diff --git a/.vscode/launch.json b/.vscode/launch.json
index 7a57f633..40f586ce 100644
--- a/.vscode/launch.json
+++ b/.vscode/launch.json
@@ -16,11 +16,11 @@
 			"request": "launch",
 			"runtimeArgs": [
 				"--test",
-				"./lib/umd/test/**/*.test.js"
+				"./lib/esm/test/**/*.test.js"
 			],
 			"cwd": "${workspaceRoot}",
 			"sourceMaps": true,
-			"outFiles": [ "${workspaceRoot}/lib/umd/**/*.js" ],
+			"outFiles": [ "${workspaceRoot}/lib/esm/**/*.js" ],
 			"preLaunchTask": "npm: watch"
 		},
 		{
diff --git a/build/bundle-schemas.cjs b/build/bundle-schemas.js
similarity index 90%
rename from build/bundle-schemas.cjs
rename to build/bundle-schemas.js
index 220e2ff6..76b538c2 100644
--- a/build/bundle-schemas.cjs
+++ b/build/bundle-schemas.js
@@ -3,23 +3,23 @@
  *  Licensed under the MIT License. See License.txt in the project root for license information.
  *--------------------------------------------------------------------------------------------*/
 
-const fs = require('fs').promises;
-const Bundler = require("@hyperjump/json-schema-bundle");
+import { writeFile } from 'node:fs/promises';
+import Bundler from '@hyperjump/json-schema-bundle';
 
 (async function () {
-	bundle(`https://json-schema.org/draft/2019-09/schema`, 'draft-2019-09', 'https://json-schema.org/draft/2019-09');
-	bundle(`https://json-schema.org/draft/2020-12/schema`, 'draft-2020-12', 'https://json-schema.org/draft/2020-12');
+	bundle('https://json-schema.org/draft/2019-09/schema', 'draft-2019-09', 'https://json-schema.org/draft/2019-09');
+	bundle('https://json-schema.org/draft/2020-12/schema', 'draft-2020-12', 'https://json-schema.org/draft/2020-12');
 }());
 
 async function bundle(uri, filename, derivedURL) {
 	const metaSchema = await Bundler.get(uri);
 	let bundle = await Bundler.bundle(metaSchema);
 	bundle = JSON.parse(JSON.stringify(bundle, null, 2).replace(/"undefined": ""/g, '"$dynamicAnchor": "meta"'));
-	fs.writeFile(`./${filename}.json`, JSON.stringify(bundle, null, 2), 'utf8');
+	await writeFile(`./${filename}.json`, JSON.stringify(bundle, null, 2), 'utf8');
 	bundle = flattenDraftMetaSchema(bundle);
 	const jsified = getCopyright(derivedURL) + 'export default ' + printObject(bundle);
-	fs.writeFile(`./${filename}-flat.json`, JSON.stringify(bundle, null, 2), 'utf8');
-	fs.writeFile(`./src/services/schemas/${filename}-flat.ts`, jsified, 'utf8');
+	await writeFile(`./${filename}-flat.json`, JSON.stringify(bundle, null, 2), 'utf8');
+	await writeFile(`./src/services/schemas/${filename}-flat.ts`, jsified, 'utf8');
 }
 function getCopyright(derivedURL) {
 	return [
@@ -55,7 +55,7 @@ function indent(level) {
 function printObject(obj, indentLevel = 0) {
 	const result = [];
 	if (Array.isArray(obj)) {
-		result.push(`[`);
+		result.push('[');
 		for (const item of obj) {
 			if (typeof item === 'object' && item !== null) {
 				result.push(`${indent(indentLevel + 1)}${printObject(item, indentLevel + 1)},`);
@@ -67,11 +67,11 @@ function printObject(obj, indentLevel = 0) {
 		return result.join('\n');
 	}
 	if (obj === null) {
-		result.push(`null`);
+		result.push('null');
 		return result.join('\n');
 	}
 
-	result.push(`{`);
+	result.push('{');
 	for (const [key, value] of Object.entries(obj)) {
 		if (typeof value === 'object' && value !== null) {
 			result.push(`${indent(indentLevel + 1)}${printKey(key)}: ${printObject(value, indentLevel + 1)},`);
@@ -106,9 +106,9 @@ function replaceDynamicRefs(node, anchorName = DEFAULT_ANCHOR) {
 	visit(node, (n, k) => {
 		const v = n[k];
 		if (k === '$dynamicRef' && v === '#' + anchorName) {
-			n['$ref'] = '#';
-			delete n['$dynamicRef'];
-		};
+			n.$ref = '#';
+			delete n.$dynamicRef;
+		}
 	});
 }
 
@@ -117,9 +117,9 @@ function replaceRecursiveRefs(node, anchorName = DEFAULT_ANCHOR) {
 	visit(node, (n, k) => {
 		const v = n[k];
 		if (k === '$recursiveRef') {
-			n['$ref'] = v;
-			delete n['$recursiveRef'];
-		};
+			n.$ref = v;
+			delete n.$recursiveRef;
+		}
 	});
 }
 
