1. A method comprising: receiving at a proxy a request from a client; wherein the request comprises a search query submitted by a user; the proxy performing a modification to the request to generate a modified request, wherein the modification includes adding to the request a proxy identifier that uniquely identifies the proxy, wherein the modification is performed by the proxy without regard to the content of the request from the client; the proxy forwarding the modified request to a search engine, wherein the proxy identifier in the modified request indicates to the search engine a particular proxy-specific customization to apply to a search engine results page to generate a customized search engine results page, wherein the particular proxy-specific customization is one of a plurality of proxy-specific customizations, wherein each of the plurality of proxy-specific customizations is mapped to a corresponding proxy identifier; receiving at the proxy, from the search engine, the customized search engine results page having (a) search result items that match the search query and (b) the particular proxy-specific customization, wherein the particular proxy-specific customization includes at least one of: proxy-specific information; or placeholders for proxy-specific information; and wherein the method is performed by one or more computing devices.