diff --git a/eslint-remote-tester.config.ts b/eslint-remote-tester.config.ts
index a22f38c0..d9a4f0a9 100644
--- a/eslint-remote-tester.config.ts
+++ b/eslint-remote-tester.config.ts
@@ -1,8 +1,7 @@
 import tsparser from '@typescript-eslint/parser';
 import type { Config } from 'eslint-remote-tester';
 
-// @ts-expect-error - eslint-plugin is not typed yet
-import eslintPlugin from './lib/index.js';
+import eslintPlugin from './lib/index.ts';
 
 export default {
   /** Repositories to scan */
diff --git a/eslint.config.ts b/eslint.config.ts
index 8a7fb34e..7f7b02b8 100644
--- a/eslint.config.ts
+++ b/eslint.config.ts
@@ -7,7 +7,7 @@ import markdown from 'eslint-plugin-markdown';
 import pluginN from 'eslint-plugin-n';
 import tseslint from 'typescript-eslint';
 
-import eslintPlugin from './lib/index.js';
+import eslintPlugin from './lib/index.ts';
 
 const dirname = path.dirname(fileURLToPath(import.meta.url));
 const compat = new FlatCompat({
diff --git a/lib/index.ts b/lib/index.ts
index 89ea9f0c..4d99210f 100644
--- a/lib/index.ts
+++ b/lib/index.ts
@@ -6,38 +6,38 @@ import { createRequire } from 'node:module';
 
 import type { ESLint, Linter, Rule } from 'eslint';
 
-import consistentOutput from './rules/consistent-output.js';
-import fixerReturn from './rules/fixer-return.js';
-import metaPropertyOrdering from './rules/meta-property-ordering.js';
-import noDeprecatedContextMethods from './rules/no-deprecated-context-methods.js';
-import noDeprecatedReportApi from './rules/no-deprecated-report-api.js';
-import noIdenticalTests from './rules/no-identical-tests.js';
-import noMetaReplacedBy from './rules/no-meta-replaced-by.js';
-import noMetaSchemaDefault from './rules/no-meta-schema-default.js';
-import noMissingMessageIds from './rules/no-missing-message-ids.js';
-import noMissingPlaceholders from './rules/no-missing-placeholders.js';
-import noOnlyTests from './rules/no-only-tests.js';
-import noPropertyInNode from './rules/no-property-in-node.js';
-import noUnusedMessageIds from './rules/no-unused-message-ids.js';
-import noUnusedPlaceholders from './rules/no-unused-placeholders.js';
-import noUselessTokenRange from './rules/no-useless-token-range.js';
-import preferMessageIds from './rules/prefer-message-ids.js';
-import preferObjectRule from './rules/prefer-object-rule.js';
-import preferOutputNull from './rules/prefer-output-null.js';
-import preferPlaceholders from './rules/prefer-placeholders.js';
-import preferReplaceText from './rules/prefer-replace-text.js';
-import reportMessageFormat from './rules/report-message-format.js';
-import requireMetaDefaultOptions from './rules/require-meta-default-options.js';
-import requireMetaDocsDescription from './rules/require-meta-docs-description.js';
-import requireMetaDocsRecommended from './rules/require-meta-docs-recommended.js';
-import requireMetaDocsUrl from './rules/require-meta-docs-url.js';
-import requireMetaFixable from './rules/require-meta-fixable.js';
-import requireMetaHasSuggestions from './rules/require-meta-has-suggestions.js';
-import requireMetaSchemaDescription from './rules/require-meta-schema-description.js';
-import requireMetaSchema from './rules/require-meta-schema.js';
-import requireMetaType from './rules/require-meta-type.js';
-import testCasePropertyOrdering from './rules/test-case-property-ordering.js';
-import testCaseShorthandStrings from './rules/test-case-shorthand-strings.js';
+import consistentOutput from './rules/consistent-output.ts';
+import fixerReturn from './rules/fixer-return.ts';
+import metaPropertyOrdering from './rules/meta-property-ordering.ts';
+import noDeprecatedContextMethods from './rules/no-deprecated-context-methods.ts';
+import noDeprecatedReportApi from './rules/no-deprecated-report-api.ts';
+import noIdenticalTests from './rules/no-identical-tests.ts';
+import noMetaReplacedBy from './rules/no-meta-replaced-by.ts';
+import noMetaSchemaDefault from './rules/no-meta-schema-default.ts';
+import noMissingMessageIds from './rules/no-missing-message-ids.ts';
+import noMissingPlaceholders from './rules/no-missing-placeholders.ts';
+import noOnlyTests from './rules/no-only-tests.ts';
+import noPropertyInNode from './rules/no-property-in-node.ts';
+import noUnusedMessageIds from './rules/no-unused-message-ids.ts';
+import noUnusedPlaceholders from './rules/no-unused-placeholders.ts';
+import noUselessTokenRange from './rules/no-useless-token-range.ts';
+import preferMessageIds from './rules/prefer-message-ids.ts';
+import preferObjectRule from './rules/prefer-object-rule.ts';
+import preferOutputNull from './rules/prefer-output-null.ts';
+import preferPlaceholders from './rules/prefer-placeholders.ts';
+import preferReplaceText from './rules/prefer-replace-text.ts';
+import reportMessageFormat from './rules/report-message-format.ts';
+import requireMetaDefaultOptions from './rules/require-meta-default-options.ts';
+import requireMetaDocsDescription from './rules/require-meta-docs-description.ts';
+import requireMetaDocsRecommended from './rules/require-meta-docs-recommended.ts';
+import requireMetaDocsUrl from './rules/require-meta-docs-url.ts';
+import requireMetaFixable from './rules/require-meta-fixable.ts';
+import requireMetaHasSuggestions from './rules/require-meta-has-suggestions.ts';
+import requireMetaSchemaDescription from './rules/require-meta-schema-description.ts';
+import requireMetaSchema from './rules/require-meta-schema.ts';
+import requireMetaType from './rules/require-meta-type.ts';
+import testCasePropertyOrdering from './rules/test-case-property-ordering.ts';
+import testCaseShorthandStrings from './rules/test-case-shorthand-strings.ts';
 
 const require = createRequire(import.meta.url);
 
diff --git a/lib/rules/consistent-output.ts b/lib/rules/consistent-output.ts
index 6495fec3..82e0fcf3 100644
--- a/lib/rules/consistent-output.ts
+++ b/lib/rules/consistent-output.ts
@@ -4,7 +4,7 @@
  */
 import type { Rule } from 'eslint';
 
