googleapis/mcp-toolbox · error

error executing script template: %w

Error message

error executing script template: %w

What it means

`generateScriptContent` throws "error executing script template: %w" when the parsed `nodeScriptTemplate` fails during `tmpl.Execute(&buf, data)` while rendering the Node wrapper script with the tool data (name, parameters, toolbox version, optional vars). Parse succeeded; rendering against the provided `data` struct failed, typically because a template action dereferences a missing/nil value or a method returns an error.

Source

Thrown at cmd/internal/skills/generator.go:273

// (using a generated config) and arguments to execute the specific tool.
func generateScriptContent(name string, configArgs string, licenseHeader string, mode string, version string, optionalVars []string) (string, error) {
	data := scriptData{
		Name:           name,
		ConfigArgs:     configArgs,
		LicenseHeader:  licenseHeader,
		InvocationMode: mode,
		ToolboxVersion: version,
		OptionalVars:   optionalVars,
	}

	tmpl, err := template.New("script").Parse(nodeScriptTemplate)
	if err != nil {
		return "", fmt.Errorf("error parsing script template: %w", err)
	}

	var buf strings.Builder
	if err := tmpl.Execute(&buf, data); err != nil {
		return "", fmt.Errorf("error executing script template: %w", err)
	}

	return buf.String(), nil
}

// formatParameters converts a list of parameter manifests into a formatted JSON schema string.
// This schema is used in the skill documentation to describe the input parameters for a tool.
func formatParameters(params []parameters.ParameterManifest, envVars map[string]string) (string, error) {
	if len(params) == 0 {
		return "", nil
	}

	var sb strings.Builder
	sb.WriteString("#### Parameters\n\n")
	sb.WriteString("| Name | Type | Description | Required | Default |\n")
	sb.WriteString("| :--- | :--- | :--- | :--- | :--- |\n")

	for _, p := range params {

View on GitHub (pinned to 8cc6e09de2)

Solutions

1. Read the wrapped execution error — it names the failing template node and line
2. Verify every field referenced in `nodeScriptTemplate` exists on the script data struct and is non-nil where used
3. Add `{{ if }}` guards around optional fields (optionalVars, parameters) in the template
4. Reproduce with the failing tool's manifest in a unit test for generateScriptContent

Example fix

// before (template): {{ range .OptionalVars }}{{ . }}{{ end }} on nil slice
// after (template): {{ if .OptionalVars }}{{ range .OptionalVars }}{{ . }}{{ end }}{{ end }}

// Normalize inputs before rendering
if optionalVars == nil { optionalVars = map[string]string{} }
if params == nil { params = []map[string]any{} }

var buf strings.Builder
if err := tmpl.Execute(&buf, data); err != nil {
	return "", fmt.Errorf("error executing script template: %w", err)
}

When it happens

Trigger: `tmpl.Execute(&buf, data)` is called with the script data struct and a field/method used in `nodeScriptTemplate` fails — e.g. ranging over a nil parameters slice, calling a method that returns an error, or a field renamed in the data struct that the template still references.

Common situations: A tool manifest with nil/empty parameters fed into the template after a refactor changed the data struct fields; template actions reference fields removed from the script data struct; version/optionalVars fields unset where the template assumes values.

Related errors

• error parsing script template: %w
• error parsing markdown template: %w
• error executing markdown template: %w
• error parsing URL: %s
• error replacing pathParams: %s

AI-assisted analysis of googleapis/mcp-toolbox@8cc6e09de2 (2026-09-05). Data as JSON: /api/errors/b00bffebb399b916. Report an issue: GitHub.