googleapis/mcp-toolbox · error

error creating go template %s

Error message

error creating go template %s

What it means

ResolveTemplateParams wraps text/template's Parse failure with this message. The configured statement/URL/message is not syntactically valid Go template syntax — typically unbalanced braces or invalid template tokens. This fails before any parameter values are substituted.

Source

Thrown at internal/util/parameters/parameters.go:291

		}
		resultParamValues = append(resultParamValues, ParamValue{Name: k, Value: v})
	}
	return resultParamValues, nil
}

func ResolveTemplateParams(templateParams Parameters, originalStatement string, paramsMap map[string]any) (string, error) {
	templateParamsValues, err := GetParams(templateParams, paramsMap)
	templateParamsMap := templateParamsValues.AsMap()
	if err != nil {
		return "", fmt.Errorf("error getting template params %s", err)
	}

	funcMap := template.FuncMap{
		"array": ConvertArrayParamToString,
	}
	t, err := template.New("statement").Funcs(funcMap).Parse(originalStatement)
	if err != nil {
		return "", fmt.Errorf("error creating go template %s", err)
	}
	var result bytes.Buffer
	err = t.Execute(&result, templateParamsMap)
	if err != nil {
		return "", fmt.Errorf("error executing go template %s", err)
	}

	modifiedStatement := result.String()
	return modifiedStatement, nil
}

// ProcessParameters concatenate templateParameters and parameters from a tool.
// It returns a list of concatenated parameters, concatenated Toolbox manifest, and concatenated MCP Manifest.
func ProcessParameters(templateParams Parameters, params Parameters) (Parameters, []ParameterManifest, error) {
	allParameters := slices.Concat(params, templateParams)

	// verify no duplicate parameter names
	err := CheckDuplicateParameters(allParameters)

View on GitHub (pinned to 8cc6e09de2)

Solutions

1. Locate the {{...}} expression cited in the wrapped error and balance/fix the braces.
2. Use only Go template syntax: {{.paramName}} and the provided {{array .paramName}} helper.
3. Escape or remove literal {{ sequences in the statement that weren't meant as templates.
4. Validate the statement offline with template.New("statement").Parse before deploying the config.

Example fix

# before (Jinja-style, invalid in Go)
SELECT * FROM t LIMIT {{ limit }}

# after (Go template syntax)
SELECT * FROM t LIMIT {{.limit}}

if _, err := template.New("s").Funcs(template.FuncMap{"array": params.ConvertArrayParamToString}).Parse(stmt); err != nil {
    return fmt.Errorf("invalid template in statement: %w", err)
}

out, err := params.ResolveTemplateParams(tp, stmt, m)
if err != nil && strings.Contains(err.Error(), "error creating go template") {
    return fmt.Errorf("statement has invalid Go template syntax: %w", err)
}

When it happens

Trigger: A configured statement containing malformed template syntax: unclosed {{, stray braces, invalid pipeline syntax, or syntax from other template languages (Jinja/Handlebars) that Go's parser rejects.

Common situations: Hand-edited SQL or YAML introducing literal {{; copying templates from non-Go docs; leftover {{ limit }} style syntax from Jinja; accidental use of undefined helper names at parse time.

Related errors

• error substituting params for message: %w
• error parsing template '%s': %w
• error executing go template %s
• error embedding parameters: %w
• failed to check auth requirements: %w

AI-assisted analysis of googleapis/mcp-toolbox@8cc6e09de2 (2026-09-05). Data as JSON: /api/errors/a7d6a5ea765f21f6. Report an issue: GitHub.