How to Prepare Against an Online Chess Opponent
If your next opponent plays on Chess.com or Lichess, you're in luck. Their whole rated history is public, tied to a username, and easy to analyze. No database subscriptions, no digging through old games. Fair warning that I'm biased here: half the reason Chess Stalker exists is a guy at my university club who beat me with the same anti-Sicilian for an entire semester. Once I finally sat down with a few hundred of his games instead of skimming the last five, the fix took one evening. This guide shows how I turn a username into a game plan. Everything below is free and works without an account.
For the screenshots I'll use a player you probably know: Hikaru's Chess.com profile. Every panel you see here is from his real report.
Type the username
Open Chess Stalker, pick Chess.com or Lichess, type the username and hit Analyze. The report takes a few seconds: the site pulls their rated games through the platforms' public APIs and runs everything in one pass.
This is the part that fixes the mistake I was making against my club rival: reviewing a handful of recent games by hand and calling it prep. Real patterns only show up in bulk: fifty games sketch a player, a few hundred make the numbers honest. Hikaru's report covers 2,847 games from the last six months.
Once the report is open, use the Filters button in the top bar to match the game you're preparing for: pick the time controls, rated or casual, and the period. The whole report recalculates when you apply them.
Start with How to Beat
The How to Beat card is where the preparation actually happens. It splits their repertoire into weaknesses (lines they keep losing) and strengths (lines you should stay out of). There's a toggle for the color you'll have against them, and clicking any line opens it on a board where you can surf through the moves one by one, with their stats at every step. That viewer is worth slowing down for: it's the fastest way to learn a line you've never played.
Two things to look for here. First, the line they keep losing: if they've walked into the same bad variation for months, odds are they'll walk into it against you too. Second, the sample size. When a line says "7 games, low sample", don't build your whole prep on it. But a low sample also tells you something: nobody is booked up everywhere, and a line they rarely face is a line they rehearsed less.
Then cross-reference with your own repertoire. The winning move is the intersection, a line where their numbers are worst and you feel at home. One well chosen line per color beats ten notes you won't remember at the board.
Check how exploitable they are
The Stalker Score compresses the whole analysis into one number from 0 to 100: how exploitable this player is. It's built from four signals measured across every game, and each one is a different way people crack: they melt in time trouble, they tilt after losses, they play the same three openings, or they repeat the same patterns.
Hikaru scores 27, a hard target, which is what you'd expect from a super GM. Normal people score much higher (the semester guy from my club sits in the 60s, which was comforting to see). Whatever the highest bar is, that's the door to knock on: here the strongest signal is repetitive patterns at 35, so the openings work from step 2 matters more than the clock.
Rehearse against their Twin Bot
Knowing the line and remembering it at the board with a clock running are two different skills. Chess Stalker builds a Twin Bot from the analyzed games, a bot that plays your opponent's real openings and tendencies instead of perfect engine moves. Use it to rehearse the line you picked in step 2 until steering the game there feels automatic.
Read their psychology
The Psychology card measures mental resilience across six signals: stability, tilt, post-loss recovery, timeouts, losing streaks and how they handle lost positions. This is the part a game-by-game review never shows you, because each number needs hundreds of games to mean anything.
How to use it: a high tilt number means the games right after you beat them are the best time to queue again. A low post-loss recovery means one win against them is often worth two. Hikaru recovers 73% of the time and tilts almost never, so no free points there; plenty of players are the opposite.
Read their clock personality
The Player Card shows their rating in every time control side by side, and the Time management card shows where their clock actually goes: when they leave book, how often they end up in time trouble, and what it does to their play.
A player much stronger in blitz than rapid lives on instinct, so deny them familiar forcing lines and make them calculate. A player who drifts into time trouble can be pushed there on purpose with sharp structures early. Hikaru's report flags that his blunder rate triples below 30 seconds and that time trouble tends to start around move 27. Not that I'd try to flag Hikaru, but when an 1800 shows the same pattern, dragging the game into a sharp middlegame with the clock ticking is a legitimate plan on its own.
Check the traps, both directions
The Traps cards work both ways. Traps Used shows the tricks they like to spring, so you don't walk into them. Falls Into shows the traps that have caught them before, and a trap that worked once tends to work again, especially in fast time controls.
Walk their repertoire tree
When you want to go past the shortlist, the Repertoire section is the full map: an explorable tree of every move they play as White and as Black, with games, performance and win rate at each branch, next to a board that draws their most played moves as arrows. Every board in Chess Stalker comes with Stockfish 18 built in, so you get engine evaluations on any position while you browse. This is where you check how deep a habit goes and where exactly the numbers turn bad.
Note the "1428 Games" bar: that's his whole record as White in one glance, and it updates as you click deeper into a line. The Strong and Weak tags do the reading for you, and the arrows on the board show what you'll most likely face. More than two thirds of hikaru's White games start 1.e4 or 1.b3, both near 80% or better.
Go deeper if you need to
Everything above is free. If you want the really detailed stuff, PRO adds the head-to-head view with your full record against every rival you've faced and the openings behind it, the frequent rivals list with easy targets flagged, and win rates across all 14 endgame types with every game linked. If you play the same people every week, in your club or online, that history is its own dataset and worth mining. For a casual prep session you won't need it.
One last pointer: if the rival you're preparing for also plays rated tournaments over the board, their FIDE games are scoutable too, from just their name. That side of the method has its own walkthrough in the FIDE preparation guide.
Frequently asked questions
Is scouting an online opponent allowed?
Yes. Rated games on Chess.com and Lichess are public by design and served through official APIs. Studying them beforehand is normal preparation. What's forbidden is getting help during the game.
Do I need my opponent's permission or account access?
No, just their username. Everything runs on their public rated games, the same ones anyone can replay from their profile.
How long does the analysis take?
Seconds for most accounts. The report loads in one pass and you can start reading while the deeper stats finish.
What if they have only played a few games?
Under 50 rated games or so, the win rates per line aren't trustworthy yet. The report marks these as low sample. Read them as tendencies, not facts, and lean more on general preparation.
Does it work the same on Chess.com and Lichess?
Yes. Both expose full rated histories, so the method is identical. If your opponent is active on both, scout both accounts. Repertoires sometimes differ between platforms.