# Specification


The specification is the source of truth for Xo. These pages are generated
from `spec/core.md` and `spec/std.md` in the repository, so they always match
the released toolchain's draft.

- [Core language](core/): syntax, types, errors, concurrency, effects, modules,
  and the diagnostic codes.
- [Standard library](std/): prelude methods and the `std` packages.