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

Add a non-empty `description:` to the firestore-query tool config.

description is required for tool %q

Error message

description is required for tool %q

What it means

Config.Initialize for firestore-query rejects configs lacking a description. The description is mandatory MCP metadata; Initialize returns this error before parameter setup (including the default limit) when cfg.Description is empty.

Source

Thrown at internal/tools/firestore/firestorequery/firestorequery.go:91

	AnalyzeQuery   bool           `yaml:"analyzeQuery"` // Analyze query (boolean, not parameterizable)

	// Parameters for template substitution
	Parameters  parameters.Parameters  `yaml:"parameters"`
	Annotations *tools.ToolAnnotations `yaml:"annotations,omitempty"`
}

// validate interface
var _ tools.ToolConfig = Config{}

// ToolConfigType returns the type of tool configuration
func (cfg Config) ToolConfigType() string {
	return resourceType
}

// Initialize creates a new Tool instance from the configuration
func (cfg Config) Initialize(context.Context) (tools.Tool, error) {
	if cfg.Description == "" {
		return nil, fmt.Errorf("description is required for tool %q", cfg.Name)
	}

	// Set default limit if not specified
	if cfg.Limit == "" {
		cfg.Limit = fmt.Sprintf("%d", defaultLimit)
	}

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

// validate interface

View on GitHub (pinned to 8cc6e09de2)

Solutions

Add a non-empty `description:` to the firestore-query tool config.
Ensure any env-var interpolation for description yields a non-empty value.

Example fix

// before
  query:
    kind: firestore-query
    source: my-fs
// after
  query:
    kind: firestore-query
    source: my-fs
    description: Run a query against a Firestore collection with filters and ordering

Defensive patterns

Strategy: validation

Validate before calling

if strings.TrimSpace(cfg.Description) == "" {
	return errors.New("firestore-query tool requires a non-empty description")
}

Try / catch

tool, err := cfg.Initialize(ctx)
if err != nil {
	return fmt.Errorf("invalid firestore-query config: %w", err)
}

Prevention

Always author a meaningful description alongside filters/limit config.
Automate a schema check on tool YAML requiring `description`.
Treat tool init errors as config errors, not runtime errors, in alerting.

When it happens

Trigger: A firestore-query tool config with no `description:` field or an empty string value.

Common situations: Configs generated from templates where description was left blank; users assuming optional fields are all optional.

Related errors

AI-assisted analysis of googleapis/mcp-toolbox@8cc6e09de2 (2026-09-05). Data as JSON: /api/errors/f00bb00d81cf38c5. Report an issue: GitHub.