World's Fair 2025
How LLMs work for Web Devs: GPT in 600 lines of Vanilla JS - Ishan Anand
Overview
This talk breaks down how Large Language Models (LLMs) like GPT-2 work, demystifying them for web developers by implementing a core GPT-2 model in approximately 600 lines of vanilla JavaScript. The presentation emphasizes understanding the underlying mechanics rather than requiring deep ML expertise, using analogies and code walkthroughs to make complex concepts accessible. The goal is to transform the perception of LLMs from magic to understandable machinery.
Who should watch
- AI Engineers
- Product Managers
- Web Developers with JavaScript backgrounds
- Builders interested in understanding LLM internals
- Anyone curious about how LLMs generate text
Key takeaways
- LLMs fundamentally predict the next word (or token) in a sequence, operating auto-regressively by feeding their output back as input.
- Sub-word tokenization (like Byte Pair Encoding) is used to efficiently represent text, balancing vocabulary size and sequence length compared to word or character-level methods.
- Embeddings convert tokens into numerical representations (vectors) that capture semantic meaning, allowing for mathematical operations that reveal word relationships.
- Positional embeddings are added to token embeddings to preserve word order information, which is crucial for understanding sentence structure and meaning.
- The attention mechanism allows tokens to weigh the relevance of other tokens in the sequence, enabling the model to disambiguate meaning and understand context.
- Multi-layer perceptrons (MLPs) within the model layers perform complex computations, acting as universal function approximators trained via backpropagation.
- The process of training LLMs involves learning from vast amounts of text, optimizing parameters through backpropagation to minimize prediction errors.
- Modern chatbots like ChatGPT differ from base models like GPT-2 not just in scale but significantly in their training objectives, incorporating instruction following and reinforcement learning from human feedback (RLHF) to align with user intent.
Notable quotes
*Any sufficiently advanced technology is indistinguishable from magic.*
*If you understand GPT-2, you are 80% of the way to understanding how a state-of-the-art model works under the hood.*
*You shall know a word by the company it keeps.*
Unofficial community note. Prefer the recording for nuance.