diff --git a/extensions/vscode-api-tests/src/commands.test.ts b/extensions/vscode-api-tests/src/commands.test.ts
index 5ffd6fd2ac7..495de2d1d96 100644
--- a/extensions/vscode-api-tests/src/commands.test.ts
+++ b/extensions/vscode-api-tests/src/commands.test.ts
@@ -40,23 +40,6 @@ suite('commands namespace tests', () => {
 		}, done);
 	});
 
-	test('api-command: workbench.html.preview', function () {
-
-		let registration = workspace.registerTextDocumentContentProvider('speciale', {
-			provideTextDocumentContent(uri) {
-				return `content of URI <b>${uri.toString()}</b>`;
-			}
-		});
-
-		let virtualDocumentUri = Uri.parse('speciale://authority/path');
-
-		return commands.executeCommand('vscode.previewHtml', virtualDocumentUri).then(success => {
-			assert.ok(success);
-			registration.dispose();
-		});
-
-	});
-
 	test('editorCommand with extra args', function () {
 
 		let args: IArguments;
@@ -77,4 +60,46 @@ suite('commands namespace tests', () => {
 		});
 
 	});
+
+	test('api-command: vscode.previewHtm', function () {
+
+		let registration = workspace.registerTextDocumentContentProvider('speciale', {
+			provideTextDocumentContent(uri) {
+				return `content of URI <b>${uri.toString()}</b>`;
+			}
+		});
+
+		let virtualDocumentUri = Uri.parse('speciale://authority/path');
+
+		return commands.executeCommand('vscode.previewHtml', virtualDocumentUri).then(success => {
+			assert.ok(success);
+			registration.dispose();
+		});
+
+	});
+
+	test('api-command: vscode.diff', function () {
+
+		let registration = workspace.registerTextDocumentContentProvider('sc', {
+			provideTextDocumentContent(uri) {
+				return `content of URI <b>${uri.toString()}</b>#${Math.random()}`;
+			}
+		});
+
+
+		let a = commands.executeCommand('vscode.diff', Uri.parse('sc:a'), Uri.parse('sc:b'), 'DIFF').then(value => {
+			assert.ok(value === void 0);
+			registration.dispose();
+		});
+
+		let b = commands.executeCommand('vscode.diff', Uri.parse('sc:a'), Uri.parse('sc:b')).then(value => {
+			assert.ok(value === void 0);
+			registration.dispose();
+		});
+
+		let c = commands.executeCommand('vscode.diff').then(() => assert.ok(false), () => assert.ok(true));
+		let d = commands.executeCommand('vscode.diff', 1, 2, 3).then(() => assert.ok(false), () => assert.ok(true));
+
+		return Promise.all([a, b, c]);
+	});
 });
diff --git a/src/vs/workbench/api/node/extHostApiCommands.ts b/src/vs/workbench/api/node/extHostApiCommands.ts
index 92c8a164e52..666c57b577e 100644
--- a/src/vs/workbench/api/node/extHostApiCommands.ts
+++ b/src/vs/workbench/api/node/extHostApiCommands.ts
@@ -197,6 +197,17 @@ class ExtHostApiCommands {
 				{ name: 'configuration', description: '(optional) Name of the debug configuration from \'launch.json\' to use. Or a configuration json object to use.' }
 			]
 		});
+
+		this._register('vscode.diff', (left: URI, right: URI, label: string) => {
+			return this._commands.executeCommand('_workbench.diff', [left, right, label]);
+		}, {
+			description: 'Opens the provided resources in the diff editor to compare their contents.',
+			args: [
+				{ name: 'left', description: 'Left-hand side resource of the diff editor', constraint: URI },
+				{ name: 'right', description: 'Right-hand side resource of the diff editor', constraint: URI },
+				{ name: 'title', description: '(optional) Human readable title for the diff editor', constraint: v => v === void 0 || typeof v === 'string' }
+			]
+		});
 	}
 
 	// --- command impl
diff --git a/src/vs/workbench/electron-browser/actions.ts b/src/vs/workbench/electron-browser/actions.ts
index 217820b5640..635937fcf9f 100644
--- a/src/vs/workbench/electron-browser/actions.ts
+++ b/src/vs/workbench/electron-browser/actions.ts
@@ -5,12 +5,15 @@
 
 'use strict';
 
+import URI from 'vs/base/common/uri';
 import {TPromise} from 'vs/base/common/winjs.base';
 import timer = require('vs/base/common/timer');
 import paths = require('vs/base/common/paths');
 import {Action} from 'vs/base/common/actions';
 import {IWindowService} from 'vs/workbench/services/window/electron-browser/windowService';
 import {IWorkbenchEditorService} from 'vs/workbench/services/editor/common/editorService';
+import {EditorInput} from 'vs/workbench/common/editor';
+import {DiffEditorInput} from 'vs/workbench/common/editor/diffEditorInput';
 import nls = require('vs/nls');
 import {IMessageService, Severity} from 'vs/platform/message/common/message';
 import {IWindowConfiguration} from 'vs/workbench/electron-browser/window';
@@ -459,4 +462,29 @@ KeybindingsRegistry.registerCommandDesc({
 	},
 	when: undefined,
 	primary: undefined
+});
+
+KeybindingsRegistry.registerCommandDesc({
+	id: '_workbench.diff',
+	weight: KeybindingsRegistry.WEIGHT.workbenchContrib(0),
+	handler(accessor: ServicesAccessor, args: [URI, URI, string]) {
+
+		const editorService = accessor.get(IWorkbenchEditorService);
+		let [left, right, label] = args;
+
+		if (!label) {
+			label = nls.localize('diffLeftRightLabel', "{0} ⟷ {1}", left.toString(true), right.toString(true));
+		}
+
+		return TPromise.join([editorService.inputToType({ resource: left }), editorService.inputToType({ resource: right })]).then(inputs => {
+			const [left, right] = inputs;
+
+			const diff = new DiffEditorInput(label, undefined, <EditorInput>left, <EditorInput>right);
+			return editorService.openEditor(diff);
+		}).then(() => {
+			return void 0;
+		});
+	},
+	when: undefined,
+	primary: undefined
 });
\ No newline at end of file