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

Add a non-empty description field to the looker-deleteagent tool entry

description is required for tool %q

Error message

description is required for tool %q

What it means

Initialize for the looker-deleteagent tool validates that the Config carries a non-empty Description. The description populates the tool's MCP manifest for LLM clients; an empty description means the tool definition is invalid and initialization returns this error.

Source

Thrown at internal/tools/looker/lookerdeleteagent/lookerdeleteagent.go:71

}

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)
	}

	agentIdParameter := parameters.NewStringParameter("agent_id", "The ID of the agent.", parameters.WithStringDefault(""))
	params := parameters.Parameters{agentIdParameter}

	annotations := &tools.ToolAnnotations{}
	if cfg.Annotations != nil {
		*annotations = *cfg.Annotations
	}
	readOnlyHint := false
	destructiveHint := true
	annotations.ReadOnlyHint = &readOnlyHint
	annotations.DestructiveHint = &destructiveHint

	return Tool{
		BaseTool: tools.NewBaseTool(
			cfg,
			annotations,

View on GitHub (pinned to 8cc6e09de2)

Solutions

Add a non-empty description field to the looker-deleteagent tool entry
Check the rendered config to ensure the description didn't resolve to empty
Set Description when building lookerdeleteagent.Config programmatically

Example fix

# before
tools:
  delete-agent:
    kind: looker-delete-agent
    source: my-looker
# after
tools:
  delete-agent:
    kind: looker-delete-agent
    source: my-looker
    description: Deletes a Looker agent by ID

Defensive patterns

Strategy: validation

Validate before calling

if strings.TrimSpace(cfg.Description) == "" {
    return fmt.Errorf("looker-delete-agent requires a description")
}

Type guard

func validDescription(cfg lookerdeleteagent.Config) bool {
    return strings.TrimSpace(cfg.Description) != ""
}

Try / catch

tool, err := cfg.Initialize(ctx)
if err != nil {
    if strings.Contains(err.Error(), "description is required") {
        // populate cfg.Description and retry
    }
    return err
}

Prevention

Always set description in tool YAML entries
Fail fast with a config linter on empty descriptions
Give template variables for description non-empty defaults
Verify rendered configs in CI before deployment

When it happens

Trigger: A looker-deleteagent entry in the tools YAML lacks description or has an empty value when Initialize runs during server startup or config parsing.

Common situations: Hand-written config missing the description key; templated config where the variable was empty; bulk-edited YAML where descriptions were dropped.

Related errors

AI-assisted analysis of googleapis/mcp-toolbox@8cc6e09de2 (2026-09-05). Data as JSON: /api/errors/23ad19467aadb890. Report an issue: GitHub.