A shoutbox, saybox, tagboard, chatterbox or chat box is a chat-like feature of some websites that allows people to quickly leave messages on the website, generally without any form of user registration.
In their simplest form, shoutboxes are simply lists of short messages, possibly with information about their authors. The page may be automatically refreshed after a certain interval, or polled dynamically in order to keep new messages visible. Older posts are often deleted after a certain number of messages have been written in order to preserve space on the server.
Like most dynamic content, shoutboxes typically interface with a database, and some may query the database every time a page is requested. Unlike most dynamic content, however, shoutboxes are generally placed on every page of a web site, so they tend to cause disproportionate strain on databases. Therefore, care must be taken to ensure that shoutboxes do not use too many database resources. Caching systems like memcached can be used to mitigate this to some extent, or an alternative implementation such as storing all messages in system-wide shared memory rather than a database may be used. Alternatively, a shoutbox may be loaded from a flat file.