-import { getKeyName, getTestInfo } from '../utils.js';
+import { getKeyName, getTestInfo } from '../utils.ts';
 
 const keyNameMapper = (property: Parameters<typeof getKeyName>[0]) =>
   getKeyName(property);
diff --git a/lib/rules/fixer-return.ts b/lib/rules/fixer-return.ts
index 97aedf04..6b71abda 100644
--- a/lib/rules/fixer-return.ts
+++ b/lib/rules/fixer-return.ts
@@ -17,8 +17,8 @@ import {
   getContextIdentifiers,
   isAutoFixerFunction,
   isSuggestionFixerFunction,
-} from '../utils.js';
-import type { FunctionInfo } from '../types.js';
+} from '../utils.ts';
+import type { FunctionInfo } from '../types.ts';
 
 const DEFAULT_FUNC_INFO: FunctionInfo = {
   upper: null,
diff --git a/lib/rules/meta-property-ordering.ts b/lib/rules/meta-property-ordering.ts
index 88125d70..c4ad2019 100644
--- a/lib/rules/meta-property-ordering.ts
+++ b/lib/rules/meta-property-ordering.ts
@@ -3,7 +3,7 @@
  */
 import type { Rule } from 'eslint';
 
-import { getKeyName, getRuleInfo } from '../utils.js';
+import { getKeyName, getRuleInfo } from '../utils.ts';
 
 const defaultOrder = [
   'type',
diff --git a/lib/rules/no-deprecated-context-methods.ts b/lib/rules/no-deprecated-context-methods.ts
index bd2a126f..91d82bf1 100644
--- a/lib/rules/no-deprecated-context-methods.ts
+++ b/lib/rules/no-deprecated-context-methods.ts
@@ -5,7 +5,7 @@
 import type { Rule } from 'eslint';
 import type { Identifier, MemberExpression } from 'estree';
 
-import { getContextIdentifiers } from '../utils.js';
+import { getContextIdentifiers } from '../utils.ts';
 
 const DEPRECATED_PASSTHROUGHS = {
   getSource: 'getText',
diff --git a/lib/rules/no-deprecated-report-api.ts b/lib/rules/no-deprecated-report-api.ts
index 91a3b622..3c4bb955 100644
--- a/lib/rules/no-deprecated-report-api.ts
+++ b/lib/rules/no-deprecated-report-api.ts
@@ -5,7 +5,7 @@
 import type { Rule } from 'eslint';
 import type { Node } from 'estree';
 
-import { getContextIdentifiers, getReportInfo } from '../utils.js';
+import { getContextIdentifiers, getReportInfo } from '../utils.ts';
 
 // ------------------------------------------------------------------------------
 // Rule Definition
diff --git a/lib/rules/no-identical-tests.ts b/lib/rules/no-identical-tests.ts
index d60b5a48..8454877c 100644
--- a/lib/rules/no-identical-tests.ts
+++ b/lib/rules/no-identical-tests.ts
@@ -5,7 +5,7 @@
 import type { Rule } from 'eslint';
 import type { Expression, SpreadElement } from 'estree';
 
-import { getTestInfo } from '../utils.js';
+import { getTestInfo } from '../utils.ts';
 
 // ------------------------------------------------------------------------------
 // Rule Definition
diff --git a/lib/rules/no-meta-replaced-by.ts b/lib/rules/no-meta-replaced-by.ts
index c126a225..8bf3000a 100644
--- a/lib/rules/no-meta-replaced-by.ts
+++ b/lib/rules/no-meta-replaced-by.ts
@@ -3,7 +3,7 @@
  */
 import type { Rule } from 'eslint';
 
-import { evaluateObjectProperties, getKeyName, getRuleInfo } from '../utils.js';
+import { evaluateObjectProperties, getKeyName, getRuleInfo } from '../utils.ts';
 
 // ------------------------------------------------------------------------------
 // Rule Definition
diff --git a/lib/rules/no-meta-schema-default.ts b/lib/rules/no-meta-schema-default.ts
index db9905d8..4bd8273f 100644
--- a/lib/rules/no-meta-schema-default.ts
+++ b/lib/rules/no-meta-schema-default.ts
@@ -6,7 +6,7 @@ import {
   getMetaSchemaNode,
   getMetaSchemaNodeProperty,
   getRuleInfo,
-} from '../utils.js';
+} from '../utils.ts';
 
 // ------------------------------------------------------------------------------
 // Rule Definition
diff --git a/lib/rules/no-missing-message-ids.ts b/lib/rules/no-missing-message-ids.ts
index 74c594cb..6e84808a 100644
--- a/lib/rules/no-missing-message-ids.ts
+++ b/lib/rules/no-missing-message-ids.ts
@@ -9,7 +9,7 @@ import {
   getMessagesNode,
   getReportInfo,
   getRuleInfo,
-} from '../utils.js';
+} from '../utils.ts';
 
 // ------------------------------------------------------------------------------
 // Rule Definition
diff --git a/lib/rules/no-missing-placeholders.ts b/lib/rules/no-missing-placeholders.ts
index d6047320..b0b0b872 100644
--- a/lib/rules/no-missing-placeholders.ts
+++ b/lib/rules/no-missing-placeholders.ts
@@ -14,7 +14,7 @@ import {
   getMessagesNode,
   getReportInfo,
   getRuleInfo,
-} from '../utils.js';
+} from '../utils.ts';
 
 // ------------------------------------------------------------------------------
 // Rule Definition
diff --git a/lib/rules/no-only-tests.ts b/lib/rules/no-only-tests.ts
index 2a59cc3d..0ad0dbc3 100644
--- a/lib/rules/no-only-tests.ts
+++ b/lib/rules/no-only-tests.ts
@@ -5,7 +5,7 @@ import {
 } from '@eslint-community/eslint-utils';
 import type { Rule } from 'eslint';
 
