> why this exists

https://docs.basedpyright.com/v1.40.2/type-server/

> The "type server protocol" is a desperate attempt from microsoft to prevent pylance from becoming obsolete by outsourcing its type checking to other language servers like basedpyright, ty or pyrefly -- while continuing to keep certain language server features exclusive to pylance.

> This protocol benefits nobody except microsoft. It adds needless complexity to any language server that chooses to support it. Basedpyright does not support it and strongly advises other language servers to avoid supporting it as well.

> For more info see here https://github.com/microsoft/pylance-release/discussions/718... and here https://github.com/astral-sh/ty/issues/1190#issuecomment-337...

It seems to be a more structured representation of the type. Normally in LSP you'd have a plain string or markdown that you render in the IDE, but nothing that you can analyse structurally.

It's a shame it's not just an LSP extension though, or a feature in a newer LSP version. LSP is maintained by Microsoft engineers.