The directory is a big list of hackerspaces URLs that provide information like contact information, the door status or even sensor data such as the temperature or the amount of computers that have currently leased an IP. In the following a hackerspace URL is simply called endpoint.
If you are a developer who wants to write an application based on the Space API, you can fetch the directory directly from this website.
Some Space API versions are not downwards compatible. If you need endpoints that have a specific version implemented you can filter those out with the following URL.
There's more. If you write an application which is only interested in endpoints that provide webcam streams you should use the filter option.
There's more to discover. Learn more about the filters.