diff --git a/packages/isolated-extension-api/compile.tsconfig.json b/packages/isolated-extension-api/compile.tsconfig.json
index b8b72b49c8822..797c60148d07b 100644
--- a/packages/isolated-extension-api/compile.tsconfig.json
+++ b/packages/isolated-extension-api/compile.tsconfig.json
@@ -2,7 +2,12 @@
   "extends": "../../configs/base.tsconfig",
   "compilerOptions": {
     "rootDir": "src",
-    "outDir": "lib"
+    "outDir": "lib",
+    "lib": [
+      "es6",
+      "dom",
+      "webworker"
+    ]
   },
   "include": [
     "src"
diff --git a/packages/isolated-extension-api/src/api/extension-api.ts b/packages/isolated-extension-api/src/api/extension-api.ts
new file mode 100644
index 0000000000000..60d5b88221670
--- /dev/null
+++ b/packages/isolated-extension-api/src/api/extension-api.ts
@@ -0,0 +1,58 @@
+/*
+ * Copyright (C) 2018 Red Hat, Inc.
+ * All rights reserved. This program and the accompanying materials
+ * are made available under the terms of the Eclipse Public License v1.0
+ * which accompanies this distribution, and is available at
+ * http://www.eclipse.org/legal/epl-v10.html
+ *
+ * Contributors:
+ *   Red Hat, Inc. - initial API and implementation
+ */
+import { createProxyIdentifier, ProxyIdentifier } from './rpc-protocol';
+import * as theia from 'theia';
+/**
+ * A command handler is an implementation of a command.
+ *
+ * A command can have multiple handlers
+ * but they should be active in different contexts,
+ * otherwise first active will be executed.
+ */
+export interface CommandHandler {
+    /**
+     * Execute this handler.
+     */
+    execute(...args: any[]): any;
+    /**
+     * Test whether this handler is enabled (active).
+     */
+    isEnabled?(...args: any[]): boolean;
+    /**
+     * Test whether menu items for this handler should be visible.
+     */
+    isVisible?(...args: any[]): boolean;
+}
+
+export interface CommandRegistryMain {
+    /**
+     * Register the given command and handler if present.
+     *
+     * Throw if a command is already registered for the given command identifier.
+     */
+    registerCommand(command: theia.Command): void;
+
+    unregisterCommand(id: string): void;
+    executeCommand<T>(id: string, args: any[]): PromiseLike<T>;
+    getCommands(): PromiseLike<string[]>;
+}
+
+export interface CommandRegistryExt {
+    executeContributedCommand<T>(id: string): PromiseLike<T>;
+}
+
+export const EXTENSION_RPC_CONTEXT = {
+    COMMAND_REGISTRY_MAIN: <ProxyIdentifier<CommandRegistryMain>>createProxyIdentifier<CommandRegistryMain>("CommandRegistryMain")
+};
+
+export const MAIN_RPC_CONTEXT = {
+    COMMAND_REGISTRY_EXT: createProxyIdentifier<CommandRegistryExt>("CommandRegistryExt")
+};
diff --git a/packages/isolated-extension-api/src/api/rpc-protocol.ts b/packages/isolated-extension-api/src/api/rpc-protocol.ts
index 94df23eb79d65..9d1157b05e174 100644
--- a/packages/isolated-extension-api/src/api/rpc-protocol.ts
+++ b/packages/isolated-extension-api/src/api/rpc-protocol.ts
@@ -23,6 +23,11 @@ export interface RPCProtocol {
      */
     getProxy<T>(proxyId: ProxyIdentifier<T>): T;
 
+    /**
+     * Register manually created instance.
+     */
+    set<T, R extends T>(identifier: ProxyIdentifier<T>, instance: R): R;
+
 }
 
 export class ProxyIdentifier<T> {
@@ -33,15 +38,12 @@ export class ProxyIdentifier<T> {
     }
 }
 
-export function createMainProxyIdentifier<T>(identifier: string): ProxyIdentifier<T> {
-    return new ProxyIdentifier(true, 'm' + identifier);
-}
-
-export function createExtensionProxyIdentifier<T>(identifier: string): ProxyIdentifier<T> {
-    return new ProxyIdentifier(false, 'e' + identifier);
+export function createProxyIdentifier<T>(identifier: string): ProxyIdentifier<T> {
+    return new ProxyIdentifier(false, identifier);
 }
 
 export class RPCProtocolImpl implements RPCProtocol {
+
     private isDisposed: boolean;
     private readonly locals: { [id: string]: any; };
     private readonly proxies: { [id: string]: any; };
@@ -66,10 +68,15 @@ export class RPCProtocolImpl implements RPCProtocol {
         return this.proxies[proxyId.id];
     }
 
