googleapis/mcp-toolbox · error

expected item at index %d to be boolean, got %T

Error message

expected item at index %d to be boolean, got %T

What it means

ConvertAnySliceToTyped converts a []any into []bool when itemType is "boolean". Each element must be exactly a Go `bool`; anything else (strings "true"/"false", numbers) triggers this error at the failing index.

Source

Thrown at internal/util/parameters/common.go:63

			tempSlice[j] = int64(i)
		}
		typedSlice = tempSlice
	case "float":
		tempSlice := make([]float64, len(s))
		for j, item := range s {
			f, ok := item.(float64)
			if !ok {
				return nil, fmt.Errorf("expected item at index %d to be float, got %T", j, item)
			}
			tempSlice[j] = f
		}
		typedSlice = tempSlice
	case "boolean":
		tempSlice := make([]bool, len(s))
		for j, item := range s {
			b, ok := item.(bool)
			if !ok {
				return nil, fmt.Errorf("expected item at index %d to be boolean, got %T", j, item)
			}
			tempSlice[j] = b
		}
		typedSlice = tempSlice
	}
	return typedSlice, nil
}

// convertParamToJSON  is a Go template helper function to convert a parameter to JSON formatted string.
func convertParamToJSON(param any) (string, error) {
	jsonData, err := json.Marshal(param)
	if err != nil {
		return "", fmt.Errorf("failed to marshal param to JSON: %w", err)
	}
	return string(jsonData), nil
}

// PopulateTemplateWithJSON populate a Go template with a custom `json` array formatter

View on GitHub (pinned to 8cc6e09de2)

Solutions

1. Have callers send native JSON booleans (true/false), not strings
2. Pre-normalize string flags to bool (parse "true"/"1" etc.) before calling
3. If string flags are unavoidable, use itemType="string" and convert downstream
4. Check the tool manifest schema to confirm the array element type is boolean

Example fix

// before
ConvertAnySliceToTyped([]any{"true"}, "boolean") // fails
// after
ConvertAnySliceToTyped([]any{true}, "boolean")

func allBools(v []any) bool {
    for _, item := range v {
        if _, ok := item.(bool); !ok {
            return false
        }
    }
    return true
}

func isBoolArray(v []any) bool {
    for _, item := range v {
        if _, ok := item.(bool); !ok {
            return false
        }
    }
    return true
}

typed, err := ConvertAnySliceToTyped(s, "boolean")
if err != nil {
    return nil, fmt.Errorf("invalid boolean array parameter: %w", err)
}

When it happens

Trigger: Passing []any{"true"} or []any{1} with itemType="boolean" — commonly from clients serializing booleans as strings or from agent-generated arguments.

Common situations: Form/query string inputs where booleans arrive as strings; YAML configs with unquoted yes/no; LLM emitting "true" instead of true.

Related errors

• expected item at index %d to be string, got %T
• expected item at index %d to be integer, got %T
• expected item at index %d to be float, got %T
• unable to bind: %w
• 'model' must be a string, got %T

AI-assisted analysis of googleapis/mcp-toolbox@8cc6e09de2 (2026-09-05). Data as JSON: /api/errors/c5af3c76782cd70b. Report an issue: GitHub.