-import { getTestInfo } from '../utils.js';
+import { getTestInfo } from '../utils.ts';
 
 const rule: Rule.RuleModule = {
   meta: {
diff --git a/lib/rules/no-unused-message-ids.ts b/lib/rules/no-unused-message-ids.ts
index 601daa3b..8f8b2eb0 100644
--- a/lib/rules/no-unused-message-ids.ts
+++ b/lib/rules/no-unused-message-ids.ts
@@ -10,7 +10,7 @@ import {
   getReportInfo,
   getRuleInfo,
   isVariableFromParameter,
-} from '../utils.js';
+} from '../utils.ts';
 
 // ------------------------------------------------------------------------------
 // Rule Definition
diff --git a/lib/rules/no-unused-placeholders.ts b/lib/rules/no-unused-placeholders.ts
index cee772c7..cb12058a 100644
--- a/lib/rules/no-unused-placeholders.ts
+++ b/lib/rules/no-unused-placeholders.ts
@@ -14,7 +14,7 @@ import {
   getMessagesNode,
   getReportInfo,
   getRuleInfo,
-} from '../utils.js';
+} from '../utils.ts';
 
 // ------------------------------------------------------------------------------
 // Rule Definition
diff --git a/lib/rules/no-useless-token-range.ts b/lib/rules/no-useless-token-range.ts
index a17e516b..e41c6716 100644
--- a/lib/rules/no-useless-token-range.ts
+++ b/lib/rules/no-useless-token-range.ts
@@ -5,7 +5,7 @@
 import type { Rule } from 'eslint';
 import type { Expression, MemberExpression, SpreadElement } from 'estree';
 
-import { getKeyName, getSourceCodeIdentifiers } from '../utils.js';
+import { getKeyName, getSourceCodeIdentifiers } from '../utils.ts';
 
 // ------------------------------------------------------------------------------
 // Rule Definition
diff --git a/lib/rules/prefer-message-ids.ts b/lib/rules/prefer-message-ids.ts
index 1d1ccedb..1ef3b88d 100644
--- a/lib/rules/prefer-message-ids.ts
+++ b/lib/rules/prefer-message-ids.ts
@@ -8,7 +8,7 @@ import {
   getKeyName,
   getReportInfo,
   getRuleInfo,
-} from '../utils.js';
+} from '../utils.ts';
 
 // ------------------------------------------------------------------------------
 // Rule Definition
diff --git a/lib/rules/prefer-object-rule.ts b/lib/rules/prefer-object-rule.ts
index d07d7cf2..f904a6c6 100644
--- a/lib/rules/prefer-object-rule.ts
+++ b/lib/rules/prefer-object-rule.ts
@@ -3,7 +3,7 @@
  */
 import type { Rule } from 'eslint';
 
-import { getRuleInfo } from '../utils.js';
+import { getRuleInfo } from '../utils.ts';
 
 // ------------------------------------------------------------------------------
 // Rule Definition
diff --git a/lib/rules/prefer-output-null.ts b/lib/rules/prefer-output-null.ts
index 1b2cc8f6..57e50e2f 100644
--- a/lib/rules/prefer-output-null.ts
+++ b/lib/rules/prefer-output-null.ts
@@ -6,7 +6,7 @@
 import type { Rule } from 'eslint';
 import type { Property } from 'estree';
 
-import { getTestInfo } from '../utils.js';
+import { getTestInfo } from '../utils.ts';
 
 // ------------------------------------------------------------------------------
 // Rule Definition
diff --git a/lib/rules/prefer-placeholders.ts b/lib/rules/prefer-placeholders.ts
index d8a9d217..e2026787 100644
--- a/lib/rules/prefer-placeholders.ts
+++ b/lib/rules/prefer-placeholders.ts
@@ -11,7 +11,7 @@ import {
   collectReportViolationAndSuggestionData,
   getContextIdentifiers,
   getReportInfo,
-} from '../utils.js';
+} from '../utils.ts';
 
 // ------------------------------------------------------------------------------
 // Rule Definition
diff --git a/lib/rules/prefer-replace-text.ts b/lib/rules/prefer-replace-text.ts
index 1a96d65e..1b2ac928 100644
--- a/lib/rules/prefer-replace-text.ts
+++ b/lib/rules/prefer-replace-text.ts
@@ -5,12 +5,12 @@
 import type { Rule } from 'eslint';
 import type { Identifier, Node } from 'estree';
 
-import type { FunctionInfo } from '../types.js';
+import type { FunctionInfo } from '../types.ts';
 import {
   getContextIdentifiers,
   isAutoFixerFunction,
   isSuggestionFixerFunction,
-} from '../utils.js';
+} from '../utils.ts';
 
 const DEFAULT_FUNC_INFO: FunctionInfo = {
   upper: null,
diff --git a/lib/rules/report-message-format.ts b/lib/rules/report-message-format.ts
index 4ba7506d..9ac571b6 100644
--- a/lib/rules/report-message-format.ts
+++ b/lib/rules/report-message-format.ts
@@ -11,7 +11,7 @@ import {
   getKeyName,
   getReportInfo,
   getRuleInfo,
-} from '../utils.js';
+} from '../utils.ts';
 
 // ------------------------------------------------------------------------------
 // Rule Definition
diff --git a/lib/rules/require-meta-default-options.ts b/lib/rules/require-meta-default-options.ts
index ac836c4a..608c5742 100644
--- a/lib/rules/require-meta-default-options.ts
+++ b/lib/rules/require-meta-default-options.ts
@@ -6,7 +6,7 @@ import {
   getMetaSchemaNode,
   getMetaSchemaNodeProperty,
   getRuleInfo,
-} from '../utils.js';
+} from '../utils.ts';
 
 const rule: Rule.RuleModule = {
   meta: {
diff --git a/lib/rules/require-meta-docs-description.ts b/lib/rules/require-meta-docs-description.ts
index dd0af4eb..d2b9c6aa 100644
--- a/lib/rules/require-meta-docs-description.ts
+++ b/lib/rules/require-meta-docs-description.ts
@@ -1,7 +1,7 @@
 import { getStaticValue } from '@eslint-community/eslint-utils';
 import type { Rule } from 'eslint';
 
