--- title: Decoder-Only Transformers From Scratch: What Building... description: A personal learning journal documenting the journey of building a decoder-only transformer model from scratch, culminating in ChessGPT — a chess move... canonical: https://daily.dev/posts/decoder-only-transformers-from-scratch-what-building-chessgpt-taught-me-hzjxavwxv twitter:card: summary_large_image twitter:site: @dailydotdev og:type: website og:site_name: daily.dev og:title: Decoder-Only Transformers From Scratch: What Building ChessGPT Taught Me | daily.dev og:description: A personal learning journal documenting the journey of building a decoder-only transformer model from scratch, culminating in ChessGPT — a chess move... og:url: https://daily.dev/posts/decoder-only-transformers-from-scratch-what-building-chessgpt-taught-me-hzjxavwxv og:image: https://api.daily.dev/og/posts/hzjxavWxv.png og:image:alt: Decoder-Only Transformers From Scratch: What Building ChessGPT Taught Me og:image:width: 1200 og:image:height: 630 og:locale: en --- > ## Documentation Index > Fetch the complete documentation index at: https://daily.dev/llms.txt > Use this file to discover all available pages before exploring further. # Decoder-Only Transformers From Scratch: What Building ChessGPT Taught Me **[Medium](https://daily.dev/sources/medium_js)** · 12 min read · 0 upvotes · 0 comments ## Summary A personal learning journal documenting the journey of building a decoder-only transformer model from scratch, culminating in ChessGPT — a chess move prediction model. Covers the author's path from Stanford CS224N through hands-on implementation, including decisions around chess notation formats (PGN vs UCI), vocabulary design, tokenization, masked self-attention, positional embeddings, and training on ~10,000–30,000 chess games with an RTX 3060. Key lessons include PyTorch's automatic backpropagation, the importance of positional embeddings, the auto-regressive vs non-auto-regressive behavior of decoders at inference vs training, and the limitations of overfitting on small datasets. ## Full article daily.dev links to this article rather than hosting it. Read it at the original source: ## Similar posts on daily.dev - [Building GPT from Scratch: What I Learned Implementing a Transformer in Raw PyTorch](https://daily.dev/posts/building-gpt-from-scratch-what-i-learned-implementing-a-transformer-in-raw-pytorch-janzjl2vo) · Medium · 3 upvotes · 0 comments - [Creating a Llama or GPT Model for Next-Token Prediction](https://daily.dev/posts/creating-a-llama-or-gpt-model-for-next-token-prediction-gvhas02dv) · Machine Learning Mastery · 0 upvotes · 0 comments --- Tags: [#deep-learning](https://daily.dev/tags/deep-learning), [#nlp](https://daily.dev/tags/nlp), [#pytorch](https://daily.dev/tags/pytorch) [View this post on daily.dev](https://daily.dev/posts/decoder-only-transformers-from-scratch-what-building-chessgpt-taught-me-hzjxavwxv) ```json {"@context":"https://schema.org","@graph":[{"@type":"Organization","@id":"https://daily.dev/#organization","name":"daily.dev","url":"https://daily.dev","logo":{"@type":"ImageObject","url":"https://daily.dev/apple-touch-icon.png","width":180,"height":180},"sameAs":["https://twitter.com/dailydotdev","https://github.com/dailydotdev","https://www.linkedin.com/company/daily-dev-ltd"]},{"@type":"WebSite","@id":"https://daily.dev/#website","url":"https://daily.dev","name":"daily.dev","publisher":{"@id":"https://daily.dev/#organization"},"potentialAction":{"@type":"SearchAction","target":{"@type":"EntryPoint","urlTemplate":"https://daily.dev/search?q={search_term_string}"},"query-input":"required name=search_term_string"}}]} {"@context":"https://schema.org","@type":"TechArticle","headline":"Decoder-Only Transformers From Scratch: What Building ChessGPT Taught Me","url":"https://daily.dev/posts/decoder-only-transformers-from-scratch-what-building-chessgpt-taught-me-hzjxavwxv","mainEntityOfPage":{"@type":"WebPage","@id":"https://daily.dev/posts/decoder-only-transformers-from-scratch-what-building-chessgpt-taught-me-hzjxavwxv"},"datePublished":"2026-07-18T06:47:43.012Z","dateModified":"2026-07-18T06:48:37.557Z","description":"A personal learning journal documenting the journey of building a decoder-only transformer model from scratch, culminating in ChessGPT — a chess move...","image":"https://media.daily.dev/image/upload/f_auto,q_auto/v1/posts/3b90d8cd29a6f2cacf8249a5de68991d?_a=AQAEuop","thumbnailUrl":"https://media.daily.dev/image/upload/f_auto,q_auto/v1/posts/3b90d8cd29a6f2cacf8249a5de68991d?_a=AQAEuop","isAccessibleForFree":true,"articleSection":"Medium","inLanguage":"en","publisher":{"@type":"Organization","name":"daily.dev","url":"https://daily.dev","logo":{"@type":"ImageObject","url":"https://daily.dev/apple-touch-icon.png","width":180,"height":180}},"author":{"@type":"Organization","name":"Medium","logo":"https://media.daily.dev/image/upload/t_logo,f_auto/v1/logos/medium","url":"https://daily.dev/sources/medium_js"},"commentCount":0,"discussionUrl":"https://daily.dev/posts/decoder-only-transformers-from-scratch-what-building-chessgpt-taught-me-hzjxavwxv","interactionStatistic":[{"@type":"InteractionCounter","interactionType":{"@type":"LikeAction"},"userInteractionCount":0},{"@type":"InteractionCounter","interactionType":{"@type":"CommentAction"},"userInteractionCount":0}],"keywords":"deep-learning,nlp,pytorch","timeRequired":"PT12M"} {"@context":"https://schema.org","@type":"BreadcrumbList","itemListElement":[{"@type":"ListItem","position":1,"name":"Home","item":"https://daily.dev"},{"@type":"ListItem","position":2,"name":"Medium","item":"https://daily.dev/sources/medium_js"},{"@type":"ListItem","position":3,"name":"Decoder-Only Transformers From Scratch: What Building ChessGPT Taught Me"}]} ```