eslint-plugin-repo-lint

Add project-specific ESLint rules to a .lints/ folder. No build step, no plugin scaffolding. Great for cases ast-grep can't express.

Install

pnpm install --save-dev eslint-plugin-repo-lint

If you're writing rules in TypeScript, also install @typescript-eslint/utils:

pnpm install --save-dev @typescript-eslint/utils

Use

Flat config (ESLint 9+):

// eslint.config.js
const repoLint = require("eslint-plugin-repo-lint");

module.exports = [repoLint.configs["flat/all"]];

Or eslint.config.mjs:

import repoLint from "eslint-plugin-repo-lint";

export default [repoLint.configs["flat/all"]];

Opt in per rule instead of flat/all:

module.exports = [
  {
    plugins: { "repo-lint": require("eslint-plugin-repo-lint") },
    rules: {
      // requirement: you have a `.lints/sentry-tags-snake-case.{js,ts}` file
      "repo-lint/sentry-tags-snake-case": "error",
    },
  },
];

Legacy eslintrc (ESLint 8):

# .eslintrc.yml
extends: ["plugin:repo-lint/all"]

Write a rule

Drop a TypeScript file in .lints/. The filename becomes the rule name.

// .lints/sentry-tags-snake-case.ts
import type { TSESLint, TSESTree } from "@typescript-eslint/utils";

const rule: TSESLint.RuleModule<"snakeCase", []> = {
  meta: {
    type: "problem",
    fixable: "code",
    schema: [],
    messages: {
      snakeCase: "Tag '{{key}}' should be snake_case (suggested: '{{fixed}}').",
    },
  },
  defaultOptions: [],
  create(context) {
    return {
      CallExpression(node: TSESTree.CallExpression) {
        // ...rule logic...
      },
    };
  },
};

export default rule;

.lints/sentry-tags-snake-case.ts → repo-lint/sentry-tags-snake-case.

Plain JS files (.js) work too — they skip the transpile step.

Test a rule

Co-locate the test as <rule>.test.ts next to the rule. The loader ignores .test. and .spec. files, so it won't try to register the test as a rule.

// vitest.config.ts
import { defineConfig } from "vitest/config";

export default defineConfig({
  test: { globals: true },
});

// .lints/sentry-tags-snake-case.test.ts
import { RuleTester } from "@typescript-eslint/rule-tester";

import rule from "./sentry-tags-snake-case";

new RuleTester().run("sentry-tags-snake-case", rule, {
  valid: ["Sentry.setTag('user_id', '42');"],
  invalid: [
    {
      code: "Sentry.setTag('userId', '42');",
      errors: [{ messageId: "snakeCase" }],
    },
  ],
});

Run:

pnpx vitest run .lints

Notes

1. ESLint editor extensions typically cache loaded plugin modules. After adding or editing a rule, you might need to restart the ESLint server for your updated rule to get picked up by your editor.
2. Rules written in TypeScript are not type-checked. Run tsc --noEmit against your .lints/ folder separately if you want to check types.
3. The rule loader anchors on the first eslint.config.* (flat config) or .eslintrc.* with root: true it finds walking up from ESLint's working directory. The walk-up logic stops when it encounters a .git directory to try prevent breaking out of a repo boundary.