-import { getMetaDocsProperty, getRuleInfo } from '../utils.js';
+import { getMetaDocsProperty, getRuleInfo } from '../utils.ts';
 
 const DEFAULT_PATTERN = new RegExp('^(enforce|require|disallow)');
 
diff --git a/lib/rules/require-meta-docs-recommended.ts b/lib/rules/require-meta-docs-recommended.ts
index ae3f7d8e..f37bd0e9 100644
--- a/lib/rules/require-meta-docs-recommended.ts
+++ b/lib/rules/require-meta-docs-recommended.ts
@@ -6,7 +6,7 @@ import {
   getMetaDocsProperty,
   getRuleInfo,
   isUndefinedIdentifier,
-} from '../utils.js';
+} from '../utils.ts';
 
 function insertRecommendedProperty(
   fixer: Rule.RuleFixer,
diff --git a/lib/rules/require-meta-docs-url.ts b/lib/rules/require-meta-docs-url.ts
index 4a94764e..699aca64 100644
--- a/lib/rules/require-meta-docs-url.ts
+++ b/lib/rules/require-meta-docs-url.ts
@@ -11,7 +11,7 @@ import {
   getRuleInfo,
   insertProperty,
   isUndefinedIdentifier,
-} from '../utils.js';
+} from '../utils.ts';
 
 // -----------------------------------------------------------------------------
 // Rule Definition
diff --git a/lib/rules/require-meta-fixable.ts b/lib/rules/require-meta-fixable.ts
index d3d23bf7..785c3694 100644
--- a/lib/rules/require-meta-fixable.ts
+++ b/lib/rules/require-meta-fixable.ts
@@ -11,7 +11,7 @@ import {
   getContextIdentifiers,
   getKeyName,
   getRuleInfo,
-} from '../utils.js';
+} from '../utils.ts';
 
 // ------------------------------------------------------------------------------
 // Rule Definition
diff --git a/lib/rules/require-meta-has-suggestions.ts b/lib/rules/require-meta-has-suggestions.ts
index c031bfcd..610d6418 100644
--- a/lib/rules/require-meta-has-suggestions.ts
+++ b/lib/rules/require-meta-has-suggestions.ts
@@ -8,7 +8,7 @@ import {
   getKeyName,
   getRuleInfo,
   isUndefinedIdentifier,
-} from '../utils.js';
+} from '../utils.ts';
 
 // ------------------------------------------------------------------------------
 // Rule Definition
diff --git a/lib/rules/require-meta-schema-description.ts b/lib/rules/require-meta-schema-description.ts
index 2ffb8eea..80d36676 100644
--- a/lib/rules/require-meta-schema-description.ts
+++ b/lib/rules/require-meta-schema-description.ts
@@ -6,7 +6,7 @@ import {
   getMetaSchemaNode,
   getMetaSchemaNodeProperty,
   getRuleInfo,
-} from '../utils.js';
+} from '../utils.ts';
 
 // ------------------------------------------------------------------------------
 // Rule Definition
diff --git a/lib/rules/require-meta-schema.ts b/lib/rules/require-meta-schema.ts
index 909fdd58..ab1a5526 100644
--- a/lib/rules/require-meta-schema.ts
+++ b/lib/rules/require-meta-schema.ts
@@ -8,7 +8,7 @@ import {
   getRuleInfo,
   insertProperty,
   isUndefinedIdentifier,
-} from '../utils.js';
+} from '../utils.ts';
 
 // ------------------------------------------------------------------------------
 // Rule Definition
diff --git a/lib/rules/require-meta-type.ts b/lib/rules/require-meta-type.ts
index 7001936b..400d0297 100644
--- a/lib/rules/require-meta-type.ts
+++ b/lib/rules/require-meta-type.ts
@@ -5,7 +5,7 @@
 import { getStaticValue } from '@eslint-community/eslint-utils';
 import type { Rule } from 'eslint';
 
-import { evaluateObjectProperties, getKeyName, getRuleInfo } from '../utils.js';
+import { evaluateObjectProperties, getKeyName, getRuleInfo } from '../utils.ts';
 
 const VALID_TYPES = new Set(['problem', 'suggestion', 'layout']);
 
diff --git a/lib/rules/test-case-property-ordering.ts b/lib/rules/test-case-property-ordering.ts
index 50eee786..0d9be79c 100644
--- a/lib/rules/test-case-property-ordering.ts
+++ b/lib/rules/test-case-property-ordering.ts
@@ -4,7 +4,7 @@
  */
 import type { Rule } from 'eslint';
 
-import { getKeyName, getTestInfo } from '../utils.js';
+import { getKeyName, getTestInfo } from '../utils.ts';
 
 const defaultOrder = [
   'filename',
diff --git a/lib/rules/test-case-shorthand-strings.ts b/lib/rules/test-case-shorthand-strings.ts
index f88db02e..e2ea0414 100644
--- a/lib/rules/test-case-shorthand-strings.ts
+++ b/lib/rules/test-case-shorthand-strings.ts
@@ -4,8 +4,8 @@
  */
 import type { Rule } from 'eslint';
 
-import { getKeyName, getTestInfo } from '../utils.js';
-import type { TestInfo } from '../types.js';
+import { getKeyName, getTestInfo } from '../utils.ts';
+import type { TestInfo } from '../types.ts';
 
