diff --git a/package.json b/package.json
index 5d63c2b8..9b8d8cfd 100644
--- a/package.json
+++ b/package.json
@@ -355,7 +355,13 @@
         "xml.symbols.showReferencedGrammars": {
           "type": "boolean",
           "default": true,
-          "markdownDescription": "Show referenced grammars in the Outline. Default is `true.",
+          "markdownDescription": "Show referenced grammars in the Outline. Default is `true`.",
+          "scope": "window"
+        },
+        "xml.extension.jars": {
+          "type": "array",
+          "default": [],
+          "markdownDescription": "An array of paths to JARs that should be contributed to the LemMinX classpath. This is intended to be used as a tool for developing extensions to vscode-xml.",
           "scope": "window"
         }
       }
diff --git a/src/extension.ts b/src/extension.ts
index 207e2199..8bdef9d1 100644
--- a/src/extension.ts
+++ b/src/extension.ts
@@ -18,7 +18,7 @@ import * as path from 'path';
 import * as os from 'os';
 import { activateTagClosing, AutoCloseResult } from './tagClosing';
 import { Commands } from './commands';
-import { onConfigurationChange, subscribeJDKChangeConfiguration } from './settings';
+import { getXMLConfiguration, onConfigurationChange, subscribeJDKChangeConfiguration } from './settings';
 import { collectXmlJavaExtensions, onExtensionChange } from './plugin';
 import { markdownPreviewProvider } from "./markdownPreviewProvider";
 
@@ -203,7 +203,7 @@ export function activate(context: ExtensionContext) {
       }
     }
 
-    let serverOptions = prepareExecutable(requirements, collectXmlJavaExtensions(extensions.all), context);
+    let serverOptions = prepareExecutable(requirements, collectXmlJavaExtensions(extensions.all, getXMLConfiguration().get("extension.jars", [])), context);
     languageClient = new LanguageClient('xml', 'XML Support', serverOptions, clientOptions);
     let toDispose = context.subscriptions;
     let disposable = languageClient.start();
@@ -245,7 +245,7 @@ export function activate(context: ExtensionContext) {
 
       if (extensions.onDidChange) {// Theia doesn't support this API yet
         context.subscriptions.push(extensions.onDidChange(() => {
-          onExtensionChange(extensions.all);
+          onExtensionChange(extensions.all, getXMLConfiguration().get("extension.jars", []));
         }));
       }
 
diff --git a/src/plugin.ts b/src/plugin.ts
index d7bdc7b5..9e9e9f00 100644
--- a/src/plugin.ts
+++ b/src/plugin.ts
@@ -7,7 +7,7 @@ const glob = require('glob');
 
 let existingExtensions: Array<string>;
 
-export function collectXmlJavaExtensions(extensions: readonly vscode.Extension<any>[]): string[] {
+export function collectXmlJavaExtensions(extensions: readonly vscode.Extension<any>[], jars: string[]): string[] {
 	const result = [];
 	if (extensions && extensions.length) {
 		for (const extension of extensions) {
@@ -22,17 +22,20 @@ export function collectXmlJavaExtensions(extensions: readonly vscode.Extension<a
 			}
 		}
 	}
+	for (const extension of jars) {
+		result.push(...glob.sync(extension));
+	}
 	// Make a copy of extensions:
 	existingExtensions = result.slice();
 	return result;
 }
 
-export function onExtensionChange(extensions: readonly vscode.Extension<any>[]) {
+export function onExtensionChange(extensions: readonly vscode.Extension<any>[], jars: string[]) {
 	if (!existingExtensions) {
 		return;
 	}
 	const oldExtensions = new Set(existingExtensions.slice());
-	const newExtensions = collectXmlJavaExtensions(extensions);
+	const newExtensions = collectXmlJavaExtensions(extensions, jars);
 	let hasChanged = ( oldExtensions.size !== newExtensions.length);
 	if (!hasChanged) {
 		for (const newExtension of newExtensions) {