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

Add a `description` line to the looker-get-dimensions tool entry.

description is required for tool %q

Error message

description is required for tool %q

What it means

looker-get-dimensions Config.Initialize rejects configurations missing a description. The description is published in the MCP tool manifest so clients know what the tool does; an empty description makes initialization fail with this error.

Source

Thrown at internal/tools/looker/lookergetdimensions/lookergetdimensions.go:73

}

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 := lookercommon.GetFieldParameters()

	// finish tool setup
	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{}

View on GitHub (pinned to 8cc6e09de2)

Solutions

Add a `description` line to the looker-get-dimensions tool entry.
Verify YAML indentation so the field belongs to the tool block.
Set Description before Initialize when constructing configs in code.
Run `toolbox validate` before deployment.

Example fix

// before
  get-dimensions:
    kind: looker-get-dimensions
    source: my-looker
// after
  get-dimensions:
    kind: looker-get-dimensions
    source: my-looker
    description: Retrieves LookML dimension fields for a Looker Explore.

Defensive patterns

Strategy: validation

Validate before calling

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

Try / catch

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

Prevention

Include a description for every looker-get-dimensions entry.
Add `toolbox validate` to CI pipelines.
Check YAML indentation when editing nested tool blocks.
Set Description explicitly when building Config structs in code.

When it happens

Trigger: Declaring a looker-get-dimensions tool in tools.yaml without `description`, or building the Config in Go with an empty Description and calling Initialize.

Common situations: Omitted YAML field; description nested at the wrong indentation; automated config generators producing empty strings.

Related errors

AI-assisted analysis of googleapis/mcp-toolbox@8cc6e09de2 (2026-09-05). Data as JSON: /api/errors/54c886b94d3be576. Report an issue: GitHub.