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

Add a non-empty description field to the tool's YAML config

description is required for tool %q

Error message

description is required for tool %q

What it means

This error is thrown by Config.Initialize when a cloudhealthcare-get-dicom-store tool is defined without a non-empty description. The toolbox requires every tool to carry a human-readable description so agents/LLMs know what the tool does. Initialization fails fast rather than registering an undescribed tool.

Source

Thrown at internal/tools/cloudhealthcare/cloudhealthcaregetdicomstore/cloudhealthcaregetdicomstore.go:69

}

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 := buildParams(false)
	return Tool{
		BaseTool: tools.NewBaseTool(
			cfg,
			tools.GetAnnotationsOrDefault(cfg.Annotations, tools.NewReadOnlyAnnotations),
			tools.Manifest{Description: cfg.Description, Parameters: params.Manifest(), AuthRequired: cfg.AuthRequired},
			params,
		),
	}, nil
}

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

type Tool struct {
	tools.BaseTool[Config]

View on GitHub (pinned to 8cc6e09de2)

Solutions

Add a non-empty description field to the tool's YAML config
Set cfg.Description programmatically before calling Initialize
Validate the config early in startup so the failure points at the right file

Example fix

# before
tools:
  get_dicom_store:
    kind: cloud-healthcare-get-dicom-store
# after
tools:
  get_dicom_store:
    kind: cloud-healthcare-get-dicom-store
    description: Fetches a DICOM store from Cloud Healthcare API

Defensive patterns

Strategy: validation

Validate before calling

if cfg.Description == "" {
    return fmt.Errorf("tool %q is missing a description", cfg.Name)
}

Prevention

Always include a description field in every tool YAML block
Add a CI lint that parses tool configs and asserts description is non-empty
Use config structs with required-field validation before Initialize

When it happens

Trigger: Calling Initialize on a Config whose Description field is the empty string (omitted in YAML config or set to "").

Common situations: YAML tool definitions that omit the description field; programmatic construction of Config that leaves Description unset; tooling that copies a config and drops the description.

Related errors

AI-assisted analysis of googleapis/mcp-toolbox@8cc6e09de2 (2026-09-05). Data as JSON: /api/errors/90791b2158761bba. Report an issue: GitHub.