3. Be consistent within a codebase; many teams simply use type everywhere, others follow "interface until you need type".

Performance

interface extends is cached by the compiler and can be faster than big intersections of type aliases in very large codebases.

Not just that

Prefer string-literal unions over enum for simple cases; they have no runtime output:

const roles = ['admin', 'editor', 'viewer'] as const;
type Role = typeof roles[number];

Pitfall: using object or {} as a type accepts almost anything. Use Record<string, unknown> for dictionaries.