 // ------------------------------------------------------------------------------
 // Rule Definition
diff --git a/lib/utils.ts b/lib/utils.ts
index a4ad085d..5d901f3c 100644
--- a/lib/utils.ts
+++ b/lib/utils.ts
@@ -31,7 +31,7 @@ import type {
   RuleInfo,
   TestInfo,
   ViolationAndSuppressionData,
-} from './types.js';
+} from './types.ts';
 
 const functionTypes = new Set([
   'FunctionExpression',
diff --git a/package.json b/package.json
index 5aa5ee6f..73185c4e 100644
--- a/package.json
+++ b/package.json
@@ -11,14 +11,14 @@
   },
   "license": "MIT",
   "scripts": {
-    "build": "tsup",
+    "build": "tsdown",
     "format": "prettier --write .",
     "format:check": "prettier --check .",
     "lint": "npm-run-all --continue-on-error --aggregate-output --parallel lint:*",
     "lint:docs": "markdownlint \"**/*.md\"",
     "lint:eslint-docs": "npm-run-all -s build \"update:eslint-docs -- --check\"",
-    "lint:js": "eslint --cache --ignore-pattern \"**/*.md\"",
-    "lint:js-docs": "eslint --no-inline-config \"**/*.md\"",
+    "lint:js": "eslint --cache --ignore-pattern \"**/*.md\" --flag unstable_native_nodejs_ts_config",
+    "lint:js-docs": "eslint --no-inline-config \"**/*.md\" --flag unstable_native_nodejs_ts_config",
     "lint:package-json": "npmPkgJsonLint .",
     "release": "release-it",
     "test": "vitest run --coverage",
@@ -83,7 +83,7 @@
     "npm-run-all2": "^7.0.1",
     "prettier": "^3.6.2",
     "release-it": "^17.2.0",
-    "tsup": "^8.5.0",
+    "tsdown": "^0.13.3",
     "typescript": "^5.9.2",
     "typescript-eslint": "^8.39.0",
     "vitest": "^3.2.4"
diff --git a/tests/lib/index.ts b/tests/lib/index.ts
index 0eeda49d..ea1bd3d2 100644
--- a/tests/lib/index.ts
+++ b/tests/lib/index.ts
@@ -1,6 +1,6 @@
 import { describe, expect, it } from 'vitest';
 
-import plugin from '../../lib/index.js';
+import plugin from '../../lib/index.ts';
 
 describe('exported plugin', () => {
   describe('has a meta.docs.url property on each rule', () => {
diff --git a/tests/lib/rule-setup.ts b/tests/lib/rule-setup.ts
index 9006b490..8531dcfb 100644
--- a/tests/lib/rule-setup.ts
+++ b/tests/lib/rule-setup.ts
@@ -3,7 +3,7 @@ import path from 'node:path';
 
 import { assert, describe, it } from 'vitest';
 
-import plugin from '../../lib/index.js';
+import plugin from '../../lib/index.ts';
 
 const RULE_NAMES = Object.keys(plugin.rules) as Array<
   keyof typeof plugin.rules
diff --git a/tests/lib/rules/consistent-output.ts b/tests/lib/rules/consistent-output.ts
index e63d62f7..8daa2a4b 100644
--- a/tests/lib/rules/consistent-output.ts
+++ b/tests/lib/rules/consistent-output.ts
@@ -7,7 +7,7 @@
 // Requirements
 // ------------------------------------------------------------------------------
 
-import rule from '../../../lib/rules/consistent-output.js';
+import rule from '../../../lib/rules/consistent-output.ts';
 import { RuleTester } from 'eslint';
 
 const ERROR = { messageId: 'missingOutput', type: 'ObjectExpression' };
diff --git a/tests/lib/rules/fixer-return.ts b/tests/lib/rules/fixer-return.ts
index bff61ee3..b2bd56d9 100644
--- a/tests/lib/rules/fixer-return.ts
+++ b/tests/lib/rules/fixer-return.ts
@@ -7,7 +7,7 @@
 // Requirements
 // ------------------------------------------------------------------------------
 
-import rule from '../../../lib/rules/fixer-return.js';
+import rule from '../../../lib/rules/fixer-return.ts';
 import { RuleTester } from 'eslint';
 
 // ------------------------------------------------------------------------------
diff --git a/tests/lib/rules/meta-property-ordering.ts b/tests/lib/rules/meta-property-ordering.ts
index 632dfe59..e2cfd024 100644
--- a/tests/lib/rules/meta-property-ordering.ts
+++ b/tests/lib/rules/meta-property-ordering.ts
@@ -6,7 +6,7 @@
 // Requirements
 // ------------------------------------------------------------------------------
 
-import rule from '../../../lib/rules/meta-property-ordering.js';
+import rule from '../../../lib/rules/meta-property-ordering.ts';
 import { RuleTester } from 'eslint';
 
 // ------------------------------------------------------------------------------
diff --git a/tests/lib/rules/no-deprecated-context-methods.ts b/tests/lib/rules/no-deprecated-context-methods.ts
index 14eaaccc..0bb87056 100644
--- a/tests/lib/rules/no-deprecated-context-methods.ts
+++ b/tests/lib/rules/no-deprecated-context-methods.ts
@@ -7,7 +7,7 @@
 // Requirements
 // ------------------------------------------------------------------------------
 
-import rule from '../../../lib/rules/no-deprecated-context-methods.js';
+import rule from '../../../lib/rules/no-deprecated-context-methods.ts';
 import { RuleTester } from 'eslint';
 
 // ------------------------------------------------------------------------------
diff --git a/tests/lib/rules/no-deprecated-report-api.ts b/tests/lib/rules/no-deprecated-report-api.ts
index 636b2c11..419e8235 100644
--- a/tests/lib/rules/no-deprecated-report-api.ts
+++ b/tests/lib/rules/no-deprecated-report-api.ts
@@ -7,7 +7,7 @@
 // Requirements
 // ------------------------------------------------------------------------------
 
-import rule from '../../../lib/rules/no-deprecated-report-api.js';
+import rule from '../../../lib/rules/no-deprecated-report-api.ts';
 import { RuleTester } from 'eslint';
 
 // ------------------------------------------------------------------------------
diff --git a/tests/lib/rules/no-identical-tests.ts b/tests/lib/rules/no-identical-tests.ts
index 169d9140..1197b973 100644
--- a/tests/lib/rules/no-identical-tests.ts
+++ b/tests/lib/rules/no-identical-tests.ts
@@ -7,7 +7,7 @@
 // Requirements
 // ------------------------------------------------------------------------------
 
