alibaba/open-code-review · error

MCP server URL %q must include a host

Error message

MCP server URL %q must include a host

What it means

After the URL parses and passes the http/https scheme check, the setter requires a non-empty Host. A URL like 'http://' or a scheme-only/relative form has no host to connect to, so a remote MCP server configured with it would be unreachable; the setter rejects it with the original value quoted.

Source

Thrown at cmd/opencodereview/config_cmd.go:897

			idx := strings.Index(e, "=")
			if idx <= 0 {
				return fmt.Errorf("invalid env entry %q: must be in KEY=VALUE format", e)
			}
		}
		entry.Env = env
	case "url":
		if value == "" {
			return fmt.Errorf("MCP server URL cannot be empty")
		}
		parsed, err := url.Parse(value)
		if err != nil {
			return fmt.Errorf("invalid MCP server URL %q: %w", value, err)
		}
		if parsed.Scheme != "http" && parsed.Scheme != "https" {
			return fmt.Errorf("MCP server URL must use http or https scheme, got %q", parsed.Scheme)
		}
		if parsed.Host == "" {
			return fmt.Errorf("MCP server URL %q must include a host", value)
		}
		entry.URL = value
	case "headers":
		parsed, err := parseMCPHeaders(value)
		if err != nil {
			return fmt.Errorf("invalid headers for %s: %w", key, err)
		}
		entry.Headers = parsed
	case "tools":
		var tools []string
		if err := json.Unmarshal([]byte(value), &tools); err != nil {
			return fmt.Errorf("invalid JSON array for %s: %w", key, err)
		}
		seen := make(map[string]struct{}, len(tools))
		filtered := make([]string, 0, len(tools))
		for _, t := range tools {
			if t == "" {
				return fmt.Errorf("tool names in %s must not be empty", key)

View on GitHub (pinned to 5cf97d0d15)

Solutions

1. Include the hostname (and port if needed) after the scheme: https://mcp.example.com/sse
2. Re-copy the complete URL from the server documentation
3. Check templated/scripted values so the host placeholder is filled

Example fix

// before
ocr config set mcp_servers.api.url https:///api/mcp
// after
ocr config set mcp_servers.api.url https://mcp.example.com/api/mcp

u, err := url.Parse(rawURL)
if err != nil || u.Host == "" {
	return fmt.Errorf("URL must include a host")
}

func hasHost(rawURL string) bool {
	u, err := url.Parse(rawURL)
	return err == nil && u.Host != ""
}

if err := setMCPServerValue(cfg, key, value); err != nil {
	fmt.Fprintf(os.Stderr, "config set failed: %v\n", err)
	os.Exit(1)
}

When it happens

Trigger: Calling setMCPServerValue with field "url" where the URL has a valid http/https scheme but no host, e.g. "http://" or "https:///api/mcp".

Common situations: Truncated paste of a URL losing the hostname; templated URLs where the host variable was empty; mistyping extra slashes after the scheme.

Understand the failure class

Background: "Invalid URL" / "URL cannot be empty": fix the malformed or missing URL behind request-construction failures — this error's family across 50 libraries.

Related errors

• MCP server URL cannot be empty
• invalid MCP server URL %q: %w
• MCP server URL must use http or https scheme, got %q
• invalid URL for %s: %w
• invalid MCP server key %q: expected mcp_servers.<name>.<fiel

AI-assisted analysis of alibaba/open-code-review@5cf97d0d15 (2026-09-02). Data as JSON: /api/errors/772dcbc3ae1ff808. Report an issue: GitHub.