googleapis/mcp-toolbox · error

description is required for tool %q

Error message

description is required for tool %q

What it means

Config.Initialize for the cloudhealthcare-retrieve-rendered-dicom-instance tool requires a non-empty description. Descriptions are surfaced to the LLM as the tool's description in the MCP manifest; without one the tool would be unusable/undescribable, so initialization fails fast with this error.

Source

Thrown at internal/tools/cloudhealthcare/cloudhealthcareretrieverendereddicominstance/cloudhealthcareretrieverendereddicominstance.go:74

}

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

  1. Add a description field to the tool entry in tools.yaml
  2. Check YAML indentation so description lands under the tool config, not a sibling key
  3. If constructing Config in code, set cfg.Description before calling Initialize

Example fix

// before (tools.yaml)
tools:
  retrieve-rendered-dicom-instance:
    kind: cloudhealthcare-retrieve-rendered-dicom-instance
    source: my-healthcare-source
// after
tools:
  retrieve-rendered-dicom-instance:
    kind: cloudhealthcare-retrieve-rendered-dicom-instance
    source: my-healthcare-source
    description: Retrieves a rendered (image/png) DICOM instance from a Cloud Healthcare DICOM store
Defensive patterns

Strategy: validation

Validate before calling

// validate the tools.yaml entry before loading
cfg, err := config.ParseYaml(yamlBytes)
if err != nil {
	log.Fatal(err)
}
for name, toolCfg := range cfg.Tools {
	if toolCfg["description"] == "" {
		log.Fatalf("tool %q is missing required description", name)
	}
}

Try / catch

tool, err := cfg.Initialize(ctx)
if err != nil {
	if strings.Contains(err.Error(), "description is required") {
		log.Fatalf("add a description to tool in tools.yaml: %v", err)
	}
	return err
}

Prevention

When it happens

Trigger: Calling Initialize on a Config (at server startup when tools.yaml is parsed) where the tool entry has no description field or description: "".

Common situations: Writing a minimal tools.yaml entry and omitting the description field; YAML indentation errors putting description under the wrong key; programmatically constructing Config and leaving Description zero-valued.

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/8697bc7b1a44fb7e. Report an issue: GitHub.