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

Add a descriptive `description` to the tool entry in tools.yaml.

description is required for tool %q

Error message

description is required for tool %q

What it means

looker-get-project-file Config.Initialize requires a non-empty description. Because the description is published in the MCP manifest consumed by LLM clients, an empty description makes the tool config invalid and initialization aborts with this error.

Source

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

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

	// 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

View on GitHub (pinned to 8cc6e09de2)

Solutions

Add a descriptive `description` to the tool entry in tools.yaml.
Verify indentation so description is a child of the tool.
Set Description programmatically before calling Initialize.
Run `toolbox validate` to catch missing descriptions pre-deploy.

Example fix

// before
  get-project-file:
    kind: looker-get-project-file
    source: my-looker
// after
  get-project-file:
    kind: looker-get-project-file
    source: my-looker
    description: Fetches the contents of a file within a Looker project.

Defensive patterns

Strategy: validation

Validate before calling

if strings.TrimSpace(cfg.Description) == "" {
    return errors.New("tool 'get-project-file': description is required")
}

Try / catch

tool, err := cfg.Initialize(ctx)
if err != nil {
    log.Fatalf("invalid looker-get-project-file config: %v", err)
}

Prevention

Always include a description for looker-get-project-file entries.
Use `toolbox validate` pre-deploy to catch empty fields.
Watch YAML indentation when adding tool fields.
Reject blank description strings in config generators.

When it happens

Trigger: tools.yaml declares a looker-get-project-file tool without `description`, or Go code builds the Config with an empty Description and calls Initialize.

Common situations: Missing YAML field; wrong indentation placing description outside the tool block; templating leaving the field blank.

Related errors

AI-assisted analysis of googleapis/mcp-toolbox@8cc6e09de2 (2026-09-05). Data as JSON: /api/errors/9b92704040fbc4d9. Report an issue: GitHub.