@@ -130,7 +130,7 @@ function replaceOldRefs(node, anchorName = DEFAULT_ANCHOR) {
 		if (k === '$ref' && typeof v === 'string' && v.startsWith(anchorName + '/')) {
 			const segments = v.split('#');
 			if (segments.length === 2) {
-				n['$ref'] = `#${segments[1]}`;
+				n.$ref = `#${segments[1]}`;
 			}
 		}
 	});
@@ -149,7 +149,7 @@ function stripDynamicAnchors(node) {
 function collectVocabularies(schema) {
 	const vocabularies = [];
 	const defs = schema.$defs || {};
-	for (const [key, value] of Object.entries(defs)) {
+	for (const [, value] of Object.entries(defs)) {
 		if (value && typeof value === 'object' && !Array.isArray(value) && value.$id && value.$dynamicAnchor === DEFAULT_ANCHOR && value.properties) {
 			vocabularies.push(value);
 		}
@@ -251,4 +251,4 @@ function flattenDraftMetaSchema(original) {
 	}
 
 	return schema;
-}
+}
\ No newline at end of file
diff --git a/build/remove-sourcemap-refs.js b/build/remove-sourcemap-refs.js
index 4c008223..582d408e 100644
--- a/build/remove-sourcemap-refs.js
+++ b/build/remove-sourcemap-refs.js
@@ -3,30 +3,33 @@
  *  Licensed under the MIT License. See License.txt in the project root for license information.
  *--------------------------------------------------------------------------------------------*/
 
-const fs = require('fs');
-const path = require('path');
+import fs from 'node:fs';
+import path from 'node:path';
+import { fileURLToPath } from 'node:url';
+
+const __dirname = path.dirname(fileURLToPath(import.meta.url));
 
 function deleteRefs(dir) {
     const files = fs.readdirSync(dir);
-    for (let file of files) {
+    for (const file of files) {
         const filePath = path.join(dir, file);
         const stat = fs.statSync(filePath);
         if (stat.isDirectory()) {
             deleteRefs(filePath);
         } else if (path.extname(file) === '.js') {
             const content = fs.readFileSync(filePath, 'utf8');
-            const newContent = content.replace(/\/\/\# sourceMappingURL=[^]+.js.map/, '')
+            const newContent = content.replace(/\/\/\# sourceMappingURL=[^]+.js.map/, '');
             if (content.length !== newContent.length) {
                 console.log('remove sourceMappingURL in ' + filePath);
                 fs.writeFileSync(filePath, newContent);
             }
         } else if (path.extname(file) === '.map') {
-            fs.unlinkSync(filePath)
+            fs.unlinkSync(filePath);
             console.log('remove ' + filePath);
         }
     }
 }
 
-let location = path.join(__dirname, '..', 'lib');
+const location = path.join(__dirname, '..', 'lib');
 console.log('process ' + location);
 deleteRefs(location);
\ No newline at end of file
diff --git a/package-lock.json b/package-lock.json
index db59f87b..fdda6fb6 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -1,12 +1,12 @@
 {
   "name": "vscode-json-languageservice",
-  "version": "5.7.2",
+  "version": "6.0.0-next.1",
   "lockfileVersion": 2,
   "requires": true,
   "packages": {
     "": {
       "name": "vscode-json-languageservice",
-      "version": "5.7.2",
+      "version": "6.0.0-next.1",
       "license": "MIT",
       "dependencies": {
         "@vscode/l10n": "^0.0.18",
diff --git a/package.json b/package.json
index de780e43..b17e094b 100644
--- a/package.json
+++ b/package.json
@@ -1,10 +1,15 @@
 {
   "name": "vscode-json-languageservice",
-  "version": "5.7.2",
+  "version": "6.0.0-next.1",
   "description": "Language service for JSON",
-  "main": "./lib/umd/jsonLanguageService.js",
-  "typings": "./lib/umd/jsonLanguageService",
-  "module": "./lib/esm/jsonLanguageService.js",
+  "type": "module",
+  "types": "./lib/esm/jsonLanguageService.d.ts",
+  "exports": {
+    ".": {
+      "types": "./lib/esm/jsonLanguageService.d.ts",
+      "import": "./lib/esm/jsonLanguageService.js"
+    }
+  },
   "author": "Microsoft Corporation",
   "repository": {
     "type": "git",
@@ -31,18 +36,18 @@
     "@vscode/l10n": "^0.0.18"
   },
   "scripts": {
-    "prepack": "npm run clean && npm run compile-esm && npm run test && npm run remove-sourcemap-refs",
+    "prepack": "npm run clean && npm run compile && npm run test && npm run remove-sourcemap-refs",
     "compile": "tsc -p ./src",
-    "compile-esm": "tsc -p ./src/tsconfig.esm.json",
     "clean": "rimraf lib",
+    "bundle-schemas": "node ./build/bundle-schemas.js",
     "remove-sourcemap-refs": "node ./build/remove-sourcemap-refs.js",
     "watch": "tsc -w -p ./src",
     "pretest": "npm run compile",
-    "test": "node --test ./lib/umd/test/**/*.test.js",
+    "test": "node --test ./lib/esm/test/**/*.test.js",
     "posttest": "npm run lint",
     "coverage": "npx nyc -r lcov npm run test",
     "lint": "eslint src/**/*.ts",
     "install-types-next": "npm install vscode-languageserver-types@next -f -S && npm install vscode-languageserver-textdocument@next -f -S",
-    "sample": "npm run compile && node ./lib/umd/example/sample.js"
+    "sample": "npm run compile && node ./lib/esm/example/sample.js"
   }
 }
diff --git a/src/example/sample.ts b/src/example/sample.ts
index b45e4aac..dd2a9925 100644
--- a/src/example/sample.ts
+++ b/src/example/sample.ts
@@ -1,6 +1,6 @@
 
