Dev Tools

Spoiler: `.eslintrc.json` is dead. ESLint 10 dropped this week and the legacy config system finally went into the dirt where it belongs. Do not @ me — you've been getting deprecation warnings for two years.

The Setup

Flat config is now the only config. The benefits: real JS modules, ordered rule overrides, no more mystical `extends` cascade, and roughly 30% faster lints on a Tailwind 4 codebase because the resolver isn't crawling node_modules for shareable configs.

bun add -d eslint@10 @eslint/js typescript-eslint
# delete .eslintrc.* and create eslint.config.js
bun x eslint .

The Money Pattern

Behold a flat config that covers a TypeScript + Astro project — this is the whole file:

// eslint.config.js
import js from '@eslint/js';
import tseslint from 'typescript-eslint';
import astro from 'eslint-plugin-astro';

export default [
  js.configs.recommended,
  ...tseslint.configs.recommended,
  ...astro.configs.recommended,
  {
    rules: {
      '@typescript-eslint/no-unused-vars': ['error', { argsIgnorePattern: '^_' }],
      'no-console': ['warn', { allow: ['warn', 'error'] }],
    },
  },
  { ignores: ['dist/**', '.astro/**'] },
];

The Catch

The official migration script is still buggy on weird monorepo setups with shared `extends`. Anything with a Yarn PnP loader or a vendored `@rushstack/eslint-patch` will scream. Expect to hand-port one or two configs. Most Next.js/Astro/Vite repos take ten minutes.

The Verdict

Bite the bullet and migrate. Cursor and Claude Code both handle flat config noticeably better — they can actually read the rules array instead of guessing at a JSON tree. Faster CI, simpler config, less mental overhead. About time.