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

Add a non-empty `description:` to the looker-delete-projectdirectory tool definition.

description is required for tool %q

Error message

description is required for tool %q

What it means

Config.Initialize for looker-delete-projectdirectory rejects configs whose description (from the embedded tools.ConfigBase) is empty. A description is mandatory to build the MCP tool manifest, so Initialize fails fast with this error when parsing the tool config.

Source

Thrown at internal/tools/looker/lookerdeleteprojectdirectory/lookerdeleteprojectdirectory.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")
	directoryPathParameter := parameters.NewStringParameter("directory_path", "The path to delete in the project")
	params := parameters.Parameters{projectIdParameter, directoryPathParameter}

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

// validate interface

View on GitHub (pinned to 8cc6e09de2)

Solutions

Add a non-empty `description:` to the looker-delete-projectdirectory tool definition.
Verify the key is spelled `description` and resolves to non-empty (check env substitutions).
Lint generated configs to require a description per tool before server startup.

Example fix

# before
tools:
  delete-dir:
    kind: looker-delete-projectdirectory
    source: my-looker

# after
tools:
  delete-dir:
    kind: looker-delete-projectdirectory
    source: my-looker
    description: Deletes a file or directory from a Looker project

Defensive patterns

Strategy: validation

Validate before calling

// pre-flight check on decoded tool config
if cfg.Description == "" {
	return fmt.Errorf("tool %q must define a non-empty `description` field", cfg.Name)
}

Try / catch

tool, err := cfg.Initialize(ctx)
if err != nil {
	return fmt.Errorf("invalid looker-delete-projectdirectory config: %w (add a `description` field)", err)
}

Prevention

Always ship a `description:` line with each looker-delete-projectdirectory tool.
Lint YAML configs (schema or CI check) to reject tools missing description.
Ensure env-substituted descriptions do not expand to empty strings.
Spell the key exactly as `description`.

When it happens

Trigger: A looker-delete-projectdirectory tool block in the YAML lacking the `description` key or having it set to an empty string (including an unset env placeholder).

Common situations: Minimal hand-written configs omitting description; templating rendering an empty description; misspelled YAML key like `descriptions:`.

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

AI-assisted analysis of googleapis/mcp-toolbox@8cc6e09de2 (2026-09-05). Data as JSON: /api/errors/b8b69d2ed0ba3257. Report an issue: GitHub.