n8n-io/n8n · error · UserError

MCP server " ": only http(s) URLs are allowed, got

Error message

MCP server "${server.name}": only http(s) URLs are allowed, got "${parsed.protocol}"

What it means

Config validation in McpClientManager.validateConfigs: the MCP server's URL parsed successfully but its scheme is not http/https (e.g. file:, ws:, or a bare host interpreted oddly). Only http(s) remotes are supported, and the message names the server and the offending protocol.

Solutions

1. Change the MCP server URL to start with http:// or https://
2. For local stdio servers, use the stdio transport config instead of a URL
3. Check for a missing scheme or copy-paste artifacts in the configured URL

When it happens

Trigger: Thrown at packages/@n8n/instance-ai/src/mcp/mcp-client-manager.ts:236 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of n8n-io/n8n@5ac6606e81 (2026-08-12). Data as JSON: /api/errors/f036c50096c7abc6. Report an issue: GitHub.

Appendix: source

Thrown at packages/@n8n/instance-ai/src/mcp/mcp-client-manager.ts:236

			return await promise;
		} finally {
			inFlight.delete(key);
		}
	}

	private async validateConfigs(configs: McpServerConfig[]): Promise<void> {
		for (const server of configs) {
			if (!server.url) continue;

			let parsed: URL;
			try {
				parsed = new URL(server.url);
			} catch {
				throw new UserError(`MCP server "${server.name}": invalid URL "${server.url}"`);
			}

			if (parsed.protocol !== 'http:' && parsed.protocol !== 'https:') {
				throw new UserError(
					`MCP server "${server.name}": only http(s) URLs are allowed, got "${parsed.protocol}"`,
				);
			}

			if (this.ssrfValidator) {
				const result = await this.ssrfValidator.validateUrl(server.url);
				if (!result.ok) {
					throw new UserError(
						`MCP server "${server.name}": URL blocked by SSRF policy - ${result.error.message}`,
					);
				}
			}
		}
	}

	private async connectAndListTools(
		configs: McpServerConfig[],
		clientKey: string,

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