-import rule from '../../../lib/rules/no-identical-tests.js';
+import rule from '../../../lib/rules/no-identical-tests.ts';
 import { RuleTester } from 'eslint';
 
 const ERROR_OBJECT_TEST = { messageId: 'identical', type: 'ObjectExpression' };
diff --git a/tests/lib/rules/no-meta-replaced-by.ts b/tests/lib/rules/no-meta-replaced-by.ts
index f27fa93d..c3225de5 100644
--- a/tests/lib/rules/no-meta-replaced-by.ts
+++ b/tests/lib/rules/no-meta-replaced-by.ts
@@ -6,7 +6,7 @@
 // Requirements
 // ------------------------------------------------------------------------------
 
-import rule from '../../../lib/rules/no-meta-replaced-by.js';
+import rule from '../../../lib/rules/no-meta-replaced-by.ts';
 import { RuleTester } from 'eslint';
 
 // ------------------------------------------------------------------------------
diff --git a/tests/lib/rules/no-meta-schema-default.ts b/tests/lib/rules/no-meta-schema-default.ts
index 07dd50d1..26863096 100644
--- a/tests/lib/rules/no-meta-schema-default.ts
+++ b/tests/lib/rules/no-meta-schema-default.ts
@@ -2,7 +2,7 @@
 // Requirements
 // ------------------------------------------------------------------------------
 
-import rule from '../../../lib/rules/no-meta-schema-default.js';
+import rule from '../../../lib/rules/no-meta-schema-default.ts';
 import { RuleTester } from 'eslint';
 
 // ------------------------------------------------------------------------------
diff --git a/tests/lib/rules/no-missing-message-ids.ts b/tests/lib/rules/no-missing-message-ids.ts
index aa0045a0..e46014cf 100644
--- a/tests/lib/rules/no-missing-message-ids.ts
+++ b/tests/lib/rules/no-missing-message-ids.ts
@@ -2,7 +2,7 @@
 // Requirements
 // ------------------------------------------------------------------------------
 
-import rule from '../../../lib/rules/no-missing-message-ids.js';
+import rule from '../../../lib/rules/no-missing-message-ids.ts';
 import { RuleTester } from 'eslint';
 
 // ------------------------------------------------------------------------------
diff --git a/tests/lib/rules/no-missing-placeholders.ts b/tests/lib/rules/no-missing-placeholders.ts
index f725590e..e7290a65 100644
--- a/tests/lib/rules/no-missing-placeholders.ts
+++ b/tests/lib/rules/no-missing-placeholders.ts
@@ -7,7 +7,7 @@
 // Requirements
 // ------------------------------------------------------------------------------
 
-import rule from '../../../lib/rules/no-missing-placeholders.js';
+import rule from '../../../lib/rules/no-missing-placeholders.ts';
 import { RuleTester } from 'eslint';
 
 /**
diff --git a/tests/lib/rules/no-only-tests.ts b/tests/lib/rules/no-only-tests.ts
index b7f52125..8c091f8f 100644
--- a/tests/lib/rules/no-only-tests.ts
+++ b/tests/lib/rules/no-only-tests.ts
@@ -2,7 +2,7 @@
 // Requirements
 // ------------------------------------------------------------------------------
 
-import rule from '../../../lib/rules/no-only-tests.js';
+import rule from '../../../lib/rules/no-only-tests.ts';
 import { RuleTester } from 'eslint';
 
 // ------------------------------------------------------------------------------
diff --git a/tests/lib/rules/no-property-in-node.ts b/tests/lib/rules/no-property-in-node.ts
index c21e1cb1..57106ee1 100644
--- a/tests/lib/rules/no-property-in-node.ts
+++ b/tests/lib/rules/no-property-in-node.ts
@@ -1,7 +1,7 @@
 import { RuleTester } from 'eslint';
 import path from 'node:path';
 import { fileURLToPath } from 'node:url';
-import rule from '../../../lib/rules/no-property-in-node.js';
+import rule from '../../../lib/rules/no-property-in-node.ts';
 import parser from '@typescript-eslint/parser';
 
 const dirname = path.dirname(fileURLToPath(import.meta.url));
diff --git a/tests/lib/rules/no-unused-message-ids.ts b/tests/lib/rules/no-unused-message-ids.ts
index 244651e1..ff69b435 100644
--- a/tests/lib/rules/no-unused-message-ids.ts
+++ b/tests/lib/rules/no-unused-message-ids.ts
@@ -2,7 +2,7 @@
 // Requirements
 // ------------------------------------------------------------------------------
 
-import rule from '../../../lib/rules/no-unused-message-ids.js';
+import rule from '../../../lib/rules/no-unused-message-ids.ts';
 import { RuleTester } from 'eslint';
 
 // ------------------------------------------------------------------------------
diff --git a/tests/lib/rules/no-unused-placeholders.ts b/tests/lib/rules/no-unused-placeholders.ts
index 9f16166b..11ae3b98 100644
--- a/tests/lib/rules/no-unused-placeholders.ts
+++ b/tests/lib/rules/no-unused-placeholders.ts
@@ -7,7 +7,7 @@
 // Requirements
 // ------------------------------------------------------------------------------
 
-import rule from '../../../lib/rules/no-unused-placeholders.js';
+import rule from '../../../lib/rules/no-unused-placeholders.ts';
 import { RuleTester } from 'eslint';
 
 /**
diff --git a/tests/lib/rules/no-useless-token-range.ts b/tests/lib/rules/no-useless-token-range.ts
index 72499c80..1ce88722 100644
--- a/tests/lib/rules/no-useless-token-range.ts
+++ b/tests/lib/rules/no-useless-token-range.ts
@@ -7,7 +7,7 @@
 // Requirements
 // ------------------------------------------------------------------------------
 
-import rule from '../../../lib/rules/no-useless-token-range.js';
+import rule from '../../../lib/rules/no-useless-token-range.ts';
 import { RuleTester } from 'eslint';
 
 /**
diff --git a/tests/lib/rules/prefer-message-ids.ts b/tests/lib/rules/prefer-message-ids.ts
index 9a45cb28..aebd16d4 100644
--- a/tests/lib/rules/prefer-message-ids.ts
+++ b/tests/lib/rules/prefer-message-ids.ts
@@ -2,7 +2,7 @@
 // Requirements
 // ------------------------------------------------------------------------------
 
