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underscore-internal

Disallow @internal APIs that are not underscore-prefixed.

Targeted pattern scope​

This rule checks identifier names for declarations/signatures such as:

  • class/function/type/interface/enum declarations,
  • variable declarators,
  • class methods/properties,
  • interface method/property signatures,
  • enum members.

It reports names that do not start with _ when @internal is present in a leading comment for the node (or its export declaration wrapper).

What this rule reports​

This rule reports declarations tagged with @internal when their names do not begin with _.

The convention makes internal-only APIs visually obvious and helps prevent accidental public use.

Why this rule exists​

It enforces a consistent signal that internal-only APIs are not part of the public contract.

❌ Incorrect​

/** @internal */
export function parseSecret(): void {}
export interface Thing {
 /** @internal */
 compute(): number;
}

✅ Correct​

/** @internal */
export function _parseSecret(): void {}
export interface Thing {
 /** @internal */
 _compute(): number;
}

Behavior and migration notes​

This rule reports only and does not provide an autofix.

Migration is typically renaming internal declarations to use an underscore prefix.

Options​

This rule has no options.

Additional examples​

/** @internal */
export const token = "x";
// ❌ reported

/** @internal */
export const _token = "x";
// ✅ valid

ESLint flat config example​

import etcMisc from "eslint-plugin-etc-misc";

export default [
 {
  plugins: { "etc-misc": etcMisc },
  rules: {
   "etc-misc/underscore-internal": "error",
  },
 },
];

When not to use it​

Disable this rule if your project uses a different naming convention for internal APIs.

Package documentation​

Rule catalog ID: R102

Further reading​

Adoption resources​

  • Start at warning level in CI, then move to error after cleanup.
  • Use focused codemods/autofix batches per package or directory.