Abstract: A link-modifying web server automatically modifies links in each web page as it is served to a client browser. The web page is parsed for links, and the links are looked up in a link mapping database. A replacement field is read from the database. A link modifier alters the link using the replacement field to point to a different server at one of several content delivery providers. One of several replacement links can be selected from the link mapping database depending on network conditions and user account data. A replacement link to one content delivery provider can be chosen rather than another replacement link to a different content delivery provider when one provider's network is responding more quickly or has a lower cost. A provider monitor continuously checks provider performance at each of the content delivery providers. When one provider's network is slow or fails, the provider monitor instructs a delivery rule processor to choose link replacements at other content delivery providers.