-import rule from '../../../lib/rules/prefer-message-ids.js';
+import rule from '../../../lib/rules/prefer-message-ids.ts';
 import { RuleTester } from 'eslint';
 
 // ------------------------------------------------------------------------------
diff --git a/tests/lib/rules/prefer-object-rule.ts b/tests/lib/rules/prefer-object-rule.ts
index 4c25013c..4eda2ba8 100644
--- a/tests/lib/rules/prefer-object-rule.ts
+++ b/tests/lib/rules/prefer-object-rule.ts
@@ -6,7 +6,7 @@
 // Requirements
 // ------------------------------------------------------------------------------
 
-import rule from '../../../lib/rules/prefer-object-rule.js';
+import rule from '../../../lib/rules/prefer-object-rule.ts';
 import { RuleTester } from 'eslint';
 
 // ------------------------------------------------------------------------------
diff --git a/tests/lib/rules/prefer-output-null.ts b/tests/lib/rules/prefer-output-null.ts
index 082e41c4..afdfa649 100644
--- a/tests/lib/rules/prefer-output-null.ts
+++ b/tests/lib/rules/prefer-output-null.ts
@@ -7,7 +7,7 @@
 // Requirements
 // ------------------------------------------------------------------------------
 
-import rule from '../../../lib/rules/prefer-output-null.js';
+import rule from '../../../lib/rules/prefer-output-null.ts';
 import { RuleTester } from 'eslint';
 
 const ERROR = { messageId: 'useOutputNull', type: 'Property' };
diff --git a/tests/lib/rules/prefer-placeholders.ts b/tests/lib/rules/prefer-placeholders.ts
index 4b2f6447..f2051f09 100644
--- a/tests/lib/rules/prefer-placeholders.ts
+++ b/tests/lib/rules/prefer-placeholders.ts
@@ -7,7 +7,7 @@
 // Requirements
 // ------------------------------------------------------------------------------
 
-import rule from '../../../lib/rules/prefer-placeholders.js';
+import rule from '../../../lib/rules/prefer-placeholders.ts';
 import { RuleTester } from 'eslint';
 
 // ------------------------------------------------------------------------------
diff --git a/tests/lib/rules/prefer-replace-text.ts b/tests/lib/rules/prefer-replace-text.ts
index 06117252..e3d8b7eb 100644
--- a/tests/lib/rules/prefer-replace-text.ts
+++ b/tests/lib/rules/prefer-replace-text.ts
@@ -7,7 +7,7 @@
 // Requirements
 // ------------------------------------------------------------------------------
 
-import rule from '../../../lib/rules/prefer-replace-text.js';
+import rule from '../../../lib/rules/prefer-replace-text.ts';
 import { RuleTester } from 'eslint';
 
 // ------------------------------------------------------------------------------
diff --git a/tests/lib/rules/report-message-format.ts b/tests/lib/rules/report-message-format.ts
index dd7f9e61..37331322 100644
--- a/tests/lib/rules/report-message-format.ts
+++ b/tests/lib/rules/report-message-format.ts
@@ -7,7 +7,7 @@
 // Requirements
 // ------------------------------------------------------------------------------
 
-import rule from '../../../lib/rules/report-message-format.js';
+import rule from '../../../lib/rules/report-message-format.ts';
 import { RuleTester } from 'eslint';
 
 // ------------------------------------------------------------------------------
diff --git a/tests/lib/rules/require-meta-default-options.ts b/tests/lib/rules/require-meta-default-options.ts
index d6ceb410..81c3de98 100644
--- a/tests/lib/rules/require-meta-default-options.ts
+++ b/tests/lib/rules/require-meta-default-options.ts
@@ -1,4 +1,4 @@
-import rule from '../../../lib/rules/require-meta-default-options.js';
+import rule from '../../../lib/rules/require-meta-default-options.ts';
 import { RuleTester } from 'eslint';
 import parser from '@typescript-eslint/parser';
 
diff --git a/tests/lib/rules/require-meta-docs-description.ts b/tests/lib/rules/require-meta-docs-description.ts
index 28d49910..10f37b3e 100644
--- a/tests/lib/rules/require-meta-docs-description.ts
+++ b/tests/lib/rules/require-meta-docs-description.ts
@@ -2,7 +2,7 @@
 // Requirements
 // ------------------------------------------------------------------------------
 
-import rule from '../../../lib/rules/require-meta-docs-description.js';
+import rule from '../../../lib/rules/require-meta-docs-description.ts';
 import { RuleTester } from 'eslint';
 import parser from '@typescript-eslint/parser';
 
diff --git a/tests/lib/rules/require-meta-docs-recommended.ts b/tests/lib/rules/require-meta-docs-recommended.ts
index 60a9d72a..8d709e58 100644
--- a/tests/lib/rules/require-meta-docs-recommended.ts
+++ b/tests/lib/rules/require-meta-docs-recommended.ts
@@ -1,4 +1,4 @@
-import rule from '../../../lib/rules/require-meta-docs-recommended.js';
+import rule from '../../../lib/rules/require-meta-docs-recommended.ts';
 import { RuleTester } from 'eslint';
 import parser from '@typescript-eslint/parser';
 
diff --git a/tests/lib/rules/require-meta-docs-url.ts b/tests/lib/rules/require-meta-docs-url.ts
index 50895f05..e4e9b31c 100644
--- a/tests/lib/rules/require-meta-docs-url.ts
+++ b/tests/lib/rules/require-meta-docs-url.ts
@@ -9,7 +9,7 @@
 // -----------------------------------------------------------------------------
 
 import { RuleTester } from 'eslint';
-import rule from '../../../lib/rules/require-meta-docs-url.js';
+import rule from '../../../lib/rules/require-meta-docs-url.ts';
 
 // -----------------------------------------------------------------------------
 // Tests
diff --git a/tests/lib/rules/require-meta-fixable.ts b/tests/lib/rules/require-meta-fixable.ts
index 3bde53c7..f0210ec2 100644
--- a/tests/lib/rules/require-meta-fixable.ts
+++ b/tests/lib/rules/require-meta-fixable.ts
@@ -7,7 +7,7 @@
 // Requirements
 // ------------------------------------------------------------------------------
 
