Refactor data for better readability

**Problem**
When working with validation, 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 file, test, or entry point is named. Start by locating the validation and error-handling paths, then review the current messages and existing tests; the work is done when the affected validation errors are more descriptive and the relevant behavior is covered by tests.

Written by the indexing model from the issue text.