Custom tool to extract xml

[Parseval123]

Hello everyone,

I'm developing a custom tool for my agent, which is essentially a Python method that extracts very specific fields from an XML file.

The XML files I handle are very long, and I've noticed that when the agent tries to pass the content, it 'resolves' the XML tags, resulting in incorrect content being passed to the method. I've tried to strengthen the system instruction, but it seems there's no way to bypass this behavior in Gemini (both Pro and Flash).

Do you know why this happens? Is it conceptually wrong to build tools based on programmatic and deterministic tasks, such as executing a Python function?

Thank you in advance.
P.