 
-import { getLanguageService, TextDocument } from '../jsonLanguageService';
+import { getLanguageService, TextDocument } from '../jsonLanguageService.js';
 
 async function main() {
     const jsonContentUri = 'foo://server/example.data.json';
diff --git a/src/jsonContributions.ts b/src/jsonContributions.ts
index fe5be120..dfe8c4da 100644
--- a/src/jsonContributions.ts
+++ b/src/jsonContributions.ts
@@ -2,7 +2,7 @@
  *  Copyright (c) Microsoft Corporation. All rights reserved.
  *  Licensed under the MIT License. See License.txt in the project root for license information.
  *--------------------------------------------------------------------------------------------*/
-import { MarkedString, CompletionItem } from './jsonLanguageService';
+import { MarkedString, CompletionItem } from './jsonLanguageService.js';
 
 export interface JSONWorkerContribution {
 	getInfoContribution(uri: string, location: JSONPath): PromiseLike<MarkedString[]>;
diff --git a/src/jsonLanguageService.ts b/src/jsonLanguageService.ts
index 56d3f795..4a0c90df 100644
--- a/src/jsonLanguageService.ts
+++ b/src/jsonLanguageService.ts
@@ -3,18 +3,18 @@
  *  Licensed under the MIT License. See License.txt in the project root for license information.
  *--------------------------------------------------------------------------------------------*/
 
-import { JSONCompletion } from './services/jsonCompletion';
-import { JSONHover } from './services/jsonHover';
-import { JSONValidation } from './services/jsonValidation';
+import { JSONCompletion } from './services/jsonCompletion.js';
+import { JSONHover } from './services/jsonHover.js';
+import { JSONValidation } from './services/jsonValidation.js';
 
-import { JSONDocumentSymbols } from './services/jsonDocumentSymbols';
-import { parse as parseJSON, newJSONDocument } from './parser/jsonParser';
-import { schemaContributions } from './services/configuration';
-import { JSONSchemaService } from './services/jsonSchemaService';
-import { getFoldingRanges } from './services/jsonFolding';
-import { getSelectionRanges } from './services/jsonSelectionRanges';
-import { sort } from './utils/sort';
-import { format } from './utils/format';
+import { JSONDocumentSymbols } from './services/jsonDocumentSymbols.js';
+import { parse as parseJSON, newJSONDocument } from './parser/jsonParser.js';
+import { schemaContributions } from './services/configuration.js';
+import { JSONSchemaService } from './services/jsonSchemaService.js';
+import { getFoldingRanges } from './services/jsonFolding.js';
+import { getSelectionRanges } from './services/jsonSelectionRanges.js';
+import { sort } from './utils/sort.js';
+import { format } from './utils/format.js';
 
 import {
 	ASTNode,
@@ -24,15 +24,15 @@ import {
 	TextDocument,
 	Position, CompletionItem, CompletionList, Hover, Range, SymbolInformation, Diagnostic,
 	TextEdit, FormattingOptions, DocumentSymbol, DefinitionLink, MatchingSchema, JSONLanguageStatus, SortOptions
-} from './jsonLanguageTypes';
-import { findLinks } from './services/jsonLinks';
+} from './jsonLanguageTypes.js';
+import { findLinks } from './services/jsonLinks.js';
 import { DocumentLink } from 'vscode-languageserver-types';
 
 export type JSONDocument = {
 	root: ASTNode | undefined;
 	getNodeFromOffset(offset: number, includeRightBound?: boolean): ASTNode | undefined;
 };
-export * from './jsonLanguageTypes';
+export * from './jsonLanguageTypes.js';
 
 export interface LanguageService {
 	configure(settings: LanguageSettings): void;
diff --git a/src/jsonLanguageTypes.ts b/src/jsonLanguageTypes.ts
index 855fa921..ae32f5e0 100644
--- a/src/jsonLanguageTypes.ts
+++ b/src/jsonLanguageTypes.ts
@@ -3,8 +3,8 @@
  *  Licensed under the MIT License. See License.txt in the project root for license information.
  *--------------------------------------------------------------------------------------------*/
 
-import { JSONWorkerContribution, JSONPath, Segment, CompletionsCollector } from './jsonContributions';
-import { JSONSchema } from './jsonSchema';
+import { JSONWorkerContribution, JSONPath, Segment, CompletionsCollector } from './jsonContributions.js';
+import { JSONSchema } from './jsonSchema.js';
 import {
 	Range, Position, DocumentUri, MarkupContent, MarkupKind,
 	Color, ColorInformation, ColorPresentation,
diff --git a/src/parser/jsonParser.ts b/src/parser/jsonParser.ts
index ebd5f5fe..ad5adb8d 100644
--- a/src/parser/jsonParser.ts
+++ b/src/parser/jsonParser.ts
@@ -4,10 +4,10 @@
  *--------------------------------------------------------------------------------------------*/
 
