Restricting access to network resources through recursive URL classification

In one example, a server-based system may provide a recursive classification of the contents of a URL by: 1) receiving a request for a URL-classification list associated with a base URL, 2) constructing the URL-classification list, and 3) providing, in response to the request, the URL-classification list. The resulting URL-classification list may comprise: 1) content categories occurring in the base URL and 2) content categories occurring in any URLs embedded in the base URL. In another example, a client-based system may restrict access to network resources, based on the contents of a base URL, by: 1) identifying a request from a user to access a base URL, 2) requesting a URL-classification list associated with the base URL, 3) receiving the URL-classification list, and 4) determining, based on the URL-classification list, that access to the base URL is authorized. Corresponding computer-readable media are also disclosed.