Programming a Chess Engine: Understanding Chess Differently

Programming a chess engine has been a transformative experience. It's given me an opportunity to deepen my understanding of chess in ways that playing alone never could. First lesson I learned: understanding chess engine theory is fundamentally different from playing real-life chess, yet building an engine dramatically improves your practical understanding of the game.

When you play chess, you think in patterns, plans, and intuition:

• "This pawn structure looks weak"
• "I need to castle queenside and launch a pawn storm"
• "That knight on e5 is perfectly placed"

When you program a chess engine, you think in numbers, algorithms, and heuristics:

• "Doubled pawns: -20 centipawns"
• "Iterative deepening to depth 8 with alpha-beta pruning"
• "Knight on outpost: +30 centipawn bonus"

The mathematics isn't the same as the gameplay. A human grandmaster doesn't calculate "this position is +1.43 pawns better." They feel it, they see patterns, they understand it holistically. But here's what surprised me: by forcing myself to quantify chess concepts, I understood them more deeply than ever before.

The first challenge in building an engine is answering a deceptively simple question:

"Who is better, and by how much?"

Humans answer this intuitively. Computers need explicit instructions. Every concept you take for granted must be broken down into measurable components.

The Centipawn: Chess's Universal Currency

Chess engines measure everything in centipawns (cp) — 1/100th of a pawn's value:

+100 cp  = White is ahead by one pawn
-50 cp   = Black is ahead by half a pawn
+300 cp  = White is winning (3 pawn advantage)
±1000 cp = Overwhelming advantage
±100000  = Checkmate

This forced precision changed how I view positions. A "slightly better" position isn't vague anymore—it's quantifiable, debuggable, improvable.

Building an evaluation function taught me that chess breaks down into three categories:

1. Material (40-50% of evaluation)

The baseline. Simple, yet essential:

Pawn:   100 cp (baseline)
Knight: 320 cp (~3 pawns)
Bishop: 330 cp (~3.3 pawns)
Rook:   500 cp (~5 pawns)
Queen:  900 cp (~9 pawns)
King:   20000 cp (infinite — losing it means game over)

What I learned: Even this "simple" concept has nuance. Why is a bishop worth 330 instead of 300? Why is a knight slightly less valuable? These aren't arbitrary—they emerge from decades of engine testing and millions of games. Understanding why these values work taught me to respect piece imbalances more in my own games.

2. Positional Factors (30-40% of evaluation)

This is where it gets interesting:

• Pawn structure
• Piece placement (piece-square tables)
• King safety
• Piece mobility
• Control of the center
• Piece coordination

What I learned: Grandmasters feel these factors. Programming them made me see them. Now when I play, I unconsciously evaluate: "My doubled pawns are worth about -40 centipawns, but my bishop pair compensates for +50." This arithmetic feels unnatural—and yet, thinking this way improved my play.

3. Tactical Factors (10-20% of evaluation)

The dynamic elements:

• Threats and counter-threats
• Pins, forks, skewers
• Discovered attacks
• Static Exchange Evaluation (SEE)

What I learned: Tactics aren't magic tricks—they're patterns your brain learns to recognize. Programming tactical detection made me a better tactician, not through calculation, but throughunderstanding the geometry of piece interactions.

Philidor said: "Pawns are the soul of chess."

I never truly understood this until I programmed pawn structure evaluation.

Why Pawns Are Special

Pawns are unique in chess:

1. They cannot move backward — Every pawn move is a commitment
2. They define the position — They determine where pieces can operate
3. They create permanent weaknesses — A bad pawn structure haunts you forever
4. They control space — They restrict your opponent's pieces
5. They transform — They're the only pieces that can promote

This changed my gameplay immediately. I became more deliberate with pawn moves, treating each one as a strategic commitment.

Doubled Pawns: The Obvious Weakness

Bad structure:          Good structure:
. . . .                 . . . .
. P . .                 . . . .
. P . .                 . P . .
. . . .                 P . . .

Why doubled pawns are bad:

• Both pawns on the same file = they control fewer squares together
• The front pawn blocks the rear one
• The rear pawn is difficult to defend
• Creates "holes" on adjacent files
• Less flexible in pawn endgames

But here's the subtlety: Sometimes doubled pawns are acceptable! If you get the bishop pair in return, an open file for your rook, or control of key central squares, it can be worth it.

Real-world impact: I stopped automatically fearing doubled pawns. I started asking: "What am I getting for this weakness?"

