A common proxy application is a caching Web proxy. This provides a nearby cache of Web pages and files available on remote Web servers, allowing local network clients to access them more quickly or reliably.
When it receives a request for a Web resource (specified by a URL), a caching proxy looks for the resulting URL in its local cache. If found, it returns the document immediately. Otherwise it fetches it from the remote server, returns it to the requester and saves a copy in the cache. The cache usually uses an expiry algorithm to remove documents from the cache, according to their age, size, and access history. Two simple cache algorithms are Least Recently Used (LRU) and Least Frequently Used (LFU). LRU removes the least-recently used documents, and LFU removes the least-frequently used documents.
Web proxies can also filter the content of Web pages served. Some censorware applications which attempt to block offensive Web content are implemented as Web proxies. Other web proxies reformat web pages for a specific purpose or audience; for example, Skweezer reformats web pages for cell phones and PDAs. Network operators can also deploy proxies to intercept computer viruses and other hostile content served from remote Web pages.