diff --git a/packages/compiler/eslint.config.mjs b/packages/compiler/eslint.config.mjs
index 5997309..f1ff2be 100644
--- a/packages/compiler/eslint.config.mjs
+++ b/packages/compiler/eslint.config.mjs
@@ -3,6 +3,7 @@ import tempblotPreset from 'tempblot-config/eslint-preset.js'
 export default [
   ...tempblotPreset,
   {
+    files: ['**/*.ts', '**/*.tsx', '**/*.mts', '**/*.cts'],
     languageOptions: {
       parserOptions: {
         projectService: true,
diff --git a/packages/compiler/src/index.ts b/packages/compiler/src/index.ts
index f90ec3b..d441fcc 100644
--- a/packages/compiler/src/index.ts
+++ b/packages/compiler/src/index.ts
@@ -5,9 +5,9 @@ import {
   tokenizeRoot,
   transformOutputTemplate,
 } from "tempblot-parser";
-import { transformSetup } from "./setup-transformer.js";
+import { transformSetup } from "./setup-transformer.ts";
 
-export { TempblotInstance, useParams } from "./instance.js";
+export { TempblotInstance, useParams } from "./instance.ts";
 
 declare global {
   var tempblotParams: Record<string, unknown> | undefined;
@@ -40,7 +40,11 @@ export async function compilePath<TParams = unknown>(
   const tempPath = path.join(sourceDir, `.tempblot_${outputVarName}.ts`);
   try {
     await fs.writeFile(tempPath, concatenatedSetupOutput);
-    const compiledOutput: string = (await import(tempPath))[outputVarName];
+    const compiledModule = (await import(tempPath)) as Record<string, unknown>;
+    const compiledOutput = compiledModule[outputVarName];
+    if (typeof compiledOutput !== "string") {
+      throw new TypeError("Tempblot output must compile to a string");
+    }
     return compiledOutput;
   } finally {
     await fs.unlink(tempPath);
diff --git a/packages/compiler/src/instance.ts b/packages/compiler/src/instance.ts
index 668ae6a..ad53385 100644
--- a/packages/compiler/src/instance.ts
+++ b/packages/compiler/src/instance.ts
@@ -1,3 +1,5 @@
+// An interface so we can interface merge in the future from external sources
+// eslint-disable-next-line @typescript-eslint/no-empty-object-type
 export interface TempblotParams {}
 
 export class TempblotInstance<TParams = TempblotParams> {
diff --git a/packages/compiler/tests/index.spec.ts b/packages/compiler/tests/index.spec.ts
index b2be1e4..5cc4b8e 100644
--- a/packages/compiler/tests/index.spec.ts
+++ b/packages/compiler/tests/index.spec.ts
@@ -4,7 +4,7 @@ import { dirname } from "node:path";
 
 import { test, expect } from "vitest";
 
-import { compilePath, useParams } from "../src/index.js";
+import { compilePath, useParams } from "../src/index.ts";
 
 const __filename = fileURLToPath(import.meta.url);
 const __dirname = dirname(__filename);
diff --git a/packages/compiler/tests/setup-transformer.spec.ts b/packages/compiler/tests/setup-transformer.spec.ts
index 6bc0540..088901f 100644
--- a/packages/compiler/tests/setup-transformer.spec.ts
+++ b/packages/compiler/tests/setup-transformer.spec.ts
@@ -1,5 +1,5 @@
 import { expect, test } from "vitest";
-import { transformSetup } from "../src/setup-transformer.js";
+import { transformSetup } from "../src/setup-transformer.ts";
 
 const sourcePath = "/path/to/somefile.tempblot";
 
