The Tetris Guideline is the current specification that The Tetris Company enforces for making all new (2001 and later) Tetris game products alike in form. A mode labeled "standard" or just plain "Tetris" will adhere to the Guideline more closely than other modes.
In 2011 a copy of the Tetris Guideline was leaked, dating to 2009. It is likely that the Guideline has been modified since that time, but most of the rules specified there are still followed by current versions.
As of 2018, the Guideline is conjectured to encompass the following rules, learned through the observation of the behavior of authentic Tetris games:
- Playfield is 10 cells wide and 20 cells tall, with a 20 cell buffer zone above the top of the playfield, usually hidden or obstructed by the field frame.
- Tetromino colors
- Cyan I
- Yellow O
- Purple T
- Green S
- Red Z
- Blue J
- Orange L
- Tetromino start locations
- The I and O spawn in the middle columns
- The rest spawn in the left-middle columns
- The tetrominoes spawn horizontally and with their flat side pointed down, and move down immediately after spawning.
- Super Rotation System (SRS) specifies tetromino rotation and wallkicks. There may be an option to disable wallkicks.
- Standard mappings for console and handheld gamepads:
- Standard mappings different from console/handheld gamepads for computer keyboards
- Standard mappings for mobile keypads
- Standard mappings for remote controls
- So-called Random Generator (also called "random bag" or "7 system")
- Hold piece: The player can press a button to send the falling tetromino to the hold box, and any tetromino that had been in the hold box moves to the top of the screen and begins falling. Hold cannot be used again until after the piece locks down. Games on platforms with fewer than eight usable buttons (such as the version on iPod) may skip this feature. The combination of hold piece and Random Generator would appear to allow the player to play forever.
- Game must have ghost piece function.
- Terms used in the user manual: "Tetriminos" not "tetrominoes" or "tetrads" or "pieces", letter names not "square" or "stick", etc.
- Marathon speed curve is based on that used in Tetris Worlds.
- Designated soft drop speed. Details vary between guideline versions.
- 0.5 second lock delay when gravity is less than 20G.
- Move reset with a limit of 15 lock delay resets from rotations or left/right movements ("Extended Placement"). There may be an option to disable this behaviour and use step reset instead, or remove the limit of resets.
- Player may only level up by clearing lines. Required lines depends on the game.
- The game must use a variant of Roger Dean's Tetris logo, although this was true from around 2000 - before the guidelines emerged. The guideline contains rules for the use of the logo and what modifications are acceptable.
- Game must include a version of Korobeiniki. Note that The Tetris Company holds a sound trademark on the variation of the song used in Tetris games.
- The player tops out when a piece is spawned overlapping at least one block, a piece locks completely above the visible portion of the playfield, or a block is pushed above the 20-row buffer zone.
- Scoring#Recent_guideline_compatible_games system, including Back-to-Back recognition rules
- Combo recognition
- Line attack garbage system in multiplayer
- T-Spin rules based on the 3-corner method, and T-Spin Mini rules based on the pointing side cell method.
- At least one piece preview by default.
Recommended but non-mandatory
- Display of multiple next-coming tetrominoes. Most games show at least three, though there are no hard rules. A maximum of six is recommended.
- DAS no faster than Tetris Zone.  (However, some Japanese games blend the Guideline with the Sega tradition of 1G DAS: Tetris New Century, Kiwamemichi, and the TGM collection.)
- Marathon, Sprint and Ultra modes. In general Sprint and Ultra will only be omitted for hardware reasons.
- Game title should begin with "Tetris".
Although Guideline-compliant games share many traits, they also have differences in many aspects as well. There are a few instances where a game will break a trait which is shared by all other games thought to be compliant. Examples of this include the lack of the hold function and the T-spin's ability to start and continue Back-to-Back chains in iPod Tetris, and the inverted rotation button layout of TGM3 and TGM ACE (or Kiwamemichi, depending on interpretation). No explanations have been given for the reasons of these games' deviations.
Henk Rogers has been quoted as revising the guideline annually. Known versions of the guideline include 2002, 2005, 2006 and 2009, and guideline 2002 games have been built from scratch and released as late as 2005.
So far, the first confirmed guideline 2005 games (TGM ACE) has been released in December 2005, while the first confirmed guideline 2006 game (Tetris: New Century, although iPod Tetris released earlier behaves similarly) was released in September 2006. Therefore, it can be conjectured that the schedule of a new guideline version is released somewhere between the middle to the latter half of the year. Mihara's blog has mentioned discussions on revising the guideline in 2008 and 2010. The leaked guideline is dated March 2009.
While many games have no publicly visible indication of the guideline version by the developer or publisher, some games have had their exact guideline versions made clear by them. They are listed in the Guideline compliant game differences page.
Known or suspected modifications
- Buffer zone size (in 2002 versions, at least 2 rows)
- T-Spin and T-Spin Mini recognition rules
- 2005: 3-corner T
- 2006: 3-corner T no kick
- Lock delay: the 15 reset limit was specified by 2009 and present in Tetris Zone (2007), while earlier games are known to use unlimited resets instead.
- Rewarding of Back-to-Back chains. Recognition method depends in the game.
- Soft drop speed; Tetris Zone uses 20 times the current level's fall speed, while other games have different speeds.
- Scoring and combos were fixed some time after 2006.
- Guideline compliant game differences
- Tetris Worlds, Tetris Deluxe, and Tetris Zone, considered by many to be the "reference" implementations of the Guideline at the respective times of the games' releases.
- Tetris DS, another popular game that is compliant with the Guideline