 import * as Json from 'jsonc-parser';
-import { JSONSchema, JSONSchemaRef } from '../jsonSchema';
-import { isNumber, equals, isBoolean, isString, isDefined, isObject } from '../utils/objects';
-import { extendedRegExp, stringLength } from '../utils/strings';
-import { TextDocument, ASTNode, ObjectASTNode, ArrayASTNode, BooleanASTNode, NumberASTNode, StringASTNode, NullASTNode, PropertyASTNode, JSONPath, ErrorCode, Diagnostic, DiagnosticSeverity, Range, SchemaDraft } from '../jsonLanguageTypes';
+import { JSONSchema, JSONSchemaRef } from '../jsonSchema.js';
+import { isNumber, equals, isBoolean, isString, isDefined, isObject } from '../utils/objects.js';
+import { extendedRegExp, stringLength } from '../utils/strings.js';
+import { TextDocument, ASTNode, ObjectASTNode, ArrayASTNode, BooleanASTNode, NumberASTNode, StringASTNode, NullASTNode, PropertyASTNode, JSONPath, ErrorCode, Diagnostic, DiagnosticSeverity, Range, SchemaDraft } from '../jsonLanguageTypes.js';
 import { URI } from 'vscode-uri';
 
 import * as l10n from '@vscode/l10n';
diff --git a/src/services/configuration.ts b/src/services/configuration.ts
index 6578dba3..c2800dbd 100644
--- a/src/services/configuration.ts
+++ b/src/services/configuration.ts
@@ -3,9 +3,9 @@
  *  Licensed under the MIT License. See License.txt in the project root for license information.
  *--------------------------------------------------------------------------------------------*/
 
-import { ISchemaContributions } from './jsonSchemaService';
-import draft201909Flat from './schemas/draft-2019-09-flat';
-import draft202012Flat from './schemas/draft-2020-12-flat';
+import { ISchemaContributions } from './jsonSchemaService.js';
+import draft201909Flat from './schemas/draft-2019-09-flat.js';
+import draft202012Flat from './schemas/draft-2020-12-flat.js';
 
 import * as l10n from '@vscode/l10n';
 
diff --git a/src/services/jsonCompletion.ts b/src/services/jsonCompletion.ts
index 61946ccd..458ae3be 100644
--- a/src/services/jsonCompletion.ts
+++ b/src/services/jsonCompletion.ts
@@ -3,20 +3,20 @@
  *  Licensed under the MIT License. See License.txt in the project root for license information.
  *--------------------------------------------------------------------------------------------*/
 
-import * as Parser from '../parser/jsonParser';
+import * as Parser from '../parser/jsonParser.js';
 import * as Json from 'jsonc-parser';
-import * as SchemaService from './jsonSchemaService';
-import { JSONSchema, JSONSchemaRef } from '../jsonSchema';
-import { JSONWorkerContribution, CompletionsCollector, JSONCompletionItem } from '../jsonContributions';
-import { stringifyObject } from '../utils/json';
-import { endsWith, extendedRegExp } from '../utils/strings';
-import { isDefined } from '../utils/objects';
+import * as SchemaService from './jsonSchemaService.js';
+import { JSONSchema, JSONSchemaRef } from '../jsonSchema.js';
+import { JSONWorkerContribution, CompletionsCollector, JSONCompletionItem } from '../jsonContributions.js';
+import { stringifyObject } from '../utils/json.js';
+import { endsWith, extendedRegExp } from '../utils/strings.js';
+import { isDefined } from '../utils/objects.js';
 import {
 	PromiseConstructor,
 	ASTNode, ObjectASTNode, ArrayASTNode, PropertyASTNode, ClientCapabilities,
 	TextDocument,
 	CompletionItem, CompletionItemKind, CompletionList, Position, Range, TextEdit, InsertTextFormat, MarkupContent, MarkupKind
-} from '../jsonLanguageTypes';
+} from '../jsonLanguageTypes.js';
 
 import * as l10n from '@vscode/l10n';
 
diff --git a/src/services/jsonDocumentSymbols.ts b/src/services/jsonDocumentSymbols.ts
index e3b752ca..74941241 100644
--- a/src/services/jsonDocumentSymbols.ts
+++ b/src/services/jsonDocumentSymbols.ts
@@ -3,17 +3,17 @@
  *  Licensed under the MIT License. See License.txt in the project root for license information.
  *--------------------------------------------------------------------------------------------*/
 
-import * as Parser from '../parser/jsonParser';
-import * as Strings from '../utils/strings';
-import { colorFromHex } from '../utils/colors';
+import * as Parser from '../parser/jsonParser.js';
+import * as Strings from '../utils/strings.js';
+import { colorFromHex } from '../utils/colors.js';
 import * as l10n from '@vscode/l10n';
 
 import {
 	TextDocument, ColorInformation, ColorPresentation, Color, ASTNode, PropertyASTNode, DocumentSymbolsContext, Range, TextEdit,
 	SymbolInformation, SymbolKind, DocumentSymbol, Location
-} from "../jsonLanguageTypes";
+} from "../jsonLanguageTypes.js";
 
