expected allowedDataset to have at least 2 parts (project.da

Error message

expected allowedDataset to have at least 2 parts (project.dataset): %s

What it means

buildParams for bigquery-execute-sql parses each entry in allowedDatasets, which must be a fully-qualified BigQuery dataset of the form project.dataset. When a single allowed dataset has no dot (fewer than 2 parts), the tool cannot construct the SQL-guard description and returns this error at Initialize/resolveParams time.

Source

Thrown at internal/tools/bigquery/bigqueryexecutesql/bigqueryexecutesql.go:279

// buildParams builds the tool's parameters from the source's write mode and allowed-dataset
// configuration. Empty writeMode and a nil allow-list yield the plain skeleton.
func buildParams(writeMode string, allowedDatasets []string) (parameters.Parameters, error) {
	var sqlDescriptionBuilder strings.Builder
	switch writeMode {
	case bigqueryds.WriteModeBlocked:
		sqlDescriptionBuilder.WriteString("The SQL to execute. In 'blocked' mode, only SELECT statements are allowed; other statement types will fail.")
	case bigqueryds.WriteModeProtected:
		sqlDescriptionBuilder.WriteString("The SQL to execute. Only SELECT statements and writes to the session's temporary dataset are allowed (e.g., `CREATE TEMP TABLE ...`).")
	default: // WriteModeAllowed
		sqlDescriptionBuilder.WriteString("The SQL to execute.")
	}

	if len(allowedDatasets) > 0 {
		if len(allowedDatasets) == 1 {
			datasetFQN := allowedDatasets[0]
			parts := strings.Split(datasetFQN, ".")
			if len(parts) < 2 {
				return nil, fmt.Errorf("expected allowedDataset to have at least 2 parts (project.dataset): %s", datasetFQN)
			}
			datasetID := parts[1]
			fmt.Fprintf(&sqlDescriptionBuilder, " The query must only access the `%s` dataset. "+
				"To query a table within this dataset (e.g., `my_table`), "+
				"qualify it with the dataset id (e.g., `%s.my_table`).", datasetFQN, datasetID)
		} else {
			datasetIDs := []string{}
			for _, ds := range allowedDatasets {
				datasetIDs = append(datasetIDs, fmt.Sprintf("`%s`", ds))
			}
			fmt.Fprintf(&sqlDescriptionBuilder, " The query must only access datasets from the following list: %s.", strings.Join(datasetIDs, ", "))
		}
	}

	sqlParameter := parameters.NewStringParameter("sql", sqlDescriptionBuilder.String())
	dryRunParameter := parameters.NewBooleanParameter(
		"dry_run",
		"If set to true, the query will be validated and information about the execution will be returned "+

View on GitHub (pinned to 8cc6e09de2)

Solutions

Change the allowedDatasets entry to the fully-qualified form 'project.dataset' (e.g. my-project.my_dataset).
Check for typos such as missing dots, extra dots, or trailing whitespace in the config value.
If using multiple datasets, ensure every list element independently satisfies project.dataset format.
Re-run initialization; the error names the offending value to fix.

Example fix

// before (tools.yaml)
allowedDatasets:
  - my_dataset
// after
allowedDatasets:
  - my-project.my_dataset

Defensive patterns

Strategy: validation

Validate before calling

for _, d := range cfg.AllowedDatasets {
    if len(strings.Split(d, ".")) < 2 {
        return fmt.Errorf("allowedDataset %q must be project.dataset", d)
    }
}
// then Initialize

Try / catch

if _, err := cfg.Initialize(ctx); err != nil {
    if strings.Contains(err.Error(), "at least 2 parts") {
        // fix allowedDatasets entries to project.dataset and re-init
    }
    return err
}

Prevention

Always write allowed datasets as fully-qualified project.dataset strings.
Add config validation for allowedDatasets format before Initialize.
Beware of trailing dots, spaces, or comma-joined values in YAML list entries.
Document the project.dataset requirement in your config templates.

When it happens

Trigger: Configuring allowedDatasets with a bare dataset id like 'my_dataset' (or a value with only whitespace/malformed qualifiers) instead of 'my-project.my_dataset', then initializing the tool.

Common situations: Copy-pasting a dataset id from the BigQuery console without the project prefix; assuming the source's default project is applied automatically; typos like a trailing dot or comma-separated values in one list element.

Related errors

AI-assisted analysis of googleapis/mcp-toolbox@8cc6e09de2 (2026-09-05). Data as JSON: /api/errors/6f4967a9b13f1010. Report an issue: GitHub.