+    set<T, R extends T>(identifier: ProxyIdentifier<T>, instance: R): R {
+        this.locals[identifier.id] = instance;
+        return instance;
+    }
+
     private createProxy<T>(proxyId: string): T {
         const handler = {
             get: (target: any, name: string) => {
-                if (!target[name] && name.charCodeAt(0) === 36 /* CharCode.DollarSign */) {
+                if (!target[name] /*&& name.charCodeAt(0) === 36 */ /* CharCode.DollarSign */) {
                     target[name] = (...myArgs: any[]) =>
                         this.remoteCall(proxyId, name, myArgs);
                 }
diff --git a/packages/isolated-extension-api/src/browser/command-registry-main.ts b/packages/isolated-extension-api/src/browser/command-registry-main.ts
new file mode 100644
index 0000000000000..9c65b57970e8c
--- /dev/null
+++ b/packages/isolated-extension-api/src/browser/command-registry-main.ts
@@ -0,0 +1,53 @@
+/*
+ * Copyright (C) 2015-2018 Red Hat, Inc.
+ * All rights reserved. This program and the accompanying materials
+ * are made available under the terms of the Eclipse Public License v1.0
+ * which accompanies this distribution, and is available at
+ * http://www.eclipse.org/legal/epl-v10.html
+ *
+ * Contributors:
+ *   Red Hat, Inc. - initial API and implementation
+ */
+import { CommandRegistryExt, MAIN_RPC_CONTEXT, CommandRegistryMain } from '../api/extension-api';
+import { injectable, inject } from "inversify";
+import { CommandRegistry } from '@theia/core/lib/common/command';
+import { ExtensionWorker } from './extension-worker';
+import * as theia from 'theia';
+import { Disposable } from '@theia/core/lib/common/disposable';
+
+@injectable()
+export class CommandRegistryMainImpl implements CommandRegistryMain {
+    private proxy: CommandRegistryExt;
+    private disposables = new Map<string, Disposable>();
+
+    constructor( @inject(CommandRegistry) private readonly delegate: CommandRegistry,
+        @inject(ExtensionWorker) worker: ExtensionWorker) {
+        this.proxy = worker.rpc.getProxy(MAIN_RPC_CONTEXT.COMMAND_REGISTRY_EXT);
+    }
+
+    registerCommand(command: theia.Command): void {
+        this.disposables.set(
+            command.id,
+            this.delegate.registerCommand(command, {
+                execute: (...args: any[]) => {
+                    this.proxy.executeContributedCommand(command.id);
+                },
+                isEnabled() { return true; },
+                isVisible() { return true; }
+            }));
+    }
+    unregisterCommand(id: string): void {
+        const dis = this.disposables.get(id);
+        if (dis) {
+            dis.dispose();
+            this.disposables.delete(id);
+        }
+    }
+    executeCommand<T>(id: string, args: any[]): PromiseLike<T> {
+        throw new Error("Method not implemented.");
+    }
+    getCommands(): PromiseLike<string[]> {
+        throw new Error("Method not implemented.");
+    }
+
+}
diff --git a/packages/isolated-extension-api/src/browser/extension-api-frontend-module.ts b/packages/isolated-extension-api/src/browser/extension-api-frontend-module.ts
index 3fc17a7919890..6b28eef5fe3a6 100644
--- a/packages/isolated-extension-api/src/browser/extension-api-frontend-module.ts
+++ b/packages/isolated-extension-api/src/browser/extension-api-frontend-module.ts
@@ -11,15 +11,19 @@
 import { ContainerModule } from "inversify";
 import { FrontendApplicationContribution, FrontendApplication } from "@theia/core/lib/browser";
 import { MaybePromise } from "@theia/core/lib/common";
+import { ExtensionWorker } from './extension-worker';
+import { CommandRegistryMainImpl } from './command-registry-main';
+import { EXTENSION_RPC_CONTEXT } from '../api/extension-api';
 
