Interface Rules

Rules that govern how standalone interface files are written. Every rule is enabled by the recommended config and applies to .ts / .tsx files inside a /interfaces/ folder of your project.

interface-name-pascal-case

Require interface names to use PascalCase — a leading uppercase letter followed by alphanumeric characters only.

export default interface UserData {
  id: string
}

export default interface userData {
  id: string
}

Underscores and dashes are not allowed in interface names — only alphanumeric characters, with the first character uppercase.

interface-filename-matches-name

Require interface file names to match interface names (excluding extension).

export default interface CustomerProfile {
  customerId: string
}

export default interface CustomerProfile {
  customerId: string
}

A matching file name keeps the import path and the type name in lockstep, which matters when the interface is consumed across many files.

interface-one-per-file

Require exactly one interface declaration per interface file.

export default interface ApiResult {
  success: boolean
}

export default interface BillingAddress {
  street: string
}

interface ShippingAddress {
street: string
}

If you need a second interface, move it to its own file under src/interfaces/. This keeps each type easy to find and keeps the file-name / interface-name contract enforceable.

interface-require-default-export

Require the interface in an interface file to be the default export.

export default interface InvoiceData {
  invoiceId: string
}

export interface InvoiceData {
  invoiceId: string
}

The rule also accepts the equivalent export { Name as default } form:

interface ReceiptData {
  receiptId: string
}

export { ReceiptData as default }

interface-no-i-prefix

Disallow interface names that start with an I prefix (Hungarian-style notation).

export default interface UserProfile {
  name: string
}

export default interface IUserProfile {
  name: string
}

The rule only flags names that start with a capital I followed by another uppercase letter (e.g. IUser, IUserProfile). Identifiers like index or item are not affected.