-import { IJSONSchemaService } from "./jsonSchemaService";
+import { IJSONSchemaService } from "./jsonSchemaService.js";
 
 export class JSONDocumentSymbols {
 
diff --git a/src/services/jsonFolding.ts b/src/services/jsonFolding.ts
index d04afc13..5460339e 100644
--- a/src/services/jsonFolding.ts
+++ b/src/services/jsonFolding.ts
@@ -4,7 +4,7 @@
  *--------------------------------------------------------------------------------------------*/
 
 import { createScanner, SyntaxKind, ScanError } from 'jsonc-parser';
-import { TextDocument, FoldingRangeKind, FoldingRange, FoldingRangesContext, Position } from '../jsonLanguageTypes';
+import { TextDocument, FoldingRangeKind, FoldingRange, FoldingRangesContext, Position } from '../jsonLanguageTypes.js';
 
 export function getFoldingRanges(document: TextDocument, context?: FoldingRangesContext): FoldingRange[] {
 	const ranges: FoldingRange[] = [];
diff --git a/src/services/jsonHover.ts b/src/services/jsonHover.ts
index 381d085e..c29d7fc1 100644
--- a/src/services/jsonHover.ts
+++ b/src/services/jsonHover.ts
@@ -3,10 +3,10 @@
  *  Licensed under the MIT License. See License.txt in the project root for license information.
  *--------------------------------------------------------------------------------------------*/
 
-import * as Parser from '../parser/jsonParser';
-import * as SchemaService from './jsonSchemaService';
-import { JSONWorkerContribution } from '../jsonContributions';
-import { TextDocument, PromiseConstructor, Position, Range, Hover, MarkedString } from '../jsonLanguageTypes';
+import * as Parser from '../parser/jsonParser.js';
+import * as SchemaService from './jsonSchemaService.js';
+import { JSONWorkerContribution } from '../jsonContributions.js';
+import { TextDocument, PromiseConstructor, Position, Range, Hover, MarkedString } from '../jsonLanguageTypes.js';
 
 export class JSONHover {
 
diff --git a/src/services/jsonLinks.ts b/src/services/jsonLinks.ts
index 51d29364..fd47428d 100644
--- a/src/services/jsonLinks.ts
+++ b/src/services/jsonLinks.ts
@@ -4,8 +4,8 @@
  *--------------------------------------------------------------------------------------------*/
 
 import { DocumentLink } from 'vscode-languageserver-types';
-import { TextDocument, ASTNode, PropertyASTNode, Range } from '../jsonLanguageTypes';
-import { JSONDocument } from '../parser/jsonParser';
+import { TextDocument, ASTNode, PropertyASTNode, Range } from '../jsonLanguageTypes.js';
+import { JSONDocument } from '../parser/jsonParser.js';
 
 export function findLinks(document: TextDocument, doc: JSONDocument): PromiseLike<DocumentLink[]> {
 	const links: DocumentLink[] = [];
diff --git a/src/services/jsonSchemaService.ts b/src/services/jsonSchemaService.ts
index 1b753a67..33010d79 100644
--- a/src/services/jsonSchemaService.ts
+++ b/src/services/jsonSchemaService.ts
@@ -4,15 +4,15 @@
  *--------------------------------------------------------------------------------------------*/
 
 import * as Json from 'jsonc-parser';
-import { JSONSchema, JSONSchemaMap, JSONSchemaRef } from '../jsonSchema';
+import { JSONSchema, JSONSchemaMap, JSONSchemaRef } from '../jsonSchema.js';
 import { URI } from 'vscode-uri';
-import * as Strings from '../utils/strings';
-import { asSchema, getSchemaDraftFromId, JSONDocument, normalizeId } from '../parser/jsonParser';
-import { SchemaRequestService, WorkspaceContextService, PromiseConstructor, MatchingSchema, TextDocument, SchemaConfiguration, SchemaDraft, ErrorCode } from '../jsonLanguageTypes';
+import * as Strings from '../utils/strings.js';
+import { asSchema, getSchemaDraftFromId, JSONDocument, normalizeId } from '../parser/jsonParser.js';
+import { SchemaRequestService, WorkspaceContextService, PromiseConstructor, MatchingSchema, TextDocument, SchemaConfiguration, SchemaDraft, ErrorCode } from '../jsonLanguageTypes.js';
 
 import * as l10n from '@vscode/l10n';
-import { createRegex } from '../utils/glob';
-import { isObject, isString } from '../utils/objects';
+import { createRegex } from '../utils/glob.js';
+import { isObject, isString } from '../utils/objects.js';
 import { DiagnosticRelatedInformation, Range } from 'vscode-languageserver-types';
 
 export interface IJSONSchemaService {
diff --git a/src/services/jsonSelectionRanges.ts b/src/services/jsonSelectionRanges.ts
index 277105a8..7a1f19ba 100644
--- a/src/services/jsonSelectionRanges.ts
+++ b/src/services/jsonSelectionRanges.ts
@@ -3,9 +3,9 @@
  *  Licensed under the MIT License. See License.txt in the project root for license information.
  *--------------------------------------------------------------------------------------------*/
 
-import { Range, Position, SelectionRange, TextDocument } from '../jsonLanguageTypes';
+import { Range, Position, SelectionRange, TextDocument } from '../jsonLanguageTypes.js';
 
-import { JSONDocument } from '../parser/jsonParser';
+import { JSONDocument } from '../parser/jsonParser.js';
 import { SyntaxKind, createScanner } from 'jsonc-parser';
 
 export function getSelectionRanges(document: TextDocument, positions: Position[], doc: JSONDocument): SelectionRange[] {
diff --git a/src/services/jsonValidation.ts b/src/services/jsonValidation.ts
index f1f49a67..3bca6fb9 100644
--- a/src/services/jsonValidation.ts
+++ b/src/services/jsonValidation.ts
@@ -3,13 +3,13 @@
  *  Licensed under the MIT License. See License.txt in the project root for license information.
  *--------------------------------------------------------------------------------------------*/
 
