diff --git a/extensions/git/src/commit.ts b/extensions/git/src/commit.ts
new file mode 100644
index 00000000000..6d471729774
--- /dev/null
+++ b/extensions/git/src/commit.ts
@@ -0,0 +1,50 @@
+/*---------------------------------------------------------------------------------------------
+ *  Copyright (c) Microsoft Corporation. All rights reserved.
+ *  Licensed under the MIT License. See License.txt in the project root for license information.
+ *--------------------------------------------------------------------------------------------*/
+
+'use strict';
+
+import { workspace, languages, Disposable, Uri, TextDocumentChangeEvent, DiagnosticCollection, Diagnostic, DiagnosticSeverity } from 'vscode';
+import { Model } from './model';
+import { filterEvent } from './util';
+import * as nls from 'vscode-nls';
+
+const localize = nls.loadMessageBundle();
+
+function isSCMInput(uri: Uri) {
+	return uri.toString() === 'scm:input';
+}
+
+// TODO@Joao: prevent these diagnostics from showing in global error/warnings
+// TODO@Joao: hover dissapears if editor is scrolled
+export class CommitHandler {
+
+	private diagnosticCollection: DiagnosticCollection;
+	private disposables: Disposable[] = [];
+
+	constructor(private model: Model) {
+		const onDidChange = filterEvent(workspace.onDidChangeTextDocument, e => e.document && isSCMInput(e.document.uri));
+		onDidChange(this.onSCMInputChange, this, this.disposables);
+
+		this.diagnosticCollection = languages.createDiagnosticCollection(localize('git commit message', "Git Commit Message"));
+		this.disposables.push(this.diagnosticCollection);
+	}
+
+	private onSCMInputChange(e: TextDocumentChangeEvent): void {
+		const uri = e.document.uri;
+		const firstLineRange = e.document.lineAt(0).range;
+		const firstLineLength = firstLineRange.end.character - firstLineRange.start.character;
+
+		if (firstLineLength > 80) {
+			const warning = new Diagnostic(firstLineRange, localize('too long', "You should keep the first line under 50 characters.\nYou can use more lines for extra information."), DiagnosticSeverity.Warning);
+			this.diagnosticCollection.set(uri, [warning]);
+		} else {
+			this.diagnosticCollection.clear();
+		}
+	}
+
+	dispose(): void {
+		this.disposables.forEach(d => d.dispose());
+	}
+}
diff --git a/extensions/git/src/main.ts b/extensions/git/src/main.ts
index 1df0364a6ad..a724582c0ed 100644
--- a/extensions/git/src/main.ts
+++ b/extensions/git/src/main.ts
@@ -15,6 +15,7 @@ import { filterEvent, anyEvent } from './util';
 import { GitContentProvider } from './contentProvider';
 import { AutoFetcher } from './autofetch';
 import { MergeDecorator } from './merge';
+import { CommitHandler } from './commit';
 import * as nls from 'vscode-nls';
 
 const localize = nls.config()();
@@ -48,6 +49,7 @@ async function init(disposables: Disposable[]): Promise<void> {
 	const syncStatusBar = new SyncStatusBar(model);
 	const autoFetcher = new AutoFetcher(model);
 	const mergeDecorator = new MergeDecorator(model);
+	const commitHandler = new CommitHandler(model);
 
 	disposables.push(
 		commandCenter,
@@ -58,7 +60,8 @@ async function init(disposables: Disposable[]): Promise<void> {
 		checkoutStatusBar,
 		syncStatusBar,
 		autoFetcher,
-		mergeDecorator
+		mergeDecorator,
+		commitHandler
 	);
 }
 
diff --git a/src/vs/editor/contrib/hover/browser/hover.ts b/src/vs/editor/contrib/hover/browser/hover.ts
index b2be03752c8..dc3e994478c 100644
--- a/src/vs/editor/contrib/hover/browser/hover.ts
+++ b/src/vs/editor/contrib/hover/browser/hover.ts
@@ -24,7 +24,7 @@ import { IDisposable, dispose } from 'vs/base/common/lifecycle';
 import EditorContextKeys = editorCommon.EditorContextKeys;
 
 @editorContribution
-class ModesHoverController implements editorCommon.IEditorContribution {
+export class ModesHoverController implements editorCommon.IEditorContribution {
 
 	private static ID = 'editor.contrib.hover';
 
diff --git a/src/vs/workbench/parts/scm/electron-browser/scmEditor.ts b/src/vs/workbench/parts/scm/electron-browser/scmEditor.ts
index 5cfa7c06e42..dda97403401 100644
--- a/src/vs/workbench/parts/scm/electron-browser/scmEditor.ts
+++ b/src/vs/workbench/parts/scm/electron-browser/scmEditor.ts
@@ -20,9 +20,9 @@ import { ContextMenuController } from 'vs/editor/contrib/contextmenu/browser/con
 import { SuggestController } from 'vs/editor/contrib/suggest/browser/suggestController';
 import { SnippetController } from 'vs/editor/contrib/snippet/common/snippetController';
 import { TabCompletionController } from 'vs/editor/contrib/suggest/browser/tabCompletion';
+import { ModesHoverController } from 'vs/editor/contrib/hover/browser/hover';
 import { IModelService } from 'vs/editor/common/services/modelService';
 import { IThemeService } from 'vs/workbench/services/themes/common/themeService';
-import { append, $ } from 'vs/base/browser/dom';
 import URI from 'vs/base/common/uri';
 import { IDisposable, dispose } from 'vs/base/common/lifecycle';
 import Event, { Emitter } from 'vs/base/common/event';
@@ -48,6 +48,7 @@ class SCMCodeEditorWidget extends CodeEditorWidget {
 			SuggestController,
 			SnippetController,
 			TabCompletionController,
+			ModesHoverController
 		];
 	}