Does one exact release work with another exact release, and on what evidence? Call this once both sides are pinned: a PyPI or npm package release, or a Python or Node runtime release. Do not call it with a version range or file contents; resolving ranges and reading a codebase are out of scope. Argument order is meaning. Under the pypi -> pypi requires_dist and npm -> npm dependencies rules, order fixes the declaring side, so swapping arguments asks a different question. For pypi with runtime:python and npm with runtime:node the declaring side follows from the kind of target, so either order reads the same; relation.direction reports which way the server read it. A verdict of unknown is a normal result meaning the claim cannot be proven from current evidence. It is not an error and not a reason to retry: limitations and sources_checked carry the next thing to check.

What does one exact release declare and state about compatibility, so you can compare it with code you already hold? Call this when a single target is pinned and you want its declared constraints and reviewed changes. Do not call it with a version range, a repository path, or source text; the server is never given a codebase and compares nothing for you. This tool takes one target, so it has no argument order to get wrong; ordering matters only in check_compatibility, where input order fixes the declaring side for the pypi -> pypi and npm -> npm rules while the kind of target fixes it for the runtime rules, and relation.direction reports how the pair was read. An availability of unknown is a normal result meaning current evidence proves nothing here, not an error and not a reason to retry: limitations and sources_checked carry the next thing to check.