Consider deprecating old routes API

**Problem**
When working with parsers, 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 locating the parser implementation and the old routes API entry points in the repository; no specific files or tests are named. Clarify which routes are deprecated and which parser errors need more detail, then define the affected behavior and add or update tests to demonstrate the completed error messages and deprecation handling.

Written by the indexing model from the issue text.