London System traps: 6 mistakes at 1600-1800 Elo

October 9, 2026 · 4 min read

At 1600-1800 the obvious blunders are gone. Black fights back with ...c5, ...Qb6 and ...e5, and White mixes the slow London with sharper tries like Nc3, e4 and Ne5. The mistakes are about timing: a queen that leaves home a move too early, a pawn break that opens a file for the other side, or a jump that leaves b2 or e5 without a guard.

We took the Lichess blitz and rapid games from August 2026 where both players were rated 1600 to 1800, followed the London move by move, and had Stockfish check every position where many players took the same wrong turn. Every line below was verified by the engine. All six examples are told from White’s side. For the main ideas of the opening, read our London System guide. One level down, see 6 mistakes at 1400-1600 Elo; one level up, 6 mistakes at 1800-2000 Elo.

Part 1: punish it

Three Black mistakes, three punishments. The first two are about squares the black queen or pawns stopped guarding. The third is about a bishop Black gave away too cheaply.

1. 4...Qb6, and the queen leaves d5 behind

After 1.d4 d5 2.Bf4 c5 3.e3 Nc6 4.Nf3, 9% of Black players go after b2 with 4...Qb6. But on d8 the queen was guarding d5 and c7. 5.Nc3! threatens both 6.Nxd5 and 6.Nb5 with Nc7+. If 5...e6, 6.Nb5 c4 7.Nc7+ Kd8 8.Nxa8 wins a rook. If 5...Qxb2, 6.Nxd5 is even worse for Black. The best try is 5...Qa5 6.dxc5 Nf6 7.Bb5, and White is a pawn up. Only 1 of the 17 White players found 5.Nc3; most defended with 5.b3.

Black should play 4...cxd4 instead, and the game is balanced.

4...Qb6? and 5.Nc3! wins a pawn.

2. 5...e5 after ...f6

After 1.d4 d5 2.Bf4 Nc6 3.e3 Bf5 4.Nf3 f6 5.c3, 29% of Black players follow up with 5...e5. It looks like the point of ...f6, but it comes one move too early. After 6.dxe5 fxe5, the pawn on e5 is attacked by the knight and the bishop and guarded only by the knight on c6. 7.Nxe5 Nxe5 8.Bxe5, and White is a pawn up. All ten White players in our sample took on e5.

Black should prepare with 5...g5 or 5...e6 instead. The game is balanced.

5...e5? and 6.dxe5! wins a pawn.

3. 5...Bxe5, and g7 loses its guard

After 1.d4 d5 2.Bf4 Nf6 3.e3 e6 4.Nf3 Bd6 5.Ne5, 13% of Black players take the knight with 5...Bxe5. Take back with 6.dxe5!: the pawn hits the knight on f6, and the bishop that guarded the dark squares around the black king is gone. After 6...Nfd7, the most common reply, 7.Qg4! hits g7, and Black has to guard it with 7...Rg8 instead of castling. White is clearly better. Only half of the White players took back with the pawn.

Black should castle with 5...O-O instead, and the game is balanced.

5...Bxe5? and 6.dxe5! then 7.Qg4!

Part 2: avoid it

Now the White mistakes that come up most in the London at 1600-1800. In all three, White plays an active move and gives Black a target: a knight with no squares, a pawn with no defender, or an open b2.

4. 4.Nc3 after 3.dxc5

After 1.d4 d5 2.Bf4 c5 3.dxc5 Nc6, 19% of White players develop with 4.Nc3. But the knight stands in front of the black d-pawn. 4...d4! kicks it, and it has no good square. After 5.Na4 Qa5+ 6.c3 b5 7.Bd2 Nf6 8.cxd4 Qxa4, Black has won the knight for two pawns.

Play 4.Nf3 instead. Develop, keep the c5 pawn for now, and the game is balanced.

4.Nc3? and 4...d4! Play 4.Nf3 instead.

5. 5.e5 against the Pirc setup

After 1.d4 Nf6 2.Bf4 d6 3.Nc3 g6 4.e4 Bg7, 9% of White players push 5.e5. But the pawn on e5 leans on the bishop on f4, and the bishop can be chased. 5...Nh5! hits it. After 6.Bd2 dxe5 7.dxe5 Bxe5, Black is a pawn up. Almost every Black player answered 5...dxe5, which is fine for White. Only 1 of 22 found 5...Nh5.

Play 5.Qd2 instead. Keep the pawn on e4, aim at h6, and White is a little better.

5.e5? and 5...Nh5! Play 5.Qd2 instead.

6. 6.Ne5 when the queen can check on b4

After 1.d4 d5 2.Bf4 e6 3.e3 Bd6 4.Nf3 Bxf4 5.exf4 Qd6, 25% of White players jump with 6.Ne5. But the queen on d1 was the only guard of b2. 6...Qb4+! checks and hits b2. After 7.Nc3 Qxb2 8.Nb5 Qb4+ 9.Qd2 Qxd2+ 10.Kxd2 Na6, the queens are off and Black has an extra pawn. White has some activity, but not enough for it.

Play 6.Qd2 instead. The queen guards b2 and f4, and the game is balanced.

6.Ne5? and 6...Qb4+! Play 6.Qd2 instead.

What to take away

When the black queen leaves d8 early, look at d5 and c7: Nc3 and Nb5 may hit both.
After ...f6 and ...e5, count attackers on e5 once the pawns are traded.
If Black gives up the dark bishop on e5, take back with the pawn and look at g7.
Before an active knight or pawn move, check what the queen or bishop stops guarding: b2, e5, or the squares in front of the knight.

These patterns come from many games between players at your level, not from a theory book. Your own games have patterns too, and they are probably not the same ones. Chess X-Ray finds the moves where you lost your advantage in your chess.com or Lichess games, groups them by opening, and turns them into lessons you replay until they stick.