ChessStack in 2026: The Open-Source Opening Trainer That Lets You Own Your Repertoire

Most chess players have been through the same cycle. You find an opening you like, study it for a week, then forget half the lines within a month. You know spaced repetition works. You have heard the science. But the tools that actually do it well either cost money, lock you into a platform, or give you someone else's repertoire instead of helping you build your own. ChessStack is a relatively new entry in this space, and it takes a different approach to the problem. It is an open-source, self-hostable chess opening trainer built around the FSRS spaced repetition algorithm. If that sounds niche, it is. But it solves a real problem that the bigger platforms have mostly ignored. ## What ChessStack Actually Does At its core, ChessStack is a personal opening trainer. You build your repertoire on an interactive board, and the app drills you on it using spaced repetition. That much is similar to Chessable or ChessFlare. Where it diverges is in the details. **Build mode** gives you Stockfish analysis and access to a database of 8.8 million moves from master-level games (players rated 2500+). You are not just memorizing lines someone else wrote. You are constructing your own repertoire with engine guidance and master-game statistics telling you what actually gets played at the top level. **Drill mode** uses the FSRS algorithm to schedule your reviews. More on why that matters in a moment, but the short version is this: FSRS is the same algorithm that replaced SM-2 in Anki, and it schedules reviews more accurately while requiring fewer total sessions. **Game review** lets you import your games from Lichess or Chess.com and see exactly where you deviated from your prepared lines. This is the feature that ties everything together. You study your repertoire, play games, then review where your preparation held up and where it broke down. **Puzzles** are filtered to your opening repertoire. Instead of solving random tactics, you get puzzles that come from the positions you are actually likely to reach in your games. The database includes roughly 69 MB of Lichess puzzles tagged by opening. **Gap Finder** scans your repertoire and identifies positions where you do not have a prepared response. If you have built out the Sicilian Najdorf but forgot to cover a specific move order, Gap Finder flags it. ## Why FSRS Matters If you have used Anki, Chessable, or any flashcard system in the last decade, you have probably been using SM-2, an algorithm from 1987. It works, but it treats everyone the same. FSRS (Free Spaced Repetition Scheduler) is its modern replacement, built using machine learning trained on 700 million reviews from 20,000 real users. The practical difference: FSRS learns your personal memory patterns and schedules reviews accordingly. Studies show it requires 15 to 30 percent fewer reviews to achieve the same retention rate. For chess openings, where the material is dense and the positions are similar enough to create interference, that efficiency gain is significant. Chessable still uses its own proprietary MoveTrainer system. Chessdriller and Listudy use simpler scheduling approaches. ChessStack is one of the few chess-specific tools that has actually adopted FSRS, which puts it closer to the cutting edge of memory science than most of its competitors. ## How It Compares to the Alternatives The chess opening trainer space has gotten surprisingly crowded. Here is how ChessStack stacks up against the main options. **Chessable** is the market leader. It has a massive course library, GM-authored content, and a polished mobile app. Chessable PRO runs .99/month. The tradeoff is that you are locked into Chessable's ecosystem. You buy their courses, study on their platform, and your repertoire lives on their servers. If you want to build your own lines from scratch rather than buying a course, the experience is less compelling. **Chessdriller** is free and open-source, which puts it in the same philosophical camp as ChessStack. It stores your repertoire as Lichess studies, which is clever but limiting. It lacks built-in engine analysis, game review integration, and puzzle filtering. **Listudy** is another free option that imports PGNs and Lichess studies. It is straightforward and works well for basic drilling, but it is a simpler tool without the depth of features that ChessStack offers. **ChessFlare** uses spaced repetition and has a clean interface, but it is not open-source and does not offer self-hosting. **Grind Chess** is a newer entry that also focuses on spaced repetition for openings. It is polished and user-friendly but, like ChessFlare, does not offer the data ownership that comes with self-hosting. ChessStack is not the most polished option in this list. With 4 GitHub stars and a single developer, it is clearly an early-stage project. But it is the only one that combines FSRS-based drilling, built-in engine analysis, game import with deviation tracking, repertoire-filtered puzzles, and full self-hosting capability in a single package. ## The Self-Hosting Angle This is the part that will matter to a specific type of chess player, and that type is growing. When you self-host ChessStack via Docker, your data stays on your machine. No subscription fees. No data limits. No concern about a platform shutting down or changing its terms. Your repertoire, your review history, your puzzle progress: it all lives in a PostgreSQL database that you control. For most casual players, the cloud version of ChessStack (or just using Chessable) is fine. But for serious students who have built extensive repertoires, the idea of losing that work because a platform pivots or raises prices is not hypothetical. It has happened before. Chess Position Trainer, once one of the most popular options, essentially disappeared. Users lost years of repertoire data. Self-hosting is insurance against that. And with Docker, the setup is a single command. The first boot loads the reference datasets automatically in about 30 seconds. That is a dramatically lower barrier than it would have been even a few years ago. ## Who This Is For ChessStack is not for everyone. If you want a curated library of GM courses with video explanations, Chessable is still the obvious choice. If you want the simplest possible drilling tool with no setup, Chessdriller or Listudy will do the job. ChessStack is for the player who wants to build their own repertoire from scratch, drill it with a modern algorithm, and keep everything under their control. It is for the person who imports their games after every session and wants to see exactly where their preparation broke down. It is for the developer-adjacent chess player who thinks self-hosting a training tool sounds fun rather than intimidating. The project is young. Four stars on GitHub, 146 commits, one developer (PvtTwinkle). The latest release, Data Pack v1.0, dropped in March 2026. There is a real possibility it stays small. But the foundation is solid: SvelteKit frontend, TypeScript backend, PostgreSQL database, Docker deployment, AGPL-3.0 license that guarantees the code stays open. ## The Bottom Line The chess opening trainer market is splitting into two camps. On one side, you have polished platforms like Chessable that bundle content, tools, and community into a paid subscription. On the other, you have open-source tools that give you the training mechanics without the platform lock-in. ChessStack sits firmly in the second camp, and it does it better than most. The FSRS algorithm is a genuine upgrade over what most competitors use. The game review and puzzle filtering features show a developer who actually plays chess and understands what a serious student needs. And the self-hosting option is not just a checkbox feature; it is the philosophy of the entire project. If you are the kind of player who builds their own repertoire and wants a tool that respects that investment, ChessStack is worth trying. The cloud version is free to use, and if you like it enough to self-host, the Docker setup takes about a minute. You can find ChessStack at [chessstack.app](https://chessstack.app) and the source code on [GitHub](https://github.com/PvtTwinkle/ChessStack).