googleapis/mcp-toolbox · error

description is required for tool %q

Error message

description is required for tool %q

What it means

LookerGetProjectFiles.Config.Initialize validates that a non-empty description was supplied, because the description becomes the tool's LLM-facing manifest text. When Config.Description is empty, Initialize returns this error and the tool is not created. It is a YAML/config validation failure at load time.

Source

Thrown at internal/tools/looker/lookergetprojectfiles/lookergetprojectfiles.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)
	}

	projectIdParameter := parameters.NewStringParameter("project_id", "The id of the project containing the files")
	allParameters := parameters.Parameters{projectIdParameter}

	// finish tool setup
	return Tool{
		BaseTool: tools.NewBaseTool(
			cfg,
			tools.GetAnnotationsOrDefault(cfg.Annotations, tools.NewReadOnlyAnnotations),
			tools.Manifest{Description: cfg.Description, Parameters: allParameters.Manifest(), AuthRequired: cfg.AuthRequired},
			allParameters,
		),
	}, nil
}

// validate interface
var _ tools.Tool = Tool{}

View on GitHub (pinned to 8cc6e09de2)

Solutions

1. Add a descriptive `description:` string to the looker-get-project-files tool entry in your YAML.
2. Write the description from the calling agent's perspective (what the tool does, when to use it).
3. Re-run the toolbox; if it still fails, check that the tool name in the error matches the entry you edited.

Example fix

// before
tools:
  get-project-files:
    kind: looker-get-project-files
    source: my-looker
// after
tools:
  get-project-files:
    kind: looker-get-project-files
    source: my-looker
    description: Lists all files in a given Looker project

// Pre-load YAML and assert required tool fields
var raw map[string]map[string]any
yaml.Unmarshal(cfgBytes, &raw)
for name, t := range raw["tools"] {
    if t["kind"] == "looker-get-project-files" {
        desc, _ := t["description"].(string)
        if desc == "" {
            return fmt.Errorf("tool %q (looker-get-project-files) is missing a non-empty description", name)
        }
    }
}

tool, err := toolCfg.Initialize(ctx)
if err != nil && strings.Contains(err.Error(), "description is required") {
    return fmt.Errorf("config error: add a 'description' to tool %q in your YAML: %w", toolCfg.Name, err)
}

When it happens

Trigger: A tools.yaml entry of kind looker-get-project-files omits the `description` field (or sets it to an empty string), causing Config.Initialize to fail while the toolbox config is being loaded.

Common situations: Hand-writing tool configs and skipping description because it seems optional; templated config generation that leaves description blank; upgrading from an older config format where description was defaulted.

Understand the failure class

Background: "missing required argument" and "the following required arguments were not provided": what required-argument errors mean and how to fix them — this error's family across 20 libraries.

Related errors

• description is required for tool %q
• unable to parse Timeout string as time.Duration: %s
• description is required for tool %q
• description is required for tool %q
• description is required for tool %q

AI-assisted analysis of googleapis/mcp-toolbox@8cc6e09de2 (2026-09-05). Data as JSON: /api/errors/95d65b7d9be6b159. Report an issue: GitHub.