Building a Small Language Model from Scratch in Python

We ‘re now moving from theory and deployment into hands-on Python implementation — showing “how to actually build a small language model from scratch“.

Here’s a table of contents (15 articles) that focuses on building a small language model from scratch as a tutorial.

Part 1: Foundations — From Text to Tokens

  1. Introduction: What Is a Small Language Model (SLM)?
    → Explain architecture, tokenization, and what makes “small” models special.
  2. Collecting and Cleaning Your Dataset
    → Use open text sources (TinyStories, Gutenberg, wikitext). Show cleaning & normalization in Python.
  3. Building a Simple Tokenizer from Scratch
    → Implement Byte-Pair Encoding (BPE) or WordPiece tokenizer in Python — step by step.
  4. Converting Text into Numerical Data
    → Create a vocabulary, encode text into token IDs, and build a dataloader with PyTorch.

Part 2: Architecture — Building the Brain

  1. Building a Tiny Transformer in PyTorch
    → Define embeddings, attention, feedforward, and layer normalization manually.
  2. Understanding Multi-Head Attention (Visually and in Code)
    → Break down query/key/value matrices, masking, and head aggregation.
  3. Implementing Positional Encoding and Model Forward Pass
    → Add positional context and run your first forward pass.
  4. Training Loop: Teaching the Model to Predict the Next Token
    → Use cross-entropy loss, batching, and gradient descent to train your SLM.

Part 3: Scaling and Evaluation

  1. Generating Text: From Training to Inference
    → Implement greedy and temperature-based sampling.
  2. Evaluating Performance: Loss Curves and Perplexity
    → Plot training progress and measure model quality.
  3. Optimizing for Speed and Size (Quantization + Mixed Precision)
    → Demonstrate how to shrink model weights using bitsandbytes or PyTorch’s quantization.
  4. Saving and Reloading Your Model Efficiently
    → Cover checkpoints, weight saving, and versioning for reproducibility.

Part 4: Beyond the Basics

  1. Fine-Tuning Your Small Model on Custom Data
    → Show how to adapt your base SLM to specific text domains.
  2. Adding a Simple Chat Interface (Streamlit or FastAPI)
    → Turn the trained model into a mini local chatbot UI.
  3. Deploying Your SLM as a GGUF Model (for llama.cpp or Ollama)
    → Export and test your model in small inference environments.

💡 Optional Bonus Tutorials

  • “Visualizing Attention Heads in Your Own Model”
  • “Adding Memory to a Custom SLM”
  • “Comparing Your Model to TinyLlama and Phi-3 Mini”

The code Small Language Model we’re building is here available on Github.

Follow NanoLanguageModels.com to continue the full “Build a Small Language Model from Scratch” series — next up: What Is a Small Language Model (SLM)? ⚙️

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