diff --git a/extensions/vscode-api-tests/src/singlefolder-tests/env.test.ts b/extensions/vscode-api-tests/src/singlefolder-tests/env.test.ts
index b0dfa3e1145..4189615c09e 100644
--- a/extensions/vscode-api-tests/src/singlefolder-tests/env.test.ts
+++ b/extensions/vscode-api-tests/src/singlefolder-tests/env.test.ts
@@ -4,7 +4,7 @@
  *--------------------------------------------------------------------------------------------*/
 
 import * as assert from 'assert';
-import { env, extensions, ExtensionKind } from 'vscode';
+import { env, extensions, ExtensionKind, UIKind } from 'vscode';
 
 suite('env-namespace', () => {
 
@@ -44,4 +44,9 @@ suite('env-namespace', () => {
 			assert.fail();
 		}
 	});
+
+	test('env.uiKind', function () {
+		const kind = env.uiKind;
+		assert.equal(kind, UIKind.Desktop);
+	});
 });
diff --git a/src/vs/vscode.proposed.d.ts b/src/vs/vscode.proposed.d.ts
index 51fc6a2a958..2edbc6a4220 100644
--- a/src/vs/vscode.proposed.d.ts
+++ b/src/vs/vscode.proposed.d.ts
@@ -1011,6 +1011,36 @@ declare module 'vscode' {
 
 	//#endregion
 
+	// #region Ben - UIKind
+
+	/**
+	 * Possible kinds of UI that can use extensions.
+	 */
+	export enum UIKind {
+
+		/**
+		 * Extensions are accessed from a desktop application.
+		 */
+		Desktop = 1,
+
+		/**
+		 * Extensions are accessed from a web browser.
+		 */
+		Web = 2
+	}
+
+	export namespace env {
+
+		/**
+		 * The UI kind property indicates from which UI extensions
+		 * are accessed from. For example, extensions could be accessed
+		 * from a desktop application or a web browser.
+		 */
+		export const uiKind: UIKind;
+	}
+
+	//#endregion
+
 	//#region Custom editors, mjbvz
 
 	export enum WebviewEditorState {
diff --git a/src/vs/workbench/api/common/extHost.api.impl.ts b/src/vs/workbench/api/common/extHost.api.impl.ts
index 0fd949cb503..417b85c2883 100644
--- a/src/vs/workbench/api/common/extHost.api.impl.ts
+++ b/src/vs/workbench/api/common/extHost.api.impl.ts
@@ -15,7 +15,7 @@ import { OverviewRulerLane } from 'vs/editor/common/model';
 import * as languageConfiguration from 'vs/editor/common/modes/languageConfiguration';
 import { score } from 'vs/editor/common/modes/languageSelector';
 import * as files from 'vs/platform/files/common/files';
-import { ExtHostContext, MainContext, ExtHostLogServiceShape } from 'vs/workbench/api/common/extHost.protocol';
+import { ExtHostContext, MainContext, ExtHostLogServiceShape, UIKind } from 'vs/workbench/api/common/extHost.protocol';
 import { ExtHostApiCommands } from 'vs/workbench/api/common/extHostApiCommands';
 import { ExtHostClipboard } from 'vs/workbench/api/common/extHostClipboard';
 import { IExtHostCommands } from 'vs/workbench/api/common/extHostCommands';
@@ -250,6 +250,10 @@ export function createApiFactoryAndRegisterActors(accessor: ServicesAccessor): I
 			},
 			get remoteName() {
 				return getRemoteName(initData.remote.authority);
+			},
+			get uiKind() {
+				checkProposedApiEnabled(extension);
+				return initData.uiKind;
 			}
 		};
 		if (!initData.environment.extensionTestsLocationURI) {
@@ -898,6 +902,7 @@ export function createApiFactoryAndRegisterActors(accessor: ServicesAccessor): I
 			CallHierarchyItem: extHostTypes.CallHierarchyItem,
 			Decoration: extHostTypes.Decoration,
 			WebviewEditorState: extHostTypes.WebviewEditorState,
+			UIKind: UIKind
 		};
 	};
 }
diff --git a/src/vs/workbench/api/common/extHost.protocol.ts b/src/vs/workbench/api/common/extHost.protocol.ts
index 2067cef3de7..b7bddc60c4d 100644
--- a/src/vs/workbench/api/common/extHost.protocol.ts
+++ b/src/vs/workbench/api/common/extHost.protocol.ts
@@ -87,6 +87,7 @@ export interface IInitData {
 	logsLocation: URI;
 	autoStart: boolean;
 	remote: { isRemote: boolean; authority: string | undefined; };
+	uiKind: UIKind;
 }
 
 export interface IConfigurationInitData extends IConfigurationData {
@@ -105,6 +106,11 @@ export interface IExtHostContext extends IRPCProtocol {
 export interface IMainContext extends IRPCProtocol {
 }
 
