Refactor core for better readability

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

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

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

Start by inspecting the error-handling code under lib and identify which messages are currently too vague. The issue is complete when error messages provide more useful debugging context without changing the intended behavior.

Written by the indexing model from the issue text.