Add TypeScript types for utils

**Problem**
When working with api, the error messages could be more descriptive.

**Suggestion**
Improve error handling and add detailed error messages.

**Context**
This would help with debugging and maintenance.

No files, tests, or entry points are named. Start by reconciling the title's TypeScript types request with the body’s broader error-handling suggestion and locate the relevant API utilities; done should mean the intended utility types and more descriptive API errors are implemented, with verification defined.

Written by the indexing model from the issue text.