-import { JSONSchemaService, ResolvedSchema } from './jsonSchemaService';
-import { JSONDocument } from '../parser/jsonParser';
+import { JSONSchemaService, ResolvedSchema } from './jsonSchemaService.js';
+import { JSONDocument } from '../parser/jsonParser.js';
 
-import { TextDocument, ErrorCode, PromiseConstructor, LanguageSettings, DocumentLanguageSettings, SeverityLevel, Diagnostic, DiagnosticSeverity, Range, JSONLanguageStatus } from '../jsonLanguageTypes';
+import { TextDocument, ErrorCode, PromiseConstructor, LanguageSettings, DocumentLanguageSettings, SeverityLevel, Diagnostic, DiagnosticSeverity, Range, JSONLanguageStatus } from '../jsonLanguageTypes.js';
 import * as l10n from '@vscode/l10n';
-import { JSONSchemaRef, JSONSchema } from '../jsonSchema';
-import { isBoolean } from '../utils/objects';
+import { JSONSchemaRef, JSONSchema } from '../jsonSchema.js';
+import { isBoolean } from '../utils/objects.js';
 import { DiagnosticRelatedInformation } from 'vscode-languageserver-types';
 
 export class JSONValidation {
diff --git a/src/test/completion.test.ts b/src/test/completion.test.ts
index 1ed8ec73..c4930ca3 100644
--- a/src/test/completion.test.ts
+++ b/src/test/completion.test.ts
@@ -6,8 +6,8 @@
 import * as assert from 'assert';
 import { suite, test } from 'node:test';
 
-import { getLanguageService, JSONSchema, TextDocument, ClientCapabilities, CompletionList, CompletionItemKind, Position, MarkupContent, TextEdit } from '../jsonLanguageService';
-import { repeat } from '../utils/strings';
+import { getLanguageService, JSONSchema, TextDocument, ClientCapabilities, CompletionList, CompletionItemKind, Position, MarkupContent, TextEdit } from '../jsonLanguageService.js';
+import { repeat } from '../utils/strings.js';
 import { CompletionItemLabelDetails } from 'vscode-languageserver-types';
 
 const applyEdits = TextDocument.applyEdits;
diff --git a/src/test/documentSymbols.test.ts b/src/test/documentSymbols.test.ts
index 8e8a01de..80ea00a2 100644
--- a/src/test/documentSymbols.test.ts
+++ b/src/test/documentSymbols.test.ts
@@ -5,14 +5,14 @@
 
 import * as assert from 'assert';
 import { suite, test } from 'node:test';
-import * as JsonSchema from '../jsonSchema';
+import * as JsonSchema from '../jsonSchema.js';
 
 import {
 	getLanguageService,
 	ClientCapabilities, DocumentSymbolsContext,
 	TextDocument, Color, SymbolInformation, SymbolKind, Range, Position, TextEdit, DocumentSymbol
-} from "../jsonLanguageService";
-import { colorFrom256RGB } from '../utils/colors';
+} from "../jsonLanguageService.js";
+import { colorFrom256RGB } from '../utils/colors.js';
 
 suite('JSON Document Symbols', () => {
 
diff --git a/src/test/folding.test.ts b/src/test/folding.test.ts
index 02afaf33..c10092f6 100644
--- a/src/test/folding.test.ts
+++ b/src/test/folding.test.ts
@@ -5,7 +5,7 @@
 
 import { suite, test } from 'node:test';
 import * as assert from 'assert';
-import { TextDocument, getLanguageService } from '../jsonLanguageService';
+import { TextDocument, getLanguageService } from '../jsonLanguageService.js';
 
 interface ExpectedIndentRange {
 	startLine: number;
diff --git a/src/test/formatter.test.ts b/src/test/formatter.test.ts
index bbff1570..3a58f16d 100644
--- a/src/test/formatter.test.ts
+++ b/src/test/formatter.test.ts
@@ -3,7 +3,7 @@
  *  Licensed under the MIT License. See License.txt in the project root for license information.
  *--------------------------------------------------------------------------------------------*/
 
-import { getLanguageService, ClientCapabilities, Range, TextDocument } from '../jsonLanguageService';
+import { getLanguageService, ClientCapabilities, Range, TextDocument } from '../jsonLanguageService.js';
 import * as assert from 'assert';
 import { suite, test } from 'node:test';
 
diff --git a/src/test/glob.test.ts b/src/test/glob.test.ts
index 5503aea5..1ee3b12e 100644
--- a/src/test/glob.test.ts
+++ b/src/test/glob.test.ts
@@ -5,7 +5,7 @@
 
 import * as assert from 'assert';
 import { suite, test } from 'node:test';
-import { createRegex } from '../utils/glob';
+import { createRegex } from '../utils/glob.js';
 
 
 suite('Glob', () => {
@@ -61,10 +61,10 @@ suite('Glob', () => {
             const regex = createRegex(pattern, { extended: true, globstar: true });
             const result = regex.test(input);
             if (result !== expected) {
-                assert(false, `pattern: ${pattern}, regex: ${regex.source}, input: ${input}, should match ${expected}`);
+                assert.fail(`pattern: ${pattern}, regex: ${regex.source}, input: ${input}, should match ${expected}`);
             }
         } catch (e) {
-            assert(false, `pattern: ${pattern}, input: ${input}, should match ${expected}`);
+            assert.fail(`pattern: ${pattern}, input: ${input}, should match ${expected}`);
         }
     }
 
diff --git a/src/test/hover.test.ts b/src/test/hover.test.ts
index 8e67b0d0..3e663fd1 100644
--- a/src/test/hover.test.ts
+++ b/src/test/hover.test.ts
@@ -6,7 +6,7 @@
 import * as assert from 'assert';
 import { suite, test } from 'node:test';
 
