NEAT Config File Tutorial - Interactive 10-Minute Lesson for Kids

🤖 Robots & Fitness

👀 Inputs & Outputs

🧬 Mutation

🎯 Species & Stagnation

📝 Quick Quiz

🤖 Step 1: Robots & Fitness (Score)

NEAT makes a bunch of “robot players” (AI agents). Each robot plays the same level one at a time. The robot earns a fitness score (like points). High score = better robot! 🏆

⚙️ Config Snippet

[NEAT]

pop_size = 200 # robots per generation

fitness_threshold = 600 # stop when reached

fitness_criterion = max # higher is better

pop_size (robots in a generation): 200

fitness_threshold (goal score): 600

You’re simulating: robots play → scores saved → best survive → babies created 🔄

🎮 Mini Simulator

Generation

Best Fitness

Status

Waiting

Click “Run 1 Generation” to see what happens…

Step complete: No

👀 Step 2: Inputs & Outputs (Eyes & Buttons)

The AI needs inputs (what it can see) and produces outputs (what buttons it presses). Your config says the robot has 9 inputs and 3 outputs. 🎮

⚙️ Config Snippet

[DefaultGenome]

num_inputs = 9

num_outputs = 3

num_inputs: 9

Examples: distance to enemy, is on ground?, speed, gap ahead…

num_outputs: 3

Examples: move left, move right, jump, shoot…

🎯 Try It: Map Outputs to Game Buttons

Pick what the 3 outputs mean for your platform game:

Output #1

Move Left Move Right Jump

Output #2

Move Left Move Right Jump

Output #3

Move Left Move Right Jump

Step complete: No

🧬 Step 3: Mutation (How Robots Change)

After one generation, NEAT keeps the better robots and makes new robots by copying them… then adds small random changes called mutations. That’s how robots “evolve.”

⚙️ Config Snippet

[DefaultGenome]

weight_mutate_rate = 0.55

node_add_prob = 0.20

conn_add_prob = 0.20

weight_mutate_rate (change brain numbers): 0.55

node_add_prob (add new neuron): 0.20

conn_add_prob (add new wire): 0.20

🧪 Try It: Evolve a New Generation

Press the button to “make babies” from the best robot. We’ll show how mutation settings change results.

Step complete: No

Tip: If mutation is too low, robots don’t change much. If too high, robots become random.

4) Species & Stagnation (Teams and “No Improvement”)

NEAT splits robots into species (teams of similar brains) so one strategy doesn’t dominate too early. If a species stops improving, NEAT can remove it (stagnation).

Config Snippet

[DefaultSpeciesSet]

compatibility_threshold = 1.485

[DefaultStagnation]

max_stagnation = 5

species_elitism = 2

• Lower compatibility threshold → more species (more teams)
• Higher threshold → fewer species (bigger teams)

Mini Challenge: Keep Diversity

Choose the best explanation for why we use species.

So robots can play multiplayer together So similar robots compete in teams and different ideas don’t disappear too fast So the game runs faster

Step complete: No

5) Quick Quiz (2 minutes)

Answer these 4 questions. If you score 3/4 or higher, you completed the lesson ✅

1) What does `pop_size = 200` mean?

200 enemies spawn 200 robots are tested per generation 200 levels are loaded

2) What are `num_inputs` and `num_outputs`?

Player health and score Enemy speed settings The AI’s sensors (inputs) and action buttons (outputs)

3) What does a “mutation” do?

Randomly changes the robot brain a little so new ideas appear Deletes the game code Makes the robot cheat

4) Why does NEAT use “species”?

To make robots talk to each other To keep different strategies alive instead of one dominating too early To increase screen resolution

Score: 0/4 Lesson complete: No

Takeaway (What the config really is)

This file is the rulebook for evolving robot brains: how many robots, how scoring works, how robots mutate, and how diversity is kept. It does not draw the game or change physics—only the AI evolution rules.

🤖 Step 1: Robots & Fitness (Score)

⚙️ Config Snippet

🎮 Mini Simulator

👀 Step 2: Inputs & Outputs (Eyes & Buttons)

⚙️ Config Snippet

🎯 Try It: Map Outputs to Game Buttons

Output #1

Output #2

Output #3

🧬 Step 3: Mutation (How Robots Change)

⚙️ Config Snippet

🧪 Try It: Evolve a New Generation

4) Species & Stagnation (Teams and “No Improvement”)

Config Snippet

Mini Challenge: Keep Diversity

5) Quick Quiz (2 minutes)

1) What does pop_size = 200 mean?

2) What are num_inputs and num_outputs?

3) What does a “mutation” do?

4) Why does NEAT use “species”?

Takeaway (What the config really is)

1) What does `pop_size = 200` mean?

2) What are `num_inputs` and `num_outputs`?