+export enum UIKind {
+	Desktop = 1,
+	Web = 2
+}
+
 // --- main thread
 
 export interface MainThreadClipboardShape extends IDisposable {
diff --git a/src/vs/workbench/services/extensions/browser/webWorkerExtensionHostStarter.ts b/src/vs/workbench/services/extensions/browser/webWorkerExtensionHostStarter.ts
index cfd34eeed8d..268ae15a11e 100644
--- a/src/vs/workbench/services/extensions/browser/webWorkerExtensionHostStarter.ts
+++ b/src/vs/workbench/services/extensions/browser/webWorkerExtensionHostStarter.ts
@@ -9,7 +9,7 @@ import { DisposableStore, toDisposable } from 'vs/base/common/lifecycle';
 import { IMessagePassingProtocol } from 'vs/base/parts/ipc/common/ipc';
 import { VSBuffer } from 'vs/base/common/buffer';
 import { createMessageOfType, MessageType, isMessageOfType } from 'vs/workbench/services/extensions/common/extensionHostProtocol';
-import { IInitData } from 'vs/workbench/api/common/extHost.protocol';
+import { IInitData, UIKind } from 'vs/workbench/api/common/extHost.protocol';
 import { ITelemetryService } from 'vs/platform/telemetry/common/telemetry';
 import { IWorkspaceContextService, WorkbenchState } from 'vs/platform/workspace/common/workspace';
 import { ILabelService } from 'vs/platform/label/common/label';
@@ -150,6 +150,7 @@ export class WebWorkerExtensionHostStarter implements IExtensionHostStarter {
 				authority: this._environmentService.configuration.remoteAuthority,
 				isRemote: false
 			},
+			uiKind: platform.isWeb ? UIKind.Web : UIKind.Desktop
 		};
 	}
 }
diff --git a/src/vs/workbench/services/extensions/common/remoteExtensionHostClient.ts b/src/vs/workbench/services/extensions/common/remoteExtensionHostClient.ts
index bcb46463c2c..73d7b53109a 100644
--- a/src/vs/workbench/services/extensions/common/remoteExtensionHostClient.ts
+++ b/src/vs/workbench/services/extensions/common/remoteExtensionHostClient.ts
@@ -11,7 +11,7 @@ import { ILogService } from 'vs/platform/log/common/log';
 import { connectRemoteAgentExtensionHost, IRemoteExtensionHostStartParams, IConnectionOptions, ISocketFactory } from 'vs/platform/remote/common/remoteAgentConnection';
 import { ITelemetryService } from 'vs/platform/telemetry/common/telemetry';
 import { IWorkspaceContextService, WorkbenchState } from 'vs/platform/workspace/common/workspace';
-import { IInitData } from 'vs/workbench/api/common/extHost.protocol';
+import { IInitData, UIKind } from 'vs/workbench/api/common/extHost.protocol';
 import { MessageType, createMessageOfType, isMessageOfType } from 'vs/workbench/services/extensions/common/extensionHostProtocol';
 import { IExtensionHostStarter } from 'vs/workbench/services/extensions/common/extensions';
 import { parseExtensionDevOptions } from 'vs/workbench/services/extensions/common/extensionDevOptions';
@@ -215,6 +215,7 @@ export class RemoteExtensionHostClient extends Disposable implements IExtensionH
 				logLevel: this._logService.getLevel(),
 				logsLocation: remoteExtensionHostData.extensionHostLogsPath,
 				autoStart: true,
+				uiKind: platform.isWeb ? UIKind.Web : UIKind.Desktop
 			};
 			return r;
 		});
diff --git a/src/vs/workbench/services/extensions/electron-browser/extensionHost.ts b/src/vs/workbench/services/extensions/electron-browser/extensionHost.ts
index 0ed2188509d..ef779db4673 100644
--- a/src/vs/workbench/services/extensions/electron-browser/extensionHost.ts
+++ b/src/vs/workbench/services/extensions/electron-browser/extensionHost.ts
@@ -29,7 +29,7 @@ import { INotificationService, Severity } from 'vs/platform/notification/common/
 import { ITelemetryService } from 'vs/platform/telemetry/common/telemetry';
 import { IWindowService, IWindowsService } from 'vs/platform/windows/common/windows';
 import { IWorkspaceContextService, WorkbenchState } from 'vs/platform/workspace/common/workspace';
-import { IInitData } from 'vs/workbench/api/common/extHost.protocol';
+import { IInitData, UIKind } from 'vs/workbench/api/common/extHost.protocol';
 import { MessageType, createMessageOfType, isMessageOfType } from 'vs/workbench/services/extensions/common/extensionHostProtocol';
 import { withNullAsUndefined } from 'vs/base/common/types';
 import { IExtensionDescription } from 'vs/platform/extensions/common/extensions';
@@ -420,7 +420,8 @@ export class ExtensionHostProcessWorker implements IExtensionHostStarter {
 					telemetryInfo,
 					logLevel: this._logService.getLevel(),
 					logsLocation: this._extensionHostLogsLocation,
-					autoStart: this._autoStart
+					autoStart: this._autoStart,
+					uiKind: UIKind.Desktop
 				};
 				return r;
 			});