diff --git a/src/vs/vscode.d.ts b/src/vs/vscode.d.ts
index 4b1673efdc6..6e349efdc7e 100644
--- a/src/vs/vscode.d.ts
+++ b/src/vs/vscode.d.ts
@@ -1860,6 +1860,12 @@ declare module 'vscode' {
 		 * Indicates that this message should be modal.
 		 */
 		modal?: boolean;
+
+		/**
+		 * Human-readable detail message that is rendered less prominent. _Note_ that detail
+		 * is only shown for {@link MessageOptions.modal modal} messages.
+		 */
+		detail?: string;
 	}
 
 	/**
diff --git a/src/vs/workbench/api/browser/mainThreadMessageService.ts b/src/vs/workbench/api/browser/mainThreadMessageService.ts
index f61b2cd5ec0..aaf480f8b67 100644
--- a/src/vs/workbench/api/browser/mainThreadMessageService.ts
+++ b/src/vs/workbench/api/browser/mainThreadMessageService.ts
@@ -33,7 +33,7 @@ export class MainThreadMessageService implements MainThreadMessageServiceShape {
 
 	$showMessage(severity: Severity, message: string, options: MainThreadMessageOptions, commands: { title: string; isCloseAffordance: boolean; handle: number; }[]): Promise<number | undefined> {
 		if (options.modal) {
-			return this._showModalMessage(severity, message, commands, options.useCustom);
+			return this._showModalMessage(severity, message, options.detail, commands, options.useCustom);
 		} else {
 			return this._showMessage(severity, message, commands, options.extension);
 		}
@@ -100,7 +100,7 @@ export class MainThreadMessageService implements MainThreadMessageServiceShape {
 		});
 	}
 
-	private async _showModalMessage(severity: Severity, message: string, commands: { title: string; isCloseAffordance: boolean; handle: number; }[], useCustom?: boolean): Promise<number | undefined> {
+	private async _showModalMessage(severity: Severity, message: string, detail: string | undefined, commands: { title: string; isCloseAffordance: boolean; handle: number; }[], useCustom?: boolean): Promise<number | undefined> {
 		let cancelId: number | undefined = undefined;
 
 		const buttons = commands.map((command, index) => {
@@ -121,7 +121,7 @@ export class MainThreadMessageService implements MainThreadMessageServiceShape {
 			cancelId = buttons.length - 1;
 		}
 
-		const { choice } = await this._dialogService.show(severity, message, buttons, { cancelId, custom: useCustom });
+		const { choice } = await this._dialogService.show(severity, message, buttons, { cancelId, custom: useCustom, detail });
 		return choice === commands.length ? undefined : commands[choice].handle;
 	}
 }
diff --git a/src/vs/workbench/api/common/extHost.protocol.ts b/src/vs/workbench/api/common/extHost.protocol.ts
index 74fe7b5b4c0..333888d4a87 100644
--- a/src/vs/workbench/api/common/extHost.protocol.ts
+++ b/src/vs/workbench/api/common/extHost.protocol.ts
@@ -423,6 +423,7 @@ export interface MainThreadLanguagesShape extends IDisposable {
 export interface MainThreadMessageOptions {
 	extension?: IExtensionDescription;
 	modal?: boolean;
+	detail?: string;
 	useCustom?: boolean;
 }
 
diff --git a/src/vs/workbench/api/common/extHostMessageService.ts b/src/vs/workbench/api/common/extHostMessageService.ts
index 847a27a2b5e..9f36d8dd3ac 100644
--- a/src/vs/workbench/api/common/extHostMessageService.ts
+++ b/src/vs/workbench/api/common/extHostMessageService.ts
@@ -37,8 +37,9 @@ export class ExtHostMessageService {
 		if (typeof optionsOrFirstItem === 'string' || isMessageItem(optionsOrFirstItem)) {
 			items = [optionsOrFirstItem, ...rest];
 		} else {
-			options.modal = optionsOrFirstItem && optionsOrFirstItem.modal;
-			options.useCustom = optionsOrFirstItem && optionsOrFirstItem.useCustom;
+			options.modal = optionsOrFirstItem?.modal;
+			options.useCustom = optionsOrFirstItem?.useCustom;
+			options.detail = optionsOrFirstItem?.detail;
 			items = rest;
 		}