diff --git a/packages/config/eslint-preset.js b/packages/config/eslint-preset.js
index 2dba202..29983f4 100644
--- a/packages/config/eslint-preset.js
+++ b/packages/config/eslint-preset.js
@@ -20,12 +20,12 @@ export const tempblotJSRules = {
     {
       patterns: [
         {
-          regex: '\.\.?\/.*\.js',
+          regex: '^\.\.?\/.*\.js$',
           message:
             "importing `.js` files is not supported by Node's built-in TypeScript support. Use `.ts` instead.",
         },
         {
-          regex: '^\\./(?!.*\\.(?:ts|tsx|mts|cts|js|jsx|mjs|cjs)$)',
+          regex: '^\\./(?!.*\\.(?:ts|tsx|mts|cts|js|jsx|mjs|cjs|json)$)',
           message:
             'Relative imports must include the file extension. For example, use `import foo from "./foo.ts"` instead of `import foo from "./foo"`.',
         },
@@ -55,6 +55,10 @@ export default defineConfig(
   {
     // - `eslint-preset.js`: the preset bootstraps itself, ignoring
     //   keeps eslint from re-evaluating it under the typed rules.
-    ignores: ['eslint-preset.js', '**/dist/**', '**/lib/**', '**/out/**'],
+    ignores: [
+      'eslint-preset.js',
+      '**/dist/**',
+      '**/out/**',
+    ],
   },
 )
diff --git a/packages/language-server/eslint.config.mjs b/packages/language-server/eslint.config.mjs
index 5997309..7eb16fa 100644
--- a/packages/language-server/eslint.config.mjs
+++ b/packages/language-server/eslint.config.mjs
@@ -3,6 +3,7 @@ import tempblotPreset from 'tempblot-config/eslint-preset.js'
 export default [
   ...tempblotPreset,
   {
+    files: ['**/*.ts', '**/*.tsx', '**/*.mts', '**/*.cts'],
     languageOptions: {
       parserOptions: {
         projectService: true,
@@ -17,6 +18,6 @@ export default [
     },
   },
   {
-    ignores: ['eslint.config.mjs'],
+    ignores: ['eslint.config.mjs', 'lib/**'],
   },
 ]
diff --git a/packages/language-server/src/index.ts b/packages/language-server/src/index.ts
index e6d2968..72f016f 100644
--- a/packages/language-server/src/index.ts
+++ b/packages/language-server/src/index.ts
@@ -23,12 +23,7 @@ const connection = createConnection();
 const server = createServer(connection);
 
 connection.onInitialize(async (parameters: InitializeParams): Promise<InitializeResult> => {
-  const tsdk = parameters.initializationOptions?.typescript?.tsdk;
-  
-  assert.ok(
-    typeof tsdk === 'string',
-    'Missing initialization option typescript.tsdk'
-  );
+  const tsdk = getTsdk(parameters);
 
   const { typescript, diagnosticMessages } = loadTsdkByPath(
     tsdk,
@@ -52,7 +47,33 @@ connection.onInitialize(async (parameters: InitializeParams): Promise<Initialize
 
 connection.onInitialized(() => {
   server.initialized();
-  server.fileWatcher?.watchFiles(['**/*.blot']);
+  void server.fileWatcher?.watchFiles(['**/*.blot']);
 });
 
 connection.listen();
+
+function getTsdk(parameters: InitializeParams): string {
+  const initializationOptions: unknown = parameters.initializationOptions;
+  assert.ok(
+    initializationOptions !== null &&
+      typeof initializationOptions === 'object' &&
+      'typescript' in initializationOptions,
+    'Missing initialization option typescript.tsdk'
+  );
+
+  const typescriptOptions: unknown = initializationOptions.typescript;
+  assert.ok(
+    typescriptOptions !== null &&
+      typeof typescriptOptions === 'object' &&
+      'tsdk' in typescriptOptions,
+    'Missing initialization option typescript.tsdk'
+  );
+
+  const tsdk: unknown = typescriptOptions.tsdk;
+  assert.ok(
+    typeof tsdk === 'string',
+    'Missing initialization option typescript.tsdk'
+  );
+
+  return tsdk;
+}
diff --git a/packages/language-service/eslint.config.mjs b/packages/language-service/eslint.config.mjs
index 5997309..7eb16fa 100644
--- a/packages/language-service/eslint.config.mjs
+++ b/packages/language-service/eslint.config.mjs
@@ -3,6 +3,7 @@ import tempblotPreset from 'tempblot-config/eslint-preset.js'
 export default [
   ...tempblotPreset,
   {
+    files: ['**/*.ts', '**/*.tsx', '**/*.mts', '**/*.cts'],
     languageOptions: {
       parserOptions: {
         projectService: true,
@@ -17,6 +18,6 @@ export default [
     },
   },
   {
-    ignores: ['eslint.config.mjs'],
+    ignores: ['eslint.config.mjs', 'lib/**'],
   },
 ]
diff --git a/packages/language-service/src/index.ts b/packages/language-service/src/index.ts
index b194bae..f700129 100644
--- a/packages/language-service/src/index.ts
+++ b/packages/language-service/src/index.ts
@@ -1,2 +1,2 @@
-export { createTempblotLanguagePlugin, TempblotVirtualCode } from './language-plugin.js';
-export { createTempblotServicePlugin } from './service-plugin.js';
+export { createTempblotLanguagePlugin, TempblotVirtualCode } from './language-plugin.ts';
+export { createTempblotServicePlugin } from './service-plugin.ts';
diff --git a/packages/language-service/src/language-plugin.ts b/packages/language-service/src/language-plugin.ts
index 3cdabca..f0713e0 100644
--- a/packages/language-service/src/language-plugin.ts
+++ b/packages/language-service/src/language-plugin.ts
@@ -156,7 +156,7 @@ function* getTempblotEmbeddedCodes(
       const expressionStart =
         interpStartOffset + `(`.length;
       tsInterpolationMappings.push({
-        sourceOffsets: [output.startTagEnd! + interp.sourceStart],
+        sourceOffsets: [output.startTagEnd + interp.sourceStart],
         generatedOffsets: [expressionStart],
         lengths: [interp.expression.length],
         data: {
diff --git a/packages/language-service/src/service-plugin.ts b/packages/language-service/src/service-plugin.ts
index 24237ae..e461151 100644
--- a/packages/language-service/src/service-plugin.ts
+++ b/packages/language-service/src/service-plugin.ts
@@ -1,15 +1,24 @@
-import { Diagnostic } from '@volar/language-service';
+import type {
+  Diagnostic,
+  LanguageServiceContext,
+  LanguageServicePlugin,
+  LanguageServicePluginInstance,
+} from '@volar/language-service';
 import { URI } from 'vscode-uri';
-import { TempblotVirtualCode } from './language-plugin.js';
+import { TempblotVirtualCode } from './language-plugin.ts';
 
