googleapis/mcp-toolbox · error

error parsing base URL: %s

Error message

error parsing base URL: %s

What it means

getURL parses the source's HttpBaseURL() with net/url.Parse before resolving the relative path. If the base URL string is not a parseable URL, the parse error is wrapped as "error parsing base URL" and Invoke fails with an agent error.

Source

Thrown at internal/tools/http/http.go:191

				return ""
			}
			return url.QueryEscape(fmt.Sprintf("%v", v))
		},
	}

	templ, err := template.New("url").Funcs(funcMap).Parse(path)
	if err != nil {
		return "", fmt.Errorf("error parsing URL: %s", err)
	}
	var templatedPath bytes.Buffer
	err = templ.Execute(&templatedPath, pathParamsMap)
	if err != nil {
		return "", fmt.Errorf("error replacing pathParams: %s", err)
	}

	baseParsedURL, err := url.Parse(baseURL)
	if err != nil {
		return "", fmt.Errorf("error parsing base URL: %s", err)
	}
	if baseParsedURL.Scheme == "" || baseParsedURL.Host == "" {
		return "", fmt.Errorf("base URL must include scheme and host")
	}

	relativePath := templatedPath.String()
	relParsedURL, err := url.Parse(relativePath)
	if err != nil {
		return "", fmt.Errorf("error parsing URL path: %s", err)
	}
	if relParsedURL.Scheme != "" || relParsedURL.Host != "" || relParsedURL.User != nil {
		return "", fmt.Errorf("path must be relative and cannot override base host")
	}

	// Reject dot segments before resolution
	for _, segment := range strings.Split(relParsedURL.Path, "/") {
		if segment == ".." {
			return "", fmt.Errorf("path cannot contain dot segments (..)")

View on GitHub (pinned to 8cc6e09de2)

Solutions

1. Fix the source's "baseUrl" in tools.yaml so it is a valid absolute URL.
2. Check the environment variable or secret substituted into baseUrl for stray spaces/quotes.
3. Add a startup validation that url.Parse succeeds on every http source's baseUrl before serving.

Example fix

# before
baseUrl: "http://api.example.com/%zz"
# after
baseUrl: "https://api.example.com"

// Validate baseUrl when defining the source
if _, err := url.Parse(strings.TrimSpace(os.Getenv("API_BASE_URL"))); err != nil {
    return fmt.Errorf("invalid API_BASE_URL: %w", err)
}

urlString, err := getURL(baseURL, path, pathParams, queryParams, defaultQuery, paramsMap)
if err != nil {
    if strings.HasPrefix(err.Error(), "error parsing base URL") {
        return nil, fmt.Errorf("source baseUrl %q is not a valid URL: %w", baseURL, err)
    }
    return nil, err
}

When it happens

Trigger: The http source's baseUrl config value is malformed — contains spaces, control characters, or invalid percent-encodings like "http://api.example.com/%zz" — causing url.Parse to fail during Invoke.

Common situations: Env-var-substituted base URLs with stray whitespace or quotes; truncated URLs in YAML; invalid percent-encoding after string interpolation.

Understand the failure class

Background: "Invalid URL" errors: why new URL(), URI.parse, and reqwest::Url reject your string — missing scheme, whitespace, and bad path format — this error's family across 39 libraries.

Related errors

• base URL must include scheme and host
• invalid auth URL
• error creating request: %w
• failed to create request: %w
• description is required for tool %q

AI-assisted analysis of googleapis/mcp-toolbox@8cc6e09de2 (2026-09-05). Data as JSON: /api/errors/a231438c708e51c4. Report an issue: GitHub.