PLAY WITH INTENT.

A little more practice.
A little less guesswork.

Stacking Lab is a free, ad-free Tetris practice tool that runs in your browser. Choose a skill, inspect suggested placements or watch its coach play from your board, then try the decisions yourself.

What can I practise?

Each mode has its own coach and objective. Pick the pattern you want to work on instead of expecting one strategy to cover every situation.

Stacking: 9–0 and 6–3 stacking, LST and ST stacking, DT, TST, TS, STSD and Fractal. Work on a cleaner stack, T-spin structures and the transitions between building and clearing.
4-Wide combos: Build the six left columns and leave a four-column channel on the right. The coach builds toward the height guide, then tries to keep consecutive line clears going.
Openers: Practise opening sequences with step-by-step placement suggestions. Examples include TKI, DT Cannon, MS2, Gamushiro and New DT Cannon. Some openers have alternative solutions for piece orders that cannot use their default setup.
Downstacking: Practise clearing garbage and finding a route down the field. The mode includes garbage pressure with an adjustable arrival interval.
Perfect Clear: Freeplay with a dedicated coach that tries to clear every block from the board. A Perfect Clear leaves the board empty; clearing a line while blocks remain does not count.

Start with one thing to practise

Open the trainer and choose a mode. Start with 9–0 for a simple stacking goal, or choose the specific pattern you want to study.
Give yourself time. Turn gravity off to think through each placement. You can adjust the visible NEXT queue and your controls in the app.
Compare your idea with the suggestion. Inspect the suggested sequence or use Auto Play to watch the coach demonstrate its approach.
Review, then try again. Use Undo and game history to revisit a decision. Coach-played moves are excluded from your placement success rate.

How does the coach choose moves?

The coach searches legal placements using the visible piece queue and available Hold. It scores the resulting positions against the selected mode’s rules and goals. Each mode owns an independent coach, so a 4-Wide coach aims for combos while a Perfect Clear coach aims to empty the board.

The coach does not always choose the strongest competitive move. It prioritizes the skill being practised and searches within a time budget. Suggestions can be imperfect, difficult boards may need recovery, and a coach can stop when it cannot verify a reliable continuation.

This is a local game-search system, not a chat model or a remote AI service. The game and coach calculations run on your device, with coaching work in browser Web Workers.

A few useful answers

Is Stacking Lab free?

Yes. The trainer is free and ad-free, and you do not need an account to practise. Optional support helps cover hosting costs.

What do I need to play?

A modern browser with JavaScript enabled and a keyboard. The trainer offers configurable controls and TETR.IO, approximate Tetris 99 and custom handling profiles. It is not a perfect reproduction of those games.

Does the coach see pieces I cannot see?

It uses the visible NEXT queue and Hold. It can account for the observed seven-bag, but does not read the exact hidden queue to invent a known continuation.

Where are my games and settings stored?

On the live website, settings and game history are stored in your browser. They do not automatically sync across devices. You can export a game as JSON from history. Clearing browser data can remove local records.

What happens when I send feedback?

The feedback form sends your message, category, optional contact details and the current mode and game ID to the server. Feedback is stored separately from browser game history.

Is the source code public?

The repository is private. Like other browser applications, the JavaScript delivered to your browser can be downloaded and inspected. This does not make the project open source.

Who made it?

The Last Vogon, a Tetris fan who started building a practice tool for personal use and decided to share it. Stacking Lab is an independent fan-made project, not an official Tetris product.

Can I suggest a feature?

Yes. Open the trainer and choose Feedback in the footer to send an idea or report a problem.