 export default new ContainerModule(bind => {
+    bind(ExtensionWorker).toSelf().inSingletonScope();
+    bind(CommandRegistryMainImpl).toSelf().inSingletonScope();
+    // bind(FrontendApplicationContribution).toService(ExtensionWorker);
     bind(FrontendApplicationContribution).toDynamicValue(ctx => ({
         onStart(app: FrontendApplication): MaybePromise<void> {
-
-            const worker: Worker = new (require('../worker/worker-main'));
-            worker.addEventListener('message', message => {
-                console.log('message is', message);
-            });
+            const worker = ctx.container.get(ExtensionWorker);
+            const commandRegistryMain = ctx.container.get(CommandRegistryMainImpl);
+            worker.rpc.set(EXTENSION_RPC_CONTEXT.COMMAND_REGISTRY_MAIN, commandRegistryMain);
         }
     }));
 });
diff --git a/packages/isolated-extension-api/src/browser/extension-worker.ts b/packages/isolated-extension-api/src/browser/extension-worker.ts
new file mode 100644
index 0000000000000..e165863677a69
--- /dev/null
+++ b/packages/isolated-extension-api/src/browser/extension-worker.ts
@@ -0,0 +1,33 @@
+/*
+ * Copyright (C) 2015-2018 Red Hat, Inc.
+ * All rights reserved. This program and the accompanying materials
+ * are made available under the terms of the Eclipse Public License v1.0
+ * which accompanies this distribution, and is available at
+ * http://www.eclipse.org/legal/epl-v10.html
+ *
+ * Contributors:
+ *   Red Hat, Inc. - initial API and implementation
+ */
+import { injectable } from "inversify";
+import { RPCProtocolImpl, RPCProtocol } from '../api/rpc-protocol';
+import { Emitter } from '@theia/core/lib/common/event';
+
+@injectable()
+export class ExtensionWorker {
+
+    private worker: Worker;
+    public readonly rpc: RPCProtocol;
+    constructor() {
+        const emmitter = new Emitter();
+        this.worker = new (require('../worker/worker-main'));
+        this.worker.onmessage = (message) => {
+            emmitter.fire(message.data);
+        };
+
+        this.rpc = new RPCProtocolImpl({
+            onMessage: emmitter.event,
+            send: (m: {}) => this.worker.postMessage(m)
+        });
+
+    }
+}
diff --git a/packages/isolated-extension-api/src/extension/comand-registry.ts b/packages/isolated-extension-api/src/extension/comand-registry.ts
new file mode 100644
index 0000000000000..024df391f48a0
--- /dev/null
+++ b/packages/isolated-extension-api/src/extension/comand-registry.ts
@@ -0,0 +1,52 @@
+/*
+ * Copyright (C) 2018 Red Hat, Inc.
+ * All rights reserved. This program and the accompanying materials
+ * are made available under the terms of the Eclipse Public License v1.0
+ * which accompanies this distribution, and is available at
+ * http://www.eclipse.org/legal/epl-v10.html
+ *
+ * Contributors:
+ *   Red Hat, Inc. - initial API and implementation
+ */
+import { CommandRegistryExt, EXTENSION_RPC_CONTEXT as Ext, CommandRegistryMain } from '../api/extension-api';
+import { Disposable } from '@theia/core/lib/common/disposable';
+import { RPCProtocol } from '../api/rpc-protocol';
+import * as theia from 'theia';
+
+export type Handler = <T>(...args: any[]) => T | PromiseLike<T>;
+
+export class CommandRegistryImpl implements CommandRegistryExt {
+
+    private proxy: CommandRegistryMain;
+    private commands = new Map<string, Handler>();
+
+    constructor(rpc: RPCProtocol) {
+        this.proxy = rpc.getProxy(Ext.COMMAND_REGISTRY_MAIN);
+    }
+    registerCommand(command: theia.Command, handler: Handler): Disposable {
+        if (this.commands.has(command.id)) {
+            throw new Error(`Command ${command.id} already exist`);
+        }
+        this.commands.set(command.id, handler);
+        this.proxy.registerCommand(command);
+
+        return Disposable.create(() => {
+            this.proxy.unregisterCommand(command.id);
+        });
+
+    }
+
+    dispose(): void {
+        throw new Error("Method not implemented.");
+    }
+
+    executeContributedCommand<T>(id: string): PromiseLike<T> {
+        const handler = this.commands.get(id);
+        if (handler) {
+            return Promise.resolve(handler());
+        } else {
+            return Promise.reject(new Error(`Command ${id} doesn't exist`));
+        }
+    }
+
+}
diff --git a/packages/isolated-extension-api/src/extension/extension-context.ts b/packages/isolated-extension-api/src/extension/extension-context.ts
new file mode 100644
index 0000000000000..e04044e02fc9e
--- /dev/null
+++ b/packages/isolated-extension-api/src/extension/extension-context.ts
@@ -0,0 +1,29 @@
+/*
+ * Copyright (C) 2018 Red Hat, Inc.
+ * All rights reserved. This program and the accompanying materials
+ * are made available under the terms of the Eclipse Public License v1.0
+ * which accompanies this distribution, and is available at
+ * http://www.eclipse.org/legal/epl-v10.html
+ *
+ * Contributors:
+ *   Red Hat, Inc. - initial API and implementation
+ */
+import { MAIN_RPC_CONTEXT } from '../api/extension-api';
+import { Disposable } from '@theia/core/lib/common/disposable';
+import { RPCProtocol } from '../api/rpc-protocol';
+import * as theia from 'theia';
+import { CommandRegistryImpl } from './comand-registry';
+
+export function createAPI(rpc: RPCProtocol): typeof theia {
+    const commandRegistryExt = rpc.set(MAIN_RPC_CONTEXT.COMMAND_REGISTRY_EXT, new CommandRegistryImpl(rpc));
+
+    const commands: typeof theia.commands = {
+        registerCommand(command: theia.Command, callback: <T>(...args: any[]) => T | Thenable<T>): Disposable {
+            return commandRegistryExt.registerCommand(command, callback);
+        }
+    };
+    return <typeof theia>{
+        commands
+    };
+
+}
diff --git a/packages/isolated-extension-api/src/theia.d.ts b/packages/isolated-extension-api/src/theia.d.ts
new file mode 100644
index 0000000000000..06725d37083dd
--- /dev/null
+++ b/packages/isolated-extension-api/src/theia.d.ts
@@ -0,0 +1,36 @@
+/*
+ * Copyright (C) 2018 Red Hat, Inc.
+ * All rights reserved. This program and the accompanying materials
+ * are made available under the terms of the Eclipse Public License v1.0
+ * which accompanies this distribution, and is available at
+ * http://www.eclipse.org/legal/epl-v10.html
+ *
+ * Contributors:
+ *   Red Hat, Inc. - initial API and implementation
+ */
+//import { Disposable } from '@theia/core/lib/common/disposable';
+
+declare module 'theia' {
+    /**
+     * A command is a unique identifier of a function
+     * which can be executed by a user via a keyboard shortcut,
+     * a menu action or directly.
+     */
+    export interface Command {
+        /**
+         * A unique identifier of this command.
+         */
+        id: string;
+        /**
+         * A label of this command.
+         */
+        label?: string;
+        /**
+         * An icon class of this command.
+         */
+        iconClass?: string;
+    }
+    export namespace commands {
+        export function registerCommand(command: Command, callback: (...args: any[]) => any): Disposable
+    }
+}
\ No newline at end of file
diff --git a/packages/isolated-extension-api/src/worker/worker-main.ts b/packages/isolated-extension-api/src/worker/worker-main.ts
index d846ab540c4cb..7c3bbcdcc0b65 100644
--- a/packages/isolated-extension-api/src/worker/worker-main.ts
+++ b/packages/isolated-extension-api/src/worker/worker-main.ts
@@ -9,17 +9,11 @@
  *   Red Hat, Inc. - initial API and implementation
  */
 