-export function createTempblotServicePlugin() {
+type DiagnosticsDocument = Parameters<
+  NonNullable<LanguageServicePluginInstance['provideDiagnostics']>
+>[0];
+
+export function createTempblotServicePlugin(): LanguageServicePlugin {
   return {
     capabilities: {
       diagnosticProvider: { interFileDependencies: false, workspaceDiagnostics: false },
     },
-    create(context: any) {
+    create(context: LanguageServiceContext) {
       return {
-        provideDiagnostics(document: any) {
+        provideDiagnostics(document: DiagnosticsDocument) {
           const decoded = context.decodeEmbeddedDocumentUri(URI.parse(document.uri));
           if (!decoded) {
             // Not a embedded document
diff --git a/packages/parser/eslint.config.mjs b/packages/parser/eslint.config.mjs
index 5997309..b3931d8 100644
--- a/packages/parser/eslint.config.mjs
+++ b/packages/parser/eslint.config.mjs
@@ -3,9 +3,12 @@ import tempblotPreset from 'tempblot-config/eslint-preset.js'
 export default [
   ...tempblotPreset,
   {
+    files: ['**/*.ts', '**/*.tsx', '**/*.mts', '**/*.cts'],
     languageOptions: {
       parserOptions: {
-        projectService: true,
+        projectService: {
+          allowDefaultProject: ['tests/*.ts', 'vite.config.ts'],
+        },
         tsconfigRootDir: import.meta.dirname,
       },
     },
@@ -17,6 +20,6 @@ export default [
     },
   },
   {
-    ignores: ['eslint.config.mjs'],
+    ignores: ['eslint.config.mjs', 'lib/**'],
   },
 ]
diff --git a/packages/parser/tests/output-transformer.spec.ts b/packages/parser/tests/output-transformer.spec.ts
index 211776b..70a20d0 100644
--- a/packages/parser/tests/output-transformer.spec.ts
+++ b/packages/parser/tests/output-transformer.spec.ts
@@ -1,5 +1,5 @@
 import { expect, test } from "vitest";
-import { transformOutputTemplate } from "../src/index.js";
+import { transformOutputTemplate } from "../src/index.ts";
 
 test("transformOutputTemplate", () => {
   const source = 'const someStr = `<div><<val ? "\\>\\>" : "\\<\\<">></div>`;';
diff --git a/packages/parser/tests/root-lexer.spec.ts b/packages/parser/tests/root-lexer.spec.ts
index 9a00e9d..7973b6b 100644
--- a/packages/parser/tests/root-lexer.spec.ts
+++ b/packages/parser/tests/root-lexer.spec.ts
@@ -1,5 +1,5 @@
 import { expect, test } from "vitest";
-import { tokenizeRoot } from "../src/index.js";
+import { tokenizeRoot } from "../src/index.ts";
 
 function withoutOffsets(value: unknown): unknown {
   if (Array.isArray(value)) {
diff --git a/packages/parser/tests/root-parser.spec.ts b/packages/parser/tests/root-parser.spec.ts
index 84e6754..290ce13 100644
--- a/packages/parser/tests/root-parser.spec.ts
+++ b/packages/parser/tests/root-parser.spec.ts
@@ -1,5 +1,5 @@
 import { expect, test } from "vitest";
-import { parseRoot, tokenizeRoot } from "../src/index.js";
+import { parseRoot, tokenizeRoot } from "../src/index.ts";
 
