googleapis/mcp-toolbox · error

bucket cannot be empty for tool %q

Error message

bucket cannot be empty for tool %q

What it means

Thrown by cloudstorage-read-object Config.Initialize when the optional 'bucket' field is supplied as an empty string. When bucket is configured it must be a real GCS bucket name; otherwise remove the field so the bucket is provided per invocation.

Source

Thrown at internal/tools/cloudstorage/cloudstoragereadobject/cloudstoragereadobject.go:78

	Type             string                 `yaml:"type" validate:"required"`
	Source           string                 `yaml:"source" validate:"required"`
	Annotations      *tools.ToolAnnotations `yaml:"annotations,omitempty"`
	Bucket           *string                `yaml:"bucket,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)
	}
	if cfg.Bucket != nil && *cfg.Bucket == "" {
		return nil, fmt.Errorf("bucket cannot be empty for tool %q", cfg.Name)
	}

	objectParam := parameters.NewStringParameter(objectKey, "Full object name (path) within the bucket, e.g. 'path/to/file.txt'.")
	rangeParam := parameters.NewStringParameter(rangeKey, "Optional HTTP byte range, e.g. 'bytes=0-999' (first 1000 bytes), 'bytes=-500' (last 500 bytes), or 'bytes=500-' (from byte 500 to end). Empty reads the full object.", parameters.WithStringDefault(""))
	allParameters := parameters.Parameters{}
	if cfg.Bucket == nil {
		allParameters = append(allParameters, parameters.NewStringParameter(bucketKey, "Name of the Cloud Storage bucket containing the object."))
	}
	allParameters = append(allParameters, objectParam, rangeParam)

	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

View on GitHub (pinned to 8cc6e09de2)

Solutions

1. Remove the empty 'bucket' field from the tool config
2. Set a valid bucket name (e.g. `bucket: my-bucket`)
3. Correct the environment variable so it resolves to a non-empty bucket name

Example fix

// before
  read-object:
    kind: cloudstorage-read-object
    source: my-gcs
    description: Read object
    bucket: ""
// after
  read-object:
    kind: cloudstorage-read-object
    source: my-gcs
    description: Read object
    bucket: my-bucket

if b, exists := cfg["bucket"]; exists && (b == "" || b == nil) {
    return errors.New("bucket must be a non-empty name or removed entirely")
}

When it happens

Trigger: tools.yaml contains `bucket: ""` or an empty env-expanded value for a cloudstorage-read-object tool.

Common situations: Unset BUCKET environment variable interpolated to empty; leaving an empty quoted value instead of deleting the line; copy/paste of config skeletons.

Understand the failure class

Background: "is required", "must be set", "missing required field": configuration validation errors across open-source libraries — this error's family across 36 libraries.

Related errors

• description is required for tool %q
• bucket cannot be empty for tool %q
• description is required for tool %q
• bucket cannot be empty 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/62210abcf1795a28. Report an issue: GitHub.