What causes "description is required for tool %q" in googleapis/mcp-toolbox?

Add a descriptive `description:` string to the tool entry

description is required for tool %q

Error message

description is required for tool %q

What it means

Initialize for the looker-update-dashboard-element tool rejects configs with an empty `description`. The description is mandatory because it is exposed to MCP clients as the tool's usage documentation; registration is aborted with this error otherwise.

Source

Thrown at internal/tools/looker/lookerupdatedashboardelement/lookerupdatedashboardelement.go:72

}

type Config struct {
	tools.ConfigBase `yaml:",inline"`
	Type             string                 `yaml:"type" validate:"required"`
	Source           string                 `yaml:"source" validate:"required"`
	Annotations      *tools.ToolAnnotations `yaml:"annotations,omitempty"`
}

// validate interface
var _ tools.ToolConfig = Config{}

func (cfg Config) ToolConfigType() string {
	return resourceType
}

func (cfg Config) Initialize(context.Context) (tools.Tool, error) {
	if cfg.Description == "" {
		return nil, fmt.Errorf("description is required for tool %q", cfg.Name)
	}

	params := lookercommon.GetQueryParameters()

	dashboardIdParam := parameters.NewStringParameter("dashboard_id", "The ID of the dashboard containing the element.")
	params = append(params, dashboardIdParam)
	elementIdParam := parameters.NewStringParameter("dashboard_element_id", "The ID of the dashboard element to update.")
	params = append(params, elementIdParam)
	titleParam := parameters.NewStringParameter("title", "The new title of the element.", parameters.WithStringDefault(""))
	params = append(params, titleParam)
	visConfigParam := parameters.NewMapParameter("vis_config", "The new visualization configuration.", "", parameters.WithMapDefault(map[string]any{}))
	params = append(params, visConfigParam)

	dashFilters := parameters.NewArrayParameter(
		"dashboard_filters",
		`An array of dashboard filters like [{"dashboard_filter_name": "name", "field": "view_name.field_name"}, ...]`,
		parameters.NewMapParameter(
			"dashboard_filter",

View on GitHub (pinned to 8cc6e09de2)

Solutions

Add a descriptive `description:` string to the tool entry
Fix the generating template so description is always emitted
Pre-validate configs for required fields before server start

Example fix

// before
tools:
  update_dashboard_element:
    kind: looker-update-dashboard-element
    source: my-looker-source
// after
tools:
  update_dashboard_element:
    kind: looker-update-dashboard-element
    source: my-looker-source
    description: Update a dashboard element's properties in Looker.

Defensive patterns

Strategy: validation

Validate before calling

if cfg.Description == "" {
    return errors.New("looker-update-dashboard-element tool requires a non-empty description")
}

Try / catch

tool, err := cfg.Initialize(ctx)
if err != nil {
    if strings.Contains(err.Error(), "description is required") {
        return fmt.Errorf("add `description` to tool %q in tools.yaml", cfg.Name)
    }
    return err
}

Prevention

Add a schema check in CI that every tool entry has a non-empty description
Use config templates that require description explicitly
Review diffs of tools.yaml for removed description lines

When it happens

Trigger: A tool definition of kind looker-update-dashboard-element lacks `description:` (or it is empty string) when Initialize runs during config load.

Common situations: Omitting description while hand-editing tools.yaml; config generators dropping empty fields; copying a tool block and deleting the description line.

Related errors

AI-assisted analysis of googleapis/mcp-toolbox@8cc6e09de2 (2026-09-05). Data as JSON: /api/errors/e112807e68815bd5. Report an issue: GitHub.