googleapis/mcp-toolbox · error

error replacing pathParams: %s

Error message

error replacing pathParams: %s

What it means

After parsing the path template, getURL executes it against the resolved path-param values; if templ.Execute fails (e.g., the template references a missing map key with a raising option or an action returns an error), the failure is wrapped as this error during Invoke.

Source

Thrown at internal/tools/http/http.go:186

		"queryEscape": func(v any) string {
			if s, ok := v.(string); ok {
				return url.QueryEscape(s)
			}
			if v == nil {
				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")
	}

View on GitHub (pinned to 8cc6e09de2)

Solutions

1. Verify every {{.name}} reference in the tool's path matches a declared pathParams entry exactly (case-sensitive).
2. Make required path params non-nil and correctly typed before invocation.
3. Guard templates with {{if}} or default handling ({{.x | default}}) for optional values.

Example fix

// before
path: "/users/{{.userId}}" // pathParams declares "id"
// after
path: "/users/{{.id}}"

// Ensure every template reference in path has a matching pathParam
for _, name := range extractTemplateRefs(tool.Path) {
    if !pathParams.Contains(name) {
        return fmt.Errorf("path references %q which is not declared in pathParams", name)
    }
}

urlString, err := getURL(baseURL, path, pathParams, queryParams, defaultQuery, paramsMap)
if err != nil {
    if strings.HasPrefix(err.Error(), "error replacing pathParams") {
        return nil, fmt.Errorf("failed to render path params into %q: %w", path, err)
    }
    return nil, err
}

When it happens

Trigger: The path template calls a function or accesses data that fails at execution time — e.g., {{.missing | pathEscape}} on a nil/absent path param value, or a custom func invoked with invalid input — during Invoke of an http tool.

Common situations: Path declared in "pathParams" but the LLM supplied a wrong-typed value; template referencing a param name that doesn't exist in pathParams; nil values flowing into pathEscape.

Related errors

• error parsing URL: %s
• error parsing URL path: %s
• failed to create request: %w
• error parsing base URL: %s
• base URL must include scheme and host

AI-assisted analysis of googleapis/mcp-toolbox@8cc6e09de2 (2026-09-05). Data as JSON: /api/errors/afd08a084cae38e7. Report an issue: GitHub.