-import { Hover, Position, TextDocument, getLanguageService, JSONSchema, LanguageServiceParams } from '../jsonLanguageService';
+import { Hover, Position, TextDocument, getLanguageService, JSONSchema, LanguageServiceParams } from '../jsonLanguageService.js';
 
 suite('JSON Hover', () => {
 
@@ -24,7 +24,7 @@ suite('JSON Hover', () => {
 		const document = TextDocument.create(uri, 'json', 0, value);
 		const jsonDoc = service.parseJSONDocument(document);
 		const hover = await service.doHover(document, position, jsonDoc);
-		assert(hover, 'expected hover to be returned');
+		assert.ok(hover, 'expected hover to be returned');
 		return hover;
 	}
 
diff --git a/src/test/jsonSchemaTestSuite.test.ts b/src/test/jsonSchemaTestSuite.test.ts
index 94c27d7c..5f2d4263 100644
--- a/src/test/jsonSchemaTestSuite.test.ts
+++ b/src/test/jsonSchemaTestSuite.test.ts
@@ -5,13 +5,14 @@
 
 import * as assert from 'assert';
 import { suite, test, after } from 'node:test';
-import * as Parser from '../parser/jsonParser';
+import * as Parser from '../parser/jsonParser.js';
 import * as fs from 'fs';
 import * as url from 'url';
 import * as path from 'path';
-import { getLanguageService, SchemaDraft, TextDocument } from '../jsonLanguageService';
+import { getLanguageService, SchemaDraft, TextDocument } from '../jsonLanguageService.js';
 import { URI } from 'vscode-uri';
 
+const __dirname = path.dirname(url.fileURLToPath(import.meta.url));
 const testsPath = path.join(__dirname, "../../../node_modules/json-schema-test-suite/tests");
 
 const drafts = [
diff --git a/src/test/links.test.ts b/src/test/links.test.ts
index b788afa9..49df7cc8 100644
--- a/src/test/links.test.ts
+++ b/src/test/links.test.ts
@@ -6,7 +6,7 @@
 import * as assert from 'assert';
 import { suite, test } from 'node:test';
 
-import { getLanguageService, Range, TextDocument, ClientCapabilities } from '../jsonLanguageService';
+import { getLanguageService, Range, TextDocument, ClientCapabilities } from '../jsonLanguageService.js';
 
 suite('JSON Find Links', () => {
 	const testFindLinksFor = function (value: string, expected: {offset: number, length: number, target: number} | null): PromiseLike<void> {
diff --git a/src/test/parser.test.ts b/src/test/parser.test.ts
index 87152d8c..06cba385 100644
--- a/src/test/parser.test.ts
+++ b/src/test/parser.test.ts
@@ -5,8 +5,8 @@
 
 import * as assert from 'assert';
 import { suite, test } from 'node:test';
-import { getNodePath, getNodeValue, JSONDocument } from '../parser/jsonParser';
-import { TextDocument, Range, ErrorCode, ASTNode, ObjectASTNode, getLanguageService, JSONSchema, SchemaDraft } from '../jsonLanguageService';
+import { getNodePath, getNodeValue, JSONDocument } from '../parser/jsonParser.js';
+import { TextDocument, Range, ErrorCode, ASTNode, ObjectASTNode, getLanguageService, JSONSchema, SchemaDraft } from '../jsonLanguageService.js';
 import { DiagnosticSeverity } from 'vscode-languageserver-types';
 
 suite('JSON Parser', () => {
diff --git a/src/test/schema.test.ts b/src/test/schema.test.ts
index 41f8a6d6..db790fe2 100644
--- a/src/test/schema.test.ts
+++ b/src/test/schema.test.ts
@@ -5,13 +5,15 @@
 
 import * as assert from 'assert';
 import { suite, test } from 'node:test';
-import * as SchemaService from '../services/jsonSchemaService';
-import * as Parser from '../parser/jsonParser';
+import * as SchemaService from '../services/jsonSchemaService.js';
+import * as Parser from '../parser/jsonParser.js';
 import { promises as fs } from 'fs';
 import * as url from 'url';
 import * as path from 'path';
-import { getLanguageService, JSONSchema, SchemaRequestService, TextDocument, MatchingSchema, LanguageService } from '../jsonLanguageService';
-import { DiagnosticSeverity, ErrorCode, Range, SchemaConfiguration } from '../jsonLanguageTypes';
+import { getLanguageService, JSONSchema, SchemaRequestService, TextDocument, MatchingSchema, LanguageService } from '../jsonLanguageService.js';
+import { DiagnosticSeverity, ErrorCode, Range, SchemaConfiguration } from '../jsonLanguageTypes.js';
+
+const __dirname = path.dirname(url.fileURLToPath(import.meta.url));
 
 function toDocument(text: string, config?: Parser.JSONDocumentConfig, uri = 'foo://bar/file.json'): { textDoc: TextDocument, jsonDoc: Parser.JSONDocument } {
 
