diff --git a/src/vs/vscode.proposed.d.ts b/src/vs/vscode.proposed.d.ts
index 2edbc6a4220..3a59c0a4906 100644
--- a/src/vs/vscode.proposed.d.ts
+++ b/src/vs/vscode.proposed.d.ts
@@ -1051,6 +1051,15 @@ declare module 'vscode' {
 
 	export interface WebviewEditor extends WebviewPanel {
 		state: WebviewEditorState;
+
+		/**
+		 * Fired when the webview editor is saved.
+		 *
+		 * Both `Unchanged` and `Dirty` editors can be saved.
+		 *
+		 * Extensions should call `waitUntil` to signal when the save operation complete
+		 */
+		readonly onWillSave: Event<{ waitUntil: (thenable: Thenable<boolean>) => void }>;
 	}
 
 	export interface WebviewEditorProvider {
diff --git a/src/vs/workbench/api/browser/mainThreadWebview.ts b/src/vs/workbench/api/browser/mainThreadWebview.ts
index 17f3257380f..4fa2a398e0e 100644
--- a/src/vs/workbench/api/browser/mainThreadWebview.ts
+++ b/src/vs/workbench/api/browser/mainThreadWebview.ts
@@ -16,13 +16,13 @@ import { IProductService } from 'vs/platform/product/common/product';
 import { ITelemetryService } from 'vs/platform/telemetry/common/telemetry';
 import { ExtHostContext, ExtHostWebviewsShape, IExtHostContext, MainContext, MainThreadWebviewsShape, WebviewPanelHandle, WebviewPanelShowOptions, WebviewPanelViewStateData } from 'vs/workbench/api/common/extHost.protocol';
 import { editorGroupToViewColumn, EditorViewColumn, viewColumnToEditorGroup } from 'vs/workbench/api/common/shared/editor';
+import { CustomFileEditorInput } from 'vs/workbench/contrib/customEditor/browser/customEditorInput';
 import { WebviewInput } from 'vs/workbench/contrib/webview/browser/webviewEditorInput';
 import { ICreateWebViewShowOptions, IWebviewEditorService, WebviewInputOptions } from 'vs/workbench/contrib/webview/browser/webviewEditorService';
 import { IEditorGroupsService } from 'vs/workbench/services/editor/common/editorGroupsService';
 import { IEditorService } from 'vs/workbench/services/editor/common/editorService';
 import { IExtensionService } from 'vs/workbench/services/extensions/common/extensions';
 import { extHostNamedCustomer } from '../common/extHostCustomers';
-import { CustomFileEditorInput } from 'vs/workbench/contrib/customEditor/browser/customEditorInput';
 
 /**
  * Bi-directional map between webview handles and inputs.
@@ -253,6 +253,12 @@ export class MainThreadWebviews extends Disposable implements MainThreadWebviews
 				this._webviewEditorInputs.add(handle, webview);
 				this.hookupWebviewEventDelegate(handle, webview);
 
+				if (webview instanceof CustomFileEditorInput) {
+					webview.onWillSave(e => {
+						e.waitUntil(this._proxy.$save(handle));
+					});
+				}
+
 				try {
 					await this._proxy.$resolveWebviewEditor(
 						webview.getResource(),
diff --git a/src/vs/workbench/api/common/extHost.protocol.ts b/src/vs/workbench/api/common/extHost.protocol.ts
index b7bddc60c4d..31f17645dff 100644
--- a/src/vs/workbench/api/common/extHost.protocol.ts
+++ b/src/vs/workbench/api/common/extHost.protocol.ts
@@ -573,6 +573,7 @@ export interface ExtHostWebviewsShape {
 	$onDidDisposeWebviewPanel(handle: WebviewPanelHandle): Promise<void>;
 	$deserializeWebviewPanel(newWebviewHandle: WebviewPanelHandle, viewType: string, title: string, state: any, position: EditorViewColumn, options: modes.IWebviewOptions & modes.IWebviewPanelOptions): Promise<void>;
 	$resolveWebviewEditor(resource: UriComponents, newWebviewHandle: WebviewPanelHandle, viewType: string, title: string, state: any, position: EditorViewColumn, options: modes.IWebviewOptions & modes.IWebviewPanelOptions): Promise<void>;
+	$save(handle: WebviewPanelHandle): Promise<boolean>;
 }
 
 export interface MainThreadUrlsShape extends IDisposable {
diff --git a/src/vs/workbench/api/common/extHostWebview.ts b/src/vs/workbench/api/common/extHostWebview.ts
index 2ba9d4eb252..f3717e325c8 100644
--- a/src/vs/workbench/api/common/extHostWebview.ts
+++ b/src/vs/workbench/api/common/extHostWebview.ts
@@ -224,6 +224,18 @@ export class ExtHostWebviewEditor implements vscode.WebviewEditor {
 		this._proxy.$setState(this._handle, typeConverters.WebviewEditorState.from(newState));
 	}
 
+	private readonly _onWillSave = new Emitter<{ waitUntil: (thenable: Thenable<boolean>) => void }>();
+	public readonly onWillSave = this._onWillSave.event;
+
+	async _save(): Promise<boolean> {
+		const waitingOn: Thenable<boolean>[] = [];
+		this._onWillSave.fire({
+			waitUntil: (thenable: Thenable<boolean>): void => { waitingOn.push(thenable); },
+		});
+		const result = await Promise.all(waitingOn);
+		return result.every(x => x);
+	}
+
 	public postMessage(message: any): Promise<boolean> {
 		this.assertNotDisposed();
 		return this._proxy.$postMessage(this._handle, message);
@@ -422,6 +434,13 @@ export class ExtHostWebviews implements ExtHostWebviewsShape {
 		return Promise.resolve(provider.resolveWebviewEditor(URI.revive(resource), revivedPanel));
 	}
 
+	async $save(handle: WebviewPanelHandle): Promise<boolean> {
+		const panel = this.getWebviewPanel(handle);
+		if (panel) {
+			return panel._save();
+		}
+		return false;
+	}
 }
 
 function convertWebviewOptions(
diff --git a/src/vs/workbench/contrib/customEditor/browser/customEditorInput.ts b/src/vs/workbench/contrib/customEditor/browser/customEditorInput.ts
index 19dc5014d9c..776eb29464f 100644
--- a/src/vs/workbench/contrib/customEditor/browser/customEditorInput.ts
+++ b/src/vs/workbench/contrib/customEditor/browser/customEditorInput.ts
@@ -4,6 +4,7 @@
  *--------------------------------------------------------------------------------------------*/
 
 import { memoize } from 'vs/base/common/decorators';
+import { Emitter } from 'vs/base/common/event';
 import { UnownedDisposable } from 'vs/base/common/lifecycle';
 import { basename } from 'vs/base/common/path';
 import { URI } from 'vs/base/common/uri';
@@ -115,7 +116,17 @@ export class CustomFileEditorInput extends WebviewInput {
 	}
 
 	public async save(): Promise<boolean> {
-		// TODO
-		return true;
+		if (!this.isDirty) {
+			return true;
+		}
+		const waitingOn: Promise<boolean>[] = [];
+		this._onWillSave.fire({
+			waitUntil: (thenable: Promise<boolean>): void => { waitingOn.push(thenable); },
+		});
+		const result = await Promise.all(waitingOn);
+		return result.every(x => x);
 	}
+
+	private readonly _onWillSave = this._register(new Emitter<{ waitUntil: (thenable: Thenable<boolean>) => void }>());
+	public readonly onWillSave = this._onWillSave.event;
 }