BSK-E0013 error

Return type mismatch — inferred return type incompatible with annotation

When a function has a return type annotation, the inferred return type must be assignable to the declared type. This extends the original -> None check to handle all return type mismatches using the inference system.

Real basilisk check output

What you see when BSK-E0013 fires on a minimal example:

basilisk check output reporting BSK-E0013 — Return type mismatch — inferred return type incompatible with annotation

How to handle it

Every rule is on by default — strict is the default, not a cage. You can dial BSK-E0013 down per-file or per-path from your editor or pyproject.toml, or fix the code so it type-checks. See the Type Safety rules and the complete diagnostic reference.

Canonical URL: https://www.basilisk-python.dev/errors/BSK-E0013