The Tetris guideline is the current specification that The Tetris Company enforces for making all new (2001 and later) Tetris games alike in form. The company revises the guideline annually. A mode labeled "standard" or just plain "Tetris" will adhere to the Guideline more closely than other modes.
As of 2006, the Guideline is conjectured to encompass the following rules, learned through observation of the behavior of authentic Tetris games:
- Playfield is 10 cells wide and at least 22 cells tall, where the top two are hidden or obstructed by the field frame
- Tetromino colors
- Cyan I
- Yellow O
- Purple T
- Green S
- Red Z
- Blue J
- Orange L
- Six next-coming tetrominoes visible or at least three.
- So-called Random Generator (also called "random bag" or "7 system")
- Tetromino spawn 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.
- Standard mappings for console and handheld gamepads:
- Super Rotation System (SRS) specifies tetromino rotation
- Infinity based lockdown behavior
- "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.
- Terms used in the user manual: "Tetriminos" not "tetrominoes" or "tetrads" or "pieces", letter names not "square" or "stick", etc.
- Player may only level up by clearing lines.
- Game must include at least one of the songs Korobeiniki, Katjusha, or Kalinka.
The combination of hold piece and Random Generator would appear to allow the player to play forever.
The extent to which the Guideline specifies the speed curve, the scoring system, and other aspects not listed on this page, is not yet known to the public.
Although Guideline-compliant games share many traits, they also have differences in many aspects as well.
- Tetris Worlds and Tetris Deluxe, considered by many to be the "reference" implementations of the Guideline
- Tetris DS, another popular game that is compliant with the Guideline