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

Add a meaningful `description` to the tool definition in YAML.

description is required for tool %q

Error message

description is required for tool %q

What it means

Config.Initialize for clickhouse-list-tables requires a non-empty `description`; the toolbox surfaces tool descriptions to MCP/LLM clients, so an empty one is rejected at load time. This is config validation, not a runtime failure.

Source

Thrown at internal/tools/clickhouse/clickhouselisttables/clickhouselisttables.go:75

}

type Config struct {
	tools.ConfigBase `yaml:",inline"`
	Type             string                 `yaml:"type" validate:"required"`
	Source           string                 `yaml:"source" validate:"required"`
	Parameters       parameters.Parameters  `yaml:"parameters"`
	Annotations      *tools.ToolAnnotations `yaml:"annotations,omitempty"`
}

var _ tools.ToolConfig = Config{}

func (cfg Config) ToolConfigType() string {
	return listTablesType
}

func (cfg Config) Initialize(context.Context) (tools.Tool, error) {
	if cfg.Description == "" {
		return nil, fmt.Errorf("description is required for tool %q", cfg.Name)
	}

	databaseParameter := parameters.NewStringParameter(databaseKey, "The database to list tables from.")
	params := parameters.Parameters{databaseParameter}

	allParameters, paramManifest, err := parameters.ProcessParameters(nil, params)
	if err != nil {
		return nil, err
	}

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

View on GitHub (pinned to 8cc6e09de2)

Solutions

Add a meaningful `description` to the tool definition in YAML.
Verify the description key is correctly indented under the right tool.
Set cfg.Description before Initialize when constructing Config in code.

Example fix

// before
tools:
  list_tables:
    source: ch
// after
tools:
  list_tables:
    source: ch
    description: List tables in a ClickHouse database.

Defensive patterns

Strategy: validation

Validate before calling

// Go
if cfg.Name == "" || cfg.Description == "" {
    return errors.New("clickhouse-list-tables needs name and description")
}
_, err := cfg.Initialize(context.Background())

Prevention

Use a config template that includes description for every tool.
Verify YAML indentation places description inside the intended tool block.
Run config-load smoke tests in CI.

When it happens

Trigger: A `clickhouse-list-tables` tool entry in YAML without a `description` (or with an empty/misspelled key), or a Config literal with Description unset passed to Initialize in Go tests.

Common situations: Trimming configs for brevity and dropping the description; YAML indentation putting the description under the wrong tool; renaming keys during upgrades.

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/b2f36d774b59fdfc. Report an issue: GitHub.