Keystone55 is an open web gazetteer — a structured register of online addresses organised into 22 named districts. The catalogue currently holds 832 entries, each reviewed and placed in the sector that best represents its primary function, from financial services and healthcare to travel operators and technology firms. The gazetteer follows the tradition of printed reference works that map a territory by listing its notable addresses, recording what is there and where it belongs. In Keystone55's case, the territory is the open web, and the districts are defined by subject and trade rather than geography. Each entry in the register includes the site's address, a brief description, and its assigned district. Sites span a wide range of national markets and languages, reflecting the international character of online activity. The register is maintained as an ongoing project. New entries are added as submissions are reviewed; the catalogue is not static. The aim is to keep the record current and useful as an open reference resource. Keystone55 is free to consult and free to join. If you maintain a website and would like it included in the register, you can submit it using the form on the Add a Site page. The curator reviews each submission before assigning it to the appropriate district.