-import { RPCProtocolImpl, createExtensionProxyIdentifier } from '../api/rpc-protocol';
+import { RPCProtocolImpl } from '../api/rpc-protocol';
 import { Emitter } from '@theia/core/lib/common/event';
-import { Disposable } from '@theia/core/lib/common/disposable';
-export interface MainThreadCommandsShape extends Disposable {
-    $registerCommand(id: string): void;
-    $unregisterCommand(id: string): void;
-    $executeCommand<T>(id: string, args: any[]): Thenable<T>;
-    $getCommands(): Thenable<string[]>;
-}
+import { createAPI } from '../extension/extension-context';
 
-const ctx: Worker = self as any;
+const ctx: DedicatedWorkerGlobalScope = self as any;
 
 const emmitter = new Emitter();
 const rpc = new RPCProtocolImpl({
@@ -32,8 +26,7 @@ addEventListener('message', (message: any) => {
     emmitter.fire(message.data);
 });
 
-const ExtHostCommands = createExtensionProxyIdentifier<MainThreadCommandsShape>("MainThreadCommands");
-
-const proxy = rpc.getProxy(ExtHostCommands);
-
-proxy.$registerCommand('foo');
+const api = createAPI(rpc);
+api.commands.registerCommand({ id: 'fooBar', label: 'Command From Extension' }, () => {
+    console.log("Hello from WebWorker Command");
+});