Passed Pawns: The Criminal That Must Be Stopped

Siegbert Tarrasch famously said:

"The passed pawn is a criminal that must be kept under lock and key."

Unstoppable passed pawn:

. . . . . . . K
. . . . . . . .
. . P . . . . .  ← This pawn will queen!
. . . . . . . .
k . . . . . . .

Programming the evaluation of passed pawns taught me something profound: their value increases exponentially as they advance.

Here's how my engine values them:

Rank 7: +120 cp (one square from queening!)
Rank 6: +90 cp  (very dangerous)
Rank 5: +60 cp  (seriously threatening)
Rank 4: +40 cp  (starting to matter)
Rank 3: +30 cp  (long-term asset)
Rank 2: +30 cp  (far from promotion)

Notice the non-linear progression? A passed pawn on the 7th rank is four times more valuable than one on the 3rd rank. This isn't arbitrary—it reflects the real threat level.

Here's the profound thing about building a chess engine:

You're forced to quantify concepts that feel unquantifiable.

• How much is "good king safety" worth? (+50 cp? +100 cp?)
• When does a "slightly better" position become "winning"? (+200 cp? +300 cp?)
• How do you balance three minor pieces vs. a queen? (Queen = 900, three minors = 960, roughly equal)

These questions have no perfect answer. But the process of trying to answer them—of testing, tuning, measuring—gave me a framework for thinking about chess that's both rigorous and flexible.

When you play chess, you think holistically:

• "This position feels better for me"
• "I have more space"
• "My pieces are more active"

When you program chess, you think reductively:

• "I'm ahead by +1.5 pawns"
• "My doubled pawns cost -40 cp, but my bishop pair gives +50 cp, net +10 cp"
• "His passed pawn is worth +90 cp, I need to blockade it or find equivalent compensation"

The paradox: This reductive, mathematical thinking improved my holistic understanding.

Why? Because it forced me to:

1. Be specific — "Better king safety" became "castled king with intact pawn shield = +30 cp"
2. Understand tradeoffs — "This weakness costs X, so I need Y compensation"
3. Think systematically — "Evaluation = material + position + pawn structure + king safety"
4. Test my assumptions — "I thought this was important, but testing shows it barely matters"

Some discoveries were surprising:

Here's what I've come to believe:

Building a chess engine doesn't make you play like a computer. Computers calculate millions of positions per second. Humans never will.

But building an engine makes you think about chess more clearly.

It's like the difference between:

• Speaking a language fluently (playing chess)
• Teaching that language to someone (programming chess)

Teaching forces clarity. Programming forces precision. And precision, paradoxically, leads to deeper intuition.

Now when I play, I still think like a human—in patterns, plans, and intuition. But my intuition is sharper because I've spent time quantifying it. I see doubled pawns and instinctively devalue my position. I see passed pawns and feel their danger proportional to their rank. I see pawn chains and immediately identify the base to attack.

The mathematics isn't the same as the gameplay—but understanding the mathematics improved my gameplay.

Let me share some concrete details about the implementation:

Result: Adding pawn structure evaluation increased my engine's strength by approximately +80-100 ELO points.

That means my engine went from ~1800 ELO to ~1900 ELO just by understanding pawn structure better. If that's not validation of Philidor's quote ("Pawns are the soul of chess"), I don't know what is.

Opening Book Implementation

I also implemented an opening book system with 46 positions covering:

• 1.e4 openings (Ruy Lopez, Sicilian, French, Italian, etc.)
• 1.d4 openings (Queen's Gambit, King's Indian, Nimzo-Indian, etc.)
• Alternative openings (English, Reti)

Result: +100-150 ELO gain. The engine now plays principled opening moves instantly and saves search time for complex middlegame positions.

If you're a chess player (not a programmer), here's what building an engine taught me that you can apply directly:

Chess is beautiful because it can be understood in multiple ways:

• Aesthetically (Mikhail Tal's sacrificial brilliance)
• Logically (Anatoly Karpov's prophylactic perfection)
• Mathematically (modern engines' centipawn calculations)

Building a chess engine didn't make me think like a computer. It made me think more clearly about chess. The mathematics of engines and the intuition of gameplay are different languages—but they describe the same beautiful game.

And learning to translate between those languages has been one of the most rewarding intellectual experiences of my life.

If you're interested in chess, I encourage you to try building an engine. Not because it will make you play like a computer, but because it will make you understand like a teacher.

And there's no better way to learn than to teach.