But how closely do today's type checkers actually follow the Python typing specification? In this post, we look at what typing spec conformance means, how different type checkers compare, and what the conformance numbers don't tell you. This created a problem: the semantics of the type system were scattered across many documents, and different type checkers implemented slightly different interpretations. To address this, the typing community began consolidating the rules into a single reference: the Python typing specification. The spec describes the semantics of typing features and includes a conformance test suite that type checkers can run to measure how closely they follow the spec.