 const source = `
 <setup>
diff --git a/packages/prettier-plugin/eslint.config.mjs b/packages/prettier-plugin/eslint.config.mjs
index 5997309..b3931d8 100644
--- a/packages/prettier-plugin/eslint.config.mjs
+++ b/packages/prettier-plugin/eslint.config.mjs
@@ -3,9 +3,12 @@ import tempblotPreset from 'tempblot-config/eslint-preset.js'
 export default [
   ...tempblotPreset,
   {
+    files: ['**/*.ts', '**/*.tsx', '**/*.mts', '**/*.cts'],
     languageOptions: {
       parserOptions: {
-        projectService: true,
+        projectService: {
+          allowDefaultProject: ['tests/*.ts', 'vite.config.ts'],
+        },
         tsconfigRootDir: import.meta.dirname,
       },
     },
@@ -17,6 +20,6 @@ export default [
     },
   },
   {
-    ignores: ['eslint.config.mjs'],
+    ignores: ['eslint.config.mjs', 'lib/**'],
   },
 ]
diff --git a/packages/prettier-plugin/tests/index.spec.ts b/packages/prettier-plugin/tests/index.spec.ts
index 58a3831..506a7c8 100644
--- a/packages/prettier-plugin/tests/index.spec.ts
+++ b/packages/prettier-plugin/tests/index.spec.ts
@@ -6,7 +6,7 @@ import { render } from "cli-testing-library";
 import * as prettier from "prettier";
 import { expect, test } from "vitest";
 
-import plugin from "../src/index.js";
+import plugin from "../src/index.ts";
 
 const __filename = fileURLToPath(import.meta.url);
 const __dirname = path.dirname(__filename);
diff --git a/packages/typescript-plugin/eslint.config.mjs b/packages/typescript-plugin/eslint.config.mjs
index 5997309..04e5a5d 100644
--- a/packages/typescript-plugin/eslint.config.mjs
+++ b/packages/typescript-plugin/eslint.config.mjs
@@ -3,6 +3,7 @@ import tempblotPreset from 'tempblot-config/eslint-preset.js'
 export default [
   ...tempblotPreset,
   {
+    files: ['**/*.ts', '**/*.tsx', '**/*.mts', '**/*.cts'],
     languageOptions: {
       parserOptions: {
         projectService: true,
@@ -16,6 +17,18 @@ export default [
       '@typescript-eslint/require-await': 'off',
     },
   },
+  {
+    files: ['lib/**/*.cjs'],
+    languageOptions: {
+      globals: {
+        module: 'readonly',
+        require: 'readonly',
+      },
+    },
+    rules: {
+      '@typescript-eslint/no-require-imports': 'off',
+    },
+  },
   {
     ignores: ['eslint.config.mjs'],
   },
diff --git a/packages/vscode/eslint.config.mjs b/packages/vscode/eslint.config.mjs
index 5997309..f1ff2be 100644
--- a/packages/vscode/eslint.config.mjs
+++ b/packages/vscode/eslint.config.mjs
@@ -3,6 +3,7 @@ import tempblotPreset from 'tempblot-config/eslint-preset.js'
 export default [
   ...tempblotPreset,
   {
+    files: ['**/*.ts', '**/*.tsx', '**/*.mts', '**/*.cts'],
     languageOptions: {
       parserOptions: {
         projectService: true,
diff --git a/packages/vscode/scripts/build.mjs b/packages/vscode/scripts/build.mjs
index 4850e5c..8c63a59 100644
--- a/packages/vscode/scripts/build.mjs
+++ b/packages/vscode/scripts/build.mjs
@@ -1,7 +1,7 @@
 #!/usr/bin/env node
 import {createRequire} from 'node:module'
 import process from 'node:process'
-import {fileURLToPath} from 'node:url'
+import {URL, fileURLToPath} from 'node:url'
 import {build} from 'esbuild'
 
 const require = createRequire(import.meta.url)
diff --git a/packages/vscode/src/extension.ts b/packages/vscode/src/extension.ts
index 0f0f48d..8bc0ce7 100644
--- a/packages/vscode/src/extension.ts
+++ b/packages/vscode/src/extension.ts
@@ -42,13 +42,13 @@ export async function activate(context: ExtensionContext) {
   );
 
   // Start server initially if enabled
-  tryRestartServer();
+  void tryRestartServer();
 
   // Watch for configuration changes
   context.subscriptions.push(
     workspace.onDidChangeConfiguration((event) => {
       if (event.affectsConfiguration('tempblot.server.enable')) {
-        tryRestartServer();
+        void tryRestartServer();
       }
     })
   );
diff --git a/tsconfig.base.json b/tsconfig.base.json
index 7ff5a96..6f95c3a 100644
--- a/tsconfig.base.json
+++ b/tsconfig.base.json
@@ -11,6 +11,8 @@
 		"declaration": true,
 		"strict": true,
 		"skipLibCheck": true,
+		"allowImportingTsExtensions": true,
+		"rewriteRelativeImportExtensions": true,
 		"noUnusedLocals": true,
 		"noUnusedParameters": true
 	},