You don't need an opening repertoire yet. Here's why.

The short answer

If you're under about 1400, you do not need an opening repertoire. You need a set of rules you can apply to any position on move 6, because your opponent will have left any book line by then and so will you.

This isn't the usual "principles over memorisation" sermon. It's an argument about where the damage in your games actually happens, and the damage is measurable. The opening is not where you lose. It's just the part of the game you can study from a video while doing something else, which is why it feels like the obvious place to start.

Where your games are actually decided

Across 185,694 engine-classified moves in 5,923 games analysed on Mated, 3.8% of moves played are outright blunders and another 4.2% are mistakes. That's roughly one move in twelve that's a real error, before you count the 18.5% classed as inaccuracies. Nobody gets to move 12 of an Italian and then plays 30 clean moves.

The same set of games shows where those errors sit. In the middlegame, 9.1% of moves are a mistake or worse. In the endgame, it's 2.3%. That's a four-fold difference in error rate between two phases of the same games.

One caveat, because the number is easy to over-read: endgames look clean partly because there are fewer legal ways to go wrong with six pieces on the board, and partly because games that reach an endgame are by definition games where nobody hung a rook on move 22. The 2.3% is not proof that endgames are easy. It's proof that the middlegame is where the pile-up is.

There's a third number worth sitting with. The average move in that dataset gives away 95 centipawns against the engine's best, but the median is far lower — a small number of very bad moves carry most of the damage. Your rating is not the sum of a thousand small imprecisions. It's a handful of catastrophes per game, surrounded by moves that are broadly fine.

A repertoire does nothing about any of this. It changes which position you arrive at on move 10. It does not change what you do when your opponent puts a knight on g5 on move 18.

The move where your prep ends

Here's a test that takes five minutes. Open your last ten games. For each one, find the first move where your opponent played something you had not specifically studied. Write down the move number.

My guess, and it's a guess — I don't have clean data on this and I don't think anyone does at club level — is that most of your numbers are single digits. If your prep runs to move 8 and your opponent leaves it on move 5, the prep was worth three moves of clock time and nothing else.

Worked example. You play the Italian: 1.e4 e5 2.Nf3 Nc6 3.Bc4 Bc5 4.c3, and your opponent replies 4...Qe7. That's not a blunder. It's not in most beginner courses either. You are now on move 5 of a game you were supposedly prepared for, and everything that happens next comes from your general understanding: that your d-pawn wants to get to d4, that the queen on e7 blocks the f8 bishop's retreat and clogs Black's development, that Black's king will have trouble castling short quickly.

That understanding is the actual product. The moves 1-4 were just a way of getting there with a clock advantage.

What to play instead of a repertoire

Pick one first move as White and one answer to each of 1.e4 and 1.d4 as Black. Four total lines, roughly four moves deep each. Not a repertoire — a starting position you recognise. Then stop studying openings and play by rules.

The rules, in priority order when they conflict:

• Every piece gets a job before any piece gets a second one. Knight on b1 is not doing anything on b1.
• Castle by move 10 unless there is a concrete reason not to, and "I want to play an attacking game" is not a concrete reason.
• Don't move the same piece twice in the opening unless you're capturing something, avoiding a capture, or your opponent has just made the position concrete.
• Pawn moves are commitments. e4 and d4 are usually worth it. h3, a3 and g3 usually aren't, unless you can name the piece they're stopping.
• Before you play the natural move, ask what your opponent's last move attacked. This single habit is worth more than any line.

When the repertoire question becomes the right one

It becomes right when you can name the reason you want it. Some real reasons, in rough order of how often they apply:

If none of those apply to you, a repertoire is a way of feeling like you're working. It has the shape of study — there are lines, there's memorisation, there's a sense of a body of knowledge growing — without touching the 9.1% middlegame error rate that is setting your rating.

• You keep reaching the same middlegame and keep not knowing what to do in it. Then you need plans, not more moves — but the plans attach to a specific structure, so you need the structure fixed.
• You lose to the same trap repeatedly. That's a four-move fix, not a repertoire.
• You play a lot of 3+0 or bullet, where fifteen seconds saved on the opening genuinely converts to points.
• You've hit a level where opponents also have prep, and drifting into a bad version of a normal position costs you a real half-pawn before you've thought once.

How to find out what's actually costing you

Take five recent losses. For each, find the move where the evaluation swung by more than about 200 centipawns. Not the moves where you drifted — the one or two where the position changed character. Then look at what phase it was in and what you were doing.

You'll usually find one of four things: you missed that a piece was hanging, you missed a one-move tactic against you, you traded into a worse structure without noticing, or you had no plan and made a pawn move to pass the turn. None of those are opening problems. All four are trainable in a way that shows up in results within a few weeks.

This is the part Mated automates — it pulls your last games from the Chess.com or Lichess API, runs Stockfish over every position in the browser, and rebuilds the positions where you went wrong into a short daily set. But you can do it manually with the analysis board and a notebook. The value is in looking at your own errors repeatedly, not in the tooling.

The thing openings are actually for

Once you stop treating the opening as a memory test, it becomes something more useful: a filter on what kind of middlegame you have to be good at.

If you play the London as White, you will get the same pawn structure most games, and you only need to understand one set of plans deeply. If you play the Sicilian as Black, you will get sharp, unbalanced positions where a single tempo matters, and you'll need to be good at calculation under time pressure. Neither is better. But one of them is better for you, right now, given how you lose.

That's the question worth asking at 1200: not "which opening should I learn" but "which kind of position do I want to be forced into 300 times this year". Answer that and the repertoire builds itself later, four moves at a time, from positions you've already played.