Swapnote (called Nintendo Letter Box in Europe and Australia) is a free, downloadable messaging service application for the Nintendo 3DS released on December 22, 2011. It allows users to write notes (up to four pages) using the stylus and send them via StreetPass and formerly SpotPass, the latter only allowing users to send to notes to people in their Friend List. Users can reply to each note once, and replies are restricted to one page. Swapnote's mascot is a Mii named Nikki, who automatically sends notes to users as they continue to use Swapnote.
While sending a note to their friend, a user gains access to a variety of features, including the ability to attach photos stored in an SD Card, to create messages and art displayed in full 3D, to change the stationery on which notes are written, to view notes in a slide show format, and (using 15 Play Coins) to attach sound recordings from the Nintendo 3DS Sound application. Swapnote can store a combined maximum of 3,000 notes and replies, and each note can have a maximum of 100 replies attached to it, with new notes/replies replacing old ones once the limit has been reached. Notes given "Favorite" status are not deleted, though replies are.
On November 17, 2016, Swapnote received a sequel titled Swapdoodle, which retains similar elements (except photo and sound attachments) with new features. There are now Doodle Lessons for players where they can practice drawing, along with stamps and secret pages. The application is free-to-start, but consists of in-game purchases.
An update for Swapnote was released on July 5, 2012 in Japan, Europe, and Oceania which adds the feature to change the ink's colors by pressing either left or right on the , with North America receiving the feature shortly afterward. An April 2013 update allows users to use different colors of ink on each page in one note and added some more features to the software, such as the ability to delete multiple notes at once.
On October 31, 2013, Nintendo suspended the SpotPass functionality of Swapnote in all regions, due to various incidents where the app was used to share explicit content with minors. This not only affected interaction between users but also halted the reception of special notes and stationery from developers.