googleapis/mcp-toolbox · error

bucket %q is not allowed by source %q configuration

Error message

bucket %q is not allowed by source %q configuration

What it means

CloudStorage source implements an allowlist: if 'allowedBuckets' is configured, every bucket-touching operation (list, read, create, metadata, IAM policy) is checked against it. A request for a bucket not on the list is rejected before any GCS API call. If the list is empty, all buckets are permitted.

Source

Thrown at internal/sources/cloudstorage/cloudstorage.go:104

}

var _ sources.Source = &Source{}

type Source struct {
	Config
	client *storage.Client
}

func (s *Source) validateBucket(bucket string) error {
	if len(s.AllowedBuckets) == 0 {
		return nil
	}
	for _, b := range s.AllowedBuckets {
		if b == bucket {
			return nil
		}
	}
	return fmt.Errorf("bucket %q is not allowed by source %q configuration", bucket, s.Name)
}

// validateLocalPath enforces allowedLocalRoots. The path must sit under an
// allowed root both as written and after symlinks are resolved: the first check
// keeps the rejection message tied to what the caller actually asked for, and
// the second is what makes the root a real boundary, since a symlink planted
// under a root can otherwise point anywhere on the filesystem.
//
// The resolved comparison uses resolved roots as well, so an allowed root that
// is itself reached through a symlink (/tmp on macOS, a symlinked workspace)
// still matches.
func (s *Source) validateLocalPath(p string) error {
	clean, err := cloudstoragecommon.ValidateLocalPath(p)
	if err != nil {
		return err
	}
	if len(s.AllowedLocalRoots) == 0 {
		return nil

View on GitHub (pinned to 8cc6e09de2)

Solutions

1. Add the requested bucket name (exact spelling) to 'allowedBuckets' in the cloud-storage source config and restart the toolbox.
2. Check for case/typo mismatch between the requested name and the allowlist entry.
3. If all buckets should be accessible, remove the allowedBuckets field (empty list permits everything).

Example fix

# before
allowedBuckets: [my-bucket-a]
# after
allowedBuckets: [my-bucket-a, my-bucket-b]

allowed := map[string]bool{"my-bucket-a": true, "my-bucket-b": true}
if !allowed[bucketName] {
    return fmt.Errorf("bucket %q must be added to allowedBuckets", bucketName)
}

When it happens

Trigger: Calling ListObjects, ReadObject, CreateBucket, GetBucketMetadata, GetBucketIAMPolicy, or GetObjectMetadata with a bucket name that is not an exact (case-sensitive) entry in the source's allowedBuckets list while that list is non-empty.

Common situations: LLM agent requests a bucket that exists in GCP but was never allowlisted in the toolbox config; typos or case mismatch between config and actual bucket name; buckets added in GCP after the config was written.

Related errors

• local path %q is not under any allowed local roots for sourc
• description is required 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

AI-assisted analysis of googleapis/mcp-toolbox@8cc6e09de2 (2026-09-05). Data as JSON: /api/errors/bb10b41b9b0aaaf9. Report an issue: GitHub.