n8n-io/n8n · warning · AlreadyConnectedError

Already connected to a browser

Error message

Already connected to a browser

What it means

AlreadyConnectedError is thrown by BrowserConnection.connect when this.state is already set — a prior connect() succeeded and the connection is live. The connection enforces single-active-session semantics; calling connect twice without an intervening disconnect is a programming error.

Source

Thrown at packages/@n8n/mcp-browser/src/connection.ts:95

				});
			}
		}

		this.config = {
			defaultBrowser: parsed.defaultBrowser,
			browsers,
			adapter: parsed.adapter,
			mode: parsed.mode,
		};
	}

	// -------------------------------------------------------------------------
	// Public API
	// -------------------------------------------------------------------------

	async connect(overrideBrowser?: BrowserName): Promise<ConnectResult> {
		if (this.state) {
			throw new AlreadyConnectedError();
		}

		const browser = overrideBrowser ?? this.config.defaultBrowser;
		if (this.config.mode !== 'remote') {
			this.requireBrowserAvailable(browser);
		}

		const connectConfig: ConnectConfig = {
			browser,
		};

		// Reuse a pending adapter (relay kept alive from a prior timeout) if available.
		const adapter = this.pendingAdapter ?? (await this.createAdapter());
		this.pendingAdapter = null;

		// Listen for unexpected disconnections so we can invalidate state immediately
		adapter.onDisconnect = (reason) => {
			if (!this.state) return; // already disconnected

View on GitHub (pinned to 5ac6606e81)

Solutions

1. Check connection.isConnected before calling connect, or call disconnect first.
2. Make connect idempotent in your wrapper: if (connection.isConnected) return;
3. In retry loops, ensure disconnect() runs before any reconnect attempt.

Example fix

// before — double connect
await connection.connect();
await connection.connect(); // throws AlreadyConnectedError

// after — guard with isConnected
if (!connection.isConnected) { await connection.connect(); }

if (connection.isConnected) { /* already connected, skip */ return; }
await connection.connect();

function isConnected(c: BrowserConnection): boolean {
  return c.isConnected;
}

try {
  await connection.connect();
} catch (e) {
  if (e instanceof AlreadyConnectedError) { /* no-op, already live */ }
  else throw e;
}

When it happens

Trigger: Invoking browser_connect when a connection already exists (isConnected === true). Common in agent loops that reconnect defensively without first checking state, or in retry logic that re-enters connect after a partial success.

Common situations: Agent retries connect after a slow-but-successful first attempt. Two concurrent tool calls both triggering a lazy connect. User-script calls connect in a loop without disconnect.

Related errors

• Not connected to a browser
• Cannot decrease maxIterations when resuming a run. Expected
• Checkpoint for runId ${this.runId} has pending tool calls —
• Model ID is required
• Invalid model ID "${rawId}": expected "provider/model-name"

AI-assisted analysis of n8n-io/n8n@5ac6606e81 (2026-08-12). Data as JSON: /api/errors/2cb93a2aa6abf883. Report an issue: GitHub.