Chess Openings Lab
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Blackmar-Diemer Gambit Accepted: Gunderam Defense

The Gunderam Defense is 5...Bf5 in the Blackmar-Diemer Gambit Accepted, developing the light-squared bishop outside the pawn chain before ...e6. White usually challenges it with Bd3 to trade bishops and plans Qd3, Bg5 and long castling, while Black builds a sturdy ...e6 and ...c6 shell.

Moves
1.d4 d5 2.e4 dxe4 3.Nc3 Nf6 4.f3 exf3 5.Nxf3 Bf5
ECO
D00
Engine
−0.44 · a slight edge for Black (Stockfish 17.1, depth 20)
Played
234 games in our lichess sample
White scores
48.3%

Key ideas for both sides

White

  • Bd3 offers the bishop trade; after ...Bxd3 and Qxd3 the queen is centralized and eyes b5 and h7.
  • Bg5 with Qd3 and long castling gives pressure down the d-file and against the f6 knight.
  • Ne5 hits f7 and frees the f-file for a rook, a useful idea once the light-squared bishops are traded.

Black

  • ...Bf5 controls e4 and d3, so White cannot set up Bd3 without allowing a bishop trade.
  • After the trade, ...c6, ...e6 and ...Nbd7 give Black a solid Caro-Kann-like setup with the extra pawn.
  • ...h6 against Bg5 asks the bishop to decide, and ...Be7 later breaks the pin on f6.

Plans and pawn structure

After 5...Bf5 the structure is White's d4 pawn against Black pawns on c7 and e7, soon c6 and e6. White has the f-file and more space; Black has an extra pawn and no weaknesses. White's plan is to trade light-squared bishops, castle long and push g4, or use Ne5 and a rook on f1. Black's plan is ...e6, ...c6, ...Be7, ...Nbd7 and short castling, then simplifying.

Where the engine's main line heads: White pawn d4, no e-pawns for White, no d-pawn for Black. White has a pawn on d4 and no e-pawn; Black has no d-pawn. White has more central space; Black's pieces are free and the d4 pawn is a target.

What the engine plays from here

Stockfish 17.1 at depth 20 rates the position −0.44: a slight edge for Black. Its three top choices for White:

  1. −0.44 6.Bg5 h6 7.Bh4 e6 8.Bd3 Bxd3
  2. −0.47 6.Bd3 Bxd3 7.Qxd3 c6 8.Bg5 e6
  3. −0.60 6.a3 e6 7.Bd3 Bxd3 8.Qxd3 Nbd7

Pawns, from White's side.

How it scores on lichess

234 rated lichess games reached this position; White scored 48.3%.

1200–159951.5%
1600–199944.0%
2000 and up48.8%

Light: White wins. Grey: draws. Dark: Black wins. About the sample.

Where it goes next

  • Gunderam Defense, Stader Variation6.Ne5 · rare

How to play against it

As White, play Bd3 or Bg5 at once; the bishop on f5 is Black's most active piece and trading it eases your play. After the bishop trade, Qd3 and long castling are the natural plan. Do not let Black finish development in peace.

Questions

What are the moves of the Blackmar-Diemer Gambit Accepted: Gunderam Defense?

The Blackmar-Diemer Gambit Accepted: Gunderam Defense starts 1.d4 d5 2.e4 dxe4 3.Nc3 Nf6 4.f3 exf3 5.Nxf3 Bf5. Its ECO code is D00.

Is the Blackmar-Diemer Gambit Accepted: Gunderam Defense good for Black?

Stockfish 17.1 rates the position −0.44 at depth 20, which is a slight edge for Black. In 234 lichess games from our sample, White scored 48.3%. A sound defense for Black players who like a Caro-Kann structure; White needs a clear plan after the bishop trade.

What is the main idea of the Blackmar-Diemer Gambit Accepted: Gunderam Defense?

Black develops the light-squared bishop actively before ...e6, then builds a Caro-Kann-like shell with ...c6 and ...e6. White aims to trade that bishop with Bd3 and attack with long castling.

What should White play next?

The engine's first choice is Bg5, with Bd3 and a3 close behind. 6.Bg5 pins the f6 knight and develops toward long castling before Black finishes with ...e6.

Updated October 2026. Sources and method.