-import rule from '../../../lib/rules/require-meta-fixable.js';
+import rule from '../../../lib/rules/require-meta-fixable.ts';
 import { RuleTester } from 'eslint';
 
 // ------------------------------------------------------------------------------
diff --git a/tests/lib/rules/require-meta-has-suggestions.ts b/tests/lib/rules/require-meta-has-suggestions.ts
index 8bb7eb84..cf669e5a 100644
--- a/tests/lib/rules/require-meta-has-suggestions.ts
+++ b/tests/lib/rules/require-meta-has-suggestions.ts
@@ -2,7 +2,7 @@
 // Requirements
 // ------------------------------------------------------------------------------
 
-import rule from '../../../lib/rules/require-meta-has-suggestions.js';
+import rule from '../../../lib/rules/require-meta-has-suggestions.ts';
 import { RuleTester } from 'eslint';
 
 // ------------------------------------------------------------------------------
diff --git a/tests/lib/rules/require-meta-schema-description.ts b/tests/lib/rules/require-meta-schema-description.ts
index fa0b414f..a9428da7 100644
--- a/tests/lib/rules/require-meta-schema-description.ts
+++ b/tests/lib/rules/require-meta-schema-description.ts
@@ -2,7 +2,7 @@
 // Requirements
 // ------------------------------------------------------------------------------
 
-import rule from '../../../lib/rules/require-meta-schema-description.js';
+import rule from '../../../lib/rules/require-meta-schema-description.ts';
 import { RuleTester } from 'eslint';
 
 // ------------------------------------------------------------------------------
diff --git a/tests/lib/rules/require-meta-schema.ts b/tests/lib/rules/require-meta-schema.ts
index 5c6c6af0..6bc9b900 100644
--- a/tests/lib/rules/require-meta-schema.ts
+++ b/tests/lib/rules/require-meta-schema.ts
@@ -2,7 +2,7 @@
 // Requirements
 // ------------------------------------------------------------------------------
 
-import rule from '../../../lib/rules/require-meta-schema.js';
+import rule from '../../../lib/rules/require-meta-schema.ts';
 import { RuleTester } from 'eslint';
 
 // ------------------------------------------------------------------------------
diff --git a/tests/lib/rules/require-meta-type.ts b/tests/lib/rules/require-meta-type.ts
index 645bf7ec..b3f48a35 100644
--- a/tests/lib/rules/require-meta-type.ts
+++ b/tests/lib/rules/require-meta-type.ts
@@ -7,7 +7,7 @@
 // Requirements
 // ------------------------------------------------------------------------------
 
-import rule from '../../../lib/rules/require-meta-type.js';
+import rule from '../../../lib/rules/require-meta-type.ts';
 import { RuleTester } from 'eslint';
 
 // ------------------------------------------------------------------------------
diff --git a/tests/lib/rules/test-case-property-ordering.ts b/tests/lib/rules/test-case-property-ordering.ts
index 05fb8554..e3dae7b3 100644
--- a/tests/lib/rules/test-case-property-ordering.ts
+++ b/tests/lib/rules/test-case-property-ordering.ts
@@ -7,7 +7,7 @@
 // Requirements
 // ------------------------------------------------------------------------------
 
-import rule from '../../../lib/rules/test-case-property-ordering.js';
+import rule from '../../../lib/rules/test-case-property-ordering.ts';
 import { RuleTester } from 'eslint';
 
 // ------------------------------------------------------------------------------
diff --git a/tests/lib/rules/test-case-shorthand-strings.ts b/tests/lib/rules/test-case-shorthand-strings.ts
index 0b989397..729f72e8 100644
--- a/tests/lib/rules/test-case-shorthand-strings.ts
+++ b/tests/lib/rules/test-case-shorthand-strings.ts
@@ -7,7 +7,7 @@
 // Requirements
 // ------------------------------------------------------------------------------
 
-import rule from '../../../lib/rules/test-case-shorthand-strings.js';
+import rule from '../../../lib/rules/test-case-shorthand-strings.ts';
 import { RuleTester } from 'eslint';
 
 /**
diff --git a/tests/lib/utils.ts b/tests/lib/utils.ts
index 46c86f22..8e180210 100644
--- a/tests/lib/utils.ts
+++ b/tests/lib/utils.ts
@@ -7,7 +7,7 @@ import * as estraverse from 'estraverse';
 import lodash from 'lodash';
 import { assert, describe, it } from 'vitest';
 
-import * as utils from '../../lib/utils.js';
+import * as utils from '../../lib/utils.ts';
 import type {
   ArrayExpression,
   ArrowFunctionExpression,
@@ -29,7 +29,7 @@ import type {
   VariableDeclaration,
 } from 'estree';
 import type { Rule, Scope } from 'eslint';
-import type { RuleInfo } from '../../lib/types.js';
+import type { RuleInfo } from '../../lib/types.ts';
 
 type MockRuleInfo = {
   create: {
diff --git a/tsconfig.json b/tsconfig.json
index 1411ce1d..3a7aa70f 100644
--- a/tsconfig.json
+++ b/tsconfig.json
@@ -13,6 +13,7 @@
     "verbatimModuleSyntax": true,
     "erasableSyntaxOnly": true,
     "forceConsistentCasingInFileNames": true,
+    "rewriteRelativeImportExtensions": true,
     "paths": {
       "eslint-plugin-eslint-plugin": ["./lib/index.ts"]
     },
diff --git a/tsup.config.ts b/tsdown.config.ts
similarity index 51%
rename from tsup.config.ts
rename to tsdown.config.ts
index 3542a8da..512d1243 100644
--- a/tsup.config.ts
+++ b/tsdown.config.ts
@@ -1,10 +1,8 @@
-import { defineConfig } from 'tsup';
+import { defineConfig } from 'tsdown';
 
 export default defineConfig({
-  bundle: false,
-  clean: true,
+  unbundle: true,
   dts: true,
   entry: ['lib/**/*.ts'],
-  format: ['esm'],
   outDir: 'dist',
 });