diff --git a/.gitignore b/.gitignore
index 4fa1889..70fdc89 100644
--- a/.gitignore
+++ b/.gitignore
@@ -2,3 +2,4 @@ out/
 node_modules/
 vendor/
 composer.lock
+typings/
diff --git a/package.json b/package.json
index e4e8719..76b249c 100644
--- a/package.json
+++ b/package.json
@@ -50,6 +50,7 @@
     "vscode": "^0.11.17"
   },
   "dependencies": {
+    "semver": "^5.3.0",
     "vscode-languageclient": "^2.4.2-next.13"
   }
 }
diff --git a/src/extension.ts b/src/extension.ts
index 4ae49b3..1e095b6 100644
--- a/src/extension.ts
+++ b/src/extension.ts
@@ -1,42 +1,66 @@
 'use strict';
 
 import * as path from 'path';
-import { spawn } from 'child_process';
-import { ExtensionContext } from 'vscode';
-import { LanguageClient, LanguageClientOptions } from 'vscode-languageclient';
+import { spawn, execFile, ChildProcess } from 'child_process';
+import * as vscode from 'vscode';
+import { LanguageClient, LanguageClientOptions, StreamInfo } from 'vscode-languageclient';
+import * as semver from 'semver';
 
-export function activate(context: ExtensionContext) {
+export function activate(context: vscode.ExtensionContext) {
 
-    // The server is implemented in PHP
-    const serverPath = context.asAbsolutePath(path.join('vendor', 'felixfbecker', 'language-server', 'bin', 'php-language-server.php'));
+    // Check if PHP is available and version is ^7.0.0
+    execFile('php', ['--version'], (err: NodeJS.ErrnoException, stdout: Buffer, stderr: Buffer) => {
 
-    const serverOptions = () => {
-        const childProcess = spawn('php', [serverPath]);
-        childProcess.stderr.on('data', (chunk: Buffer) => {
-            console.error(chunk + '');
-        });
-        childProcess.stdout.on('data', (chunk: Buffer) => {
-            console.log(chunk + '');
-        });
-        return Promise.resolve(childProcess);
-    };
+        if (err) {
+            if (err.code === 'ENOENT') {
+                vscode.window.showErrorMessage('PHP executable not found. You need PHP 7 installed and in your PATH');
+            } else {
+                vscode.window.showErrorMessage('Error spawning PHP: ' + err.message);
+                console.error(err);
+            }
+            return;
+        }
 
-    // Options to control the language client
-    let clientOptions: LanguageClientOptions = {
-        // Register the server for php documents
-        documentSelector: ['php']
-        // synchronize: {
-        //     // Synchronize the setting section 'php' to the server
-        //     configurationSection: 'php',
-        //     // Notify the server about file changes to composer.json files contain in the workspace
-        //     fileEvents: workspace.createFileSystemWatcher('**/composer.json')
-        // }
-    };
+        let version = stdout.toString().match(/^PHP ([^\s]+)/)[1];
+        // Convert PHP prerelease format like 7.0.0rc1 to 7.0.0-rc1
+        if (!/^\d+.\d+.\d+$/.test(version)) {
+            version = version.replace(/(\d+.\d+.\d+)/, '$1-');
+        }
+        if (!semver.satisfies(version, '^7.0.0')) {
+            vscode.window.showErrorMessage('The language server needs at least PHP 7 installed and in your PATH. Version found: ' + version);
+            return;
+        }
 
-    // Create the language client and start the client.
-    const disposable = new LanguageClient('PHP Language Client', serverOptions, clientOptions).start();
+        const serverOptions = (): Promise<ChildProcess | StreamInfo> => {
+            // The server is implemented in PHP
+            const serverPath = context.asAbsolutePath(path.join('vendor', 'felixfbecker', 'language-server', 'bin', 'php-language-server.php'));
+            const childProcess = spawn('php', [serverPath]);
+            childProcess.stderr.on('data', (chunk: Buffer) => {
+                console.error(chunk + '');
+            });
+            childProcess.stdout.on('data', (chunk: Buffer) => {
+                console.log(chunk + '');
+            });
+            return Promise.resolve(childProcess);
+        };
 
-    // Push the disposable to the context's subscriptions so that the
-    // client can be deactivated on extension deactivation
-    context.subscriptions.push(disposable);
+        // Options to control the language client
+        let clientOptions: LanguageClientOptions = {
+            // Register the server for php documents
+            documentSelector: ['php']
+            // synchronize: {
+            //     // Synchronize the setting section 'php' to the server
+            //     configurationSection: 'php',
+            //     // Notify the server about file changes to composer.json files contain in the workspace
+            //     fileEvents: workspace.createFileSystemWatcher('**/composer.json')
+            // }
+        };
+
+        // Create the language client and start the client.
+        const disposable = new LanguageClient('PHP Language Client', serverOptions, clientOptions).start();
+
+        // Push the disposable to the context's subscriptions so that the
+        // client can be deactivated on extension deactivation
+        context.subscriptions.push(disposable);
+    });
 }
diff --git a/tsconfig.json b/tsconfig.json
index 7076a94..bf51f69 100644
--- a/tsconfig.json
+++ b/tsconfig.json
@@ -5,6 +5,7 @@
 		"moduleResolution": "node",
 		"outDir": "out",
 		"noLib": true,
+    "noImplicitAny": true,
 		"sourceMap": true,
     "rootDir": "src"
 	},
diff --git a/typings.json b/typings.json
new file mode 100644
index 0000000..ae4f099
--- /dev/null
+++ b/typings.json
@@ -0,0 +1,5 @@
+{
+  "dependencies": {
+    "semver": "registry:npm/semver#5.0.0+20160723033700"
+  }
+}