Project Slippi is an ongoing project that aims to give Super Smash Bros. Melee several major quality of life features originally not present in the game. As of June 2020, the features currently included are automatically saved replays, live match mirroring, rollback netcode, and integrated online matchmaking. The project was created and is being led by Fizzi with major contributions from UnclePunch, Nikki, and metaconstruct.
A number of unofficial Slippi-compatible projects have been created by the community for various purposes.
The project was publicly launched on June 18th, 2018, but had been in a "private beta" since February of that year. The initial release featured automatically saved replays and detailed match statistics. Prior to this launch, the statistics system was previously used at HTC Throwdown, Smash Summit 7, and Smash Rivalries for use on stream. On September 29th, 2018, Smashladder announced that Project Slippi had become the community's main Dolphin build.
On January 13th, 2019, a stream would be held announcing a feature that enabled live mirroring from console to Dolphin. This would allow for high quality streaming of the game with no additional hardware required. This feature was in "beta" and accessible to Patreon supporters until March 10th when it was released to the public. On February 22nd, Phoenix Blue 2 would become the first tournament to use Project Slippi for high quality streaming of the event. On March 9th, The Gang Steals The Script would become the first North American tournament to use Project Slippi. Every tournament setup featured the ability to automatically save replays and the stream also utilized Slippi for data analysis and high quality streaming. On the same day, slippi.gg would be launched. This website includes downloads of the project as well as nearly every replay from The Gang Steals The Script. From this point forward, every future major tournament utilizing Slippi would now appear on the website. On April 20th, 2019, a feature would be added to the website that would allow users to preview games via a lightweight in-browser visualizer designed by Will Blackett. On November 27th, Fizzi would announce that he would begin working on Slippi full-time.
On June 22nd, 2020, an update was released for the custom Slippi Dolphin build that would introduce rollback netcode and integrated matchmaking into the game. This became a major breakthrough in the competitive Super Smash Bros. Melee community as distance-based latency would no longer be an issue. Due to the COVID-19 pandemic, most in-person tournament activity had been completely shut down since March 2020, and Project Slippi became the dominant method of playing Melee, with major tournament organizers hosting events using the new updates. Project Slippi has since been credited with bringing new players into the competitive Melee scene, due to its ease of access and ability to provide practice against anyone online.
On January 19th, 2021, v2.2.4 was released, introducing a hidden match-making rating (MMR) into random unrated matches. The update restricted the search range for players with low MMR dramatically while maintaining a wide search range for players of average skill or better. This was aimed at creating more balanced matchups at lower levels of play, preventing newer players from receiving crushing defeats against more experienced players, and increasing new player retention levels.