diff --git a/src/test/selectionRanges.test.ts b/src/test/selectionRanges.test.ts
index ce20d180..b58408be 100644
--- a/src/test/selectionRanges.test.ts
+++ b/src/test/selectionRanges.test.ts
@@ -5,7 +5,7 @@
 
 import { suite, test } from 'node:test';
 import * as assert from 'assert';
-import { getLanguageService, TextDocument } from '../jsonLanguageService';
+import { getLanguageService, TextDocument } from '../jsonLanguageService.js';
 import { SelectionRange } from 'vscode-languageserver-types';
 
 function assertRanges(content: string, expected: (number | string)[][]): void {
diff --git a/src/test/sort.test.ts b/src/test/sort.test.ts
index abc8d942..6ab66e1c 100644
--- a/src/test/sort.test.ts
+++ b/src/test/sort.test.ts
@@ -1,5 +1,5 @@
 
-import { getLanguageService, ClientCapabilities, TextDocument, SortOptions } from '../jsonLanguageService';
+import { getLanguageService, ClientCapabilities, TextDocument, SortOptions } from '../jsonLanguageService.js';
 import * as assert from 'assert';
 import { suite, test } from 'node:test';
 
diff --git a/src/test/stringify.test.ts b/src/test/stringify.test.ts
index f54d3689..f6e87996 100644
--- a/src/test/stringify.test.ts
+++ b/src/test/stringify.test.ts
@@ -3,7 +3,7 @@
  *  Licensed under the MIT License. See License.txt in the project root for license information.
  *--------------------------------------------------------------------------------------------*/
 
-import { stringifyObject } from '../utils/json';
+import { stringifyObject } from '../utils/json.js';
 import * as assert from 'assert';
 import { suite, test } from 'node:test';
 
diff --git a/src/tsconfig.esm.json b/src/tsconfig.esm.json
index 387739c8..c9011ba2 100644
--- a/src/tsconfig.esm.json
+++ b/src/tsconfig.esm.json
@@ -1,14 +1,3 @@
 {
-	"compilerOptions": {
-		"target": "es2020",
-		"module": "es6",
-		"moduleResolution": "node",
-		"sourceMap": true,
-		"declaration": true,
-		"stripInternal": true,
-		"outDir": "../lib/esm",
-		"lib": [
-			"es2020"
-		]
-	}
+	"extends": "./tsconfig.json"
 }
\ No newline at end of file
diff --git a/src/tsconfig.json b/src/tsconfig.json
index e903a2bf..c3853271 100644
--- a/src/tsconfig.json
+++ b/src/tsconfig.json
@@ -1,12 +1,12 @@
 {
 	"compilerOptions": {
 		"target": "es2020",
-		"module": "umd",
-		"moduleResolution": "node",
+		"module": "NodeNext",
+		"moduleResolution": "NodeNext",
 		"sourceMap": true,
 		"declaration": true,
 		"stripInternal": true,
-		"outDir": "../lib/umd",
+		"outDir": "../lib/esm",
 		"lib": [
 			"es2020"
 		],
diff --git a/src/utils/colors.ts b/src/utils/colors.ts
index 1d710601..3513930f 100644
--- a/src/utils/colors.ts
+++ b/src/utils/colors.ts
@@ -3,7 +3,7 @@
  *  Licensed under the MIT License. See License.txt in the project root for license information.
  *--------------------------------------------------------------------------------------------*/
 
-import { Color } from "../jsonLanguageTypes";
+import { Color } from "../jsonLanguageTypes.js";
 
 const Digit0 = 48;
 const Digit9 = 57;
diff --git a/src/utils/format.ts b/src/utils/format.ts
index 14f4d94c..7cf6b071 100644
--- a/src/utils/format.ts
+++ b/src/utils/format.ts
@@ -1,5 +1,5 @@
 import { format as formatJSON, Range as JSONCRange } from 'jsonc-parser'; 
-import { TextDocument, Range, TextEdit, FormattingOptions } from '../jsonLanguageTypes';
+import { TextDocument, Range, TextEdit, FormattingOptions } from '../jsonLanguageTypes.js';
 
 export function format(documentToFormat: TextDocument, formattingOptions?: FormattingOptions, formattingRange?: Range | undefined): TextEdit[] {
 	let range: JSONCRange | undefined = undefined;
diff --git a/src/utils/sort.ts b/src/utils/sort.ts
index 2f3d539d..9dd8c57c 100644
--- a/src/utils/sort.ts
+++ b/src/utils/sort.ts
@@ -4,9 +4,9 @@
 *--------------------------------------------------------------------------------------------*/
 
 import { createScanner, SyntaxKind, JSONScanner } from 'jsonc-parser';
-import { TextDocument, TextEdit, FormattingOptions, Position, Range, TextDocumentContentChangeEvent, SortOptions } from '../jsonLanguageTypes';
-import { format } from './format';
-import { PropertyTree, Container } from './propertyTree';
+import { TextDocument, TextEdit, FormattingOptions, Position, Range, TextDocumentContentChangeEvent, SortOptions } from '../jsonLanguageTypes.js';
+import { format } from './format.js';
+import { PropertyTree, Container } from './propertyTree.js';
 
 export function sort(documentToSort: TextDocument, formattingOptions: SortOptions): TextEdit[] {
     const options: FormattingOptions = {