googleapis/mcp-toolbox · error

bucket cannot be empty for tool %q

Error message

bucket cannot be empty for tool %q

What it means

This error is thrown by the cloudstorage-get-bucket-iam-policy tool's Config.Initialize when a bucket name was provided (the `bucket` field is non-nil) but its value is an empty string. The toolbox validates tool configs at startup so misconfigured tools fail fast instead of at invocation time. An empty pointer-deref'd bucket means the YAML config set `bucket: ""` or the programmatic config passed `tools.Ptr("")`.

Source

Thrown at internal/tools/cloudstorage/cloudstoragegetbucketiampolicy/cloudstoragegetbucketiampolicy.go:71

	tools.ConfigBase `yaml:",inline"`
	Type             string                 `yaml:"type" validate:"required"`
	Source           string                 `yaml:"source" validate:"required"`
	Annotations      *tools.ToolAnnotations `yaml:"annotations,omitempty"`
	Bucket           *string                `yaml:"bucket,omitempty"`
}

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)
	}
	if cfg.Bucket != nil && *cfg.Bucket == "" {
		return nil, fmt.Errorf("bucket cannot be empty for tool %q", cfg.Name)
	}

	allParameters := parameters.Parameters{}
	if cfg.Bucket == nil {
		allParameters = append(allParameters, parameters.NewStringParameter(bucketKey, "Name of the Cloud Storage bucket whose IAM policy should be returned."))
	}

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

var _ tools.Tool = Tool{}

View on GitHub (pinned to 8cc6e09de2)

Solutions

1. Set a real bucket name in the tool config, e.g. `bucket: my-bucket`.
2. If the bucket should come from the model at invocation time, remove the `bucket` field entirely so it becomes a required tool parameter.
3. Validate config values (check for empty strings after env substitution) before calling Initialize.

Example fix

# before
bucket: ""
description: Get IAM policy
# after
bucket: my-gcs-bucket
description: Get IAM policy

if cfg.Bucket != nil && *cfg.Bucket == "" {
    return fmt.Errorf("bucket cannot be empty for tool %q; set a name or omit the field", cfg.Name)
}

func hasBucket(cfg Config) bool { return cfg.Bucket != nil && *cfg.Bucket != "" }

When it happens

Trigger: Initializing a cloudstorage-get-bucket-iam-policy tool where cfg.Bucket != nil and *cfg.Bucket == "" — e.g. YAML `bucket: ""` or code passing an empty-string pointer as a fixed bucket.

Common situations: Templated configs where a placeholder was substituted with an empty value; env-var expansion producing an empty string; hand-edited YAML leaving the bucket value blank.

Related errors

• bucket cannot be empty for tool %q
• bucket cannot be empty for tool %q
• invalid source for %q tool: source %q is not a compatible ty
• description is required for tool %q
• description is required for tool %q

AI-assisted analysis of googleapis/mcp-toolbox@8cc6e09de2 (2026-09-05). Data as JSON: /api/errors/d18fe0cd7db222ad. Report an issue: GitHub.