n8n-io/n8n · warning · UnsupportedOperationError

Operation not supported: dialog

Error message

Operation not supported: dialog

What it means

Thrown as UnsupportedOperationError('dialog', 'agent-browser') by the agent-browser adapter's dialog() stub. The agent-browser CLI has no JavaScript dialog (alert/confirm/prompt) handling, so the adapter explicitly rejects the operation. UnsupportedOperationError extends McpBrowserError. The Playwright adapter supports dialog handling; agent-browser does not.

Source

Thrown at packages/@n8n/mcp-browser/src/adapters/agent-browser.ts:426

				'scroll',
				options?.direction ?? 'down',
				String(options?.amount ?? 300),
			]);
		}
	}

	async upload(
		_pageId: string,
		_target: ElementTarget | undefined,
		_files: string[],
	): Promise<void> {
		await Promise.resolve();
		throw new UnsupportedOperationError('upload', this.name);
	}

	async dialog(_pageId: string, _action: 'accept' | 'dismiss', _text?: string): Promise<string> {
		await Promise.resolve();
		throw new UnsupportedOperationError('dialog', this.name);
	}

	// =========================================================================
	// Inspection
	// =========================================================================

	async snapshot(
		pageId: string,
		_target?: ElementTarget,
		interactive = true,
	): Promise<SnapshotResult> {
		await this.switchToTab(pageId);
		const args = interactive ? ['snapshot', '-i'] : ['snapshot'];
		const response = await this.run(args);
		const tree =
			typeof response.data === 'string' ? response.data : JSON.stringify(response.data ?? '');
		const refCount = (tree.match(/@e\d+/g) ?? []).length;
		return { tree: tree || '(empty page)', refCount };

View on GitHub (pinned to 5ac6606e81)

Solutions

1. Switch to the Playwright adapter for sessions that may encounter JS dialogs.
2. Gate dialog handling behind adapter.name === 'playwright' before calling.
3. For agent-browser, dismiss dialogs manually via evaluate() that overrides window.alert/confirm, or accept them in the browser UI.

Example fix

// before
await adapter.dialog(pageId, 'accept');

// after — dismiss via eval on agent-browser
if (adapter.name === 'agent-browser') {
  await adapter.evaluate(pageId, 'window.confirm = () => true;');
} else {
  await adapter.dialog(pageId, 'accept');
}

function adapterSupportsDialog(name: string): boolean {
  return name === 'playwright';
}

function supportsDialog(adapter: Adapter): boolean {
  return adapter.name !== 'agent-browser';
}

When it happens

Trigger: Calling adapter.dialog(pageId, 'accept' | 'dismiss', text?) on an AgentBrowserAdapter instance. The method awaits a resolved promise then throws synchronously.

Common situations: A page showed a JS alert/confirm and the tool layer tried to dismiss it generically; migrating from Playwright adapter to agent-browser; an LLM emitted a dialog tool call against an agent-browser session.

Related errors

• Operation not supported: drag
• Operation not supported: upload
• Operation not supported: pdf
• agent-browser failed
• Page not found: ${pageId}

AI-assisted analysis of n8n-io/n8n@5ac6606e81 (2026-08-12). Data as JSON: /api/errors/5b4cbdd693b4d888. Report an issue: GitHub.