Fine-tuning an LLM to write docs like it's 1995

In my predictions for 2030 I wrote that tech writers would be using specialized LLMs, running locally on powerful hardware. I see hints of this move to “local first” among engineering pundits, but we’re not there yet, in part because of how much more powerful connected frontier models are. That doesn’t mean we can’t experiment, though. That’s precisely what I did last week, trying to fine-tune an instruct model to write like a software technical writer from the 80s and 90s.

Summoning old tech writing lore for research

To train a personal, local model to write like a technical writer from the 90s, one needs tons of written sources. If I wanted to fine-tune a model to write like myself, for example, this blog would not be enough, as it’s barely 100k words at the time of this post. You would need more samples for thorough training, and those are not easy to come by, nor simple to produce. The only quick way is to use an existing corpus. Where could I get one?

Meet Bitsavers: it’s a website that collects and scans old computer manuals and brochures. It’s an incredibly valuable repository of computer history and ancient tech writing, with mirrors available everywhere. As I’m fond of Microsoft manuals from the 90s, I chose the Microsoft collection as the source of training materials. The collection contains out-of-print docs published between 1977 and 2005: more than 37 million words, covering old systems and SDKs.

I downloaded the OCR’d text files and cleaned the content from artifacts and clutter (like indices and frontmatter) using good old Python scripts. I then used a cheap and fast model through OpenRouter, gemma-4-26b, to classify each paragraph as either “keep” or “drop” based on its intelligibility. This second pass cost around 8 dollars. Even with this two-pass cleaning, though, training data retained noise that I discovered only later, but that was largely OK for my tests.

I split the sanitized text into training examples on paragraph and section boundaries, breaking at headings and keeping code blocks whole, with each chunk capped at around 512 tokens as per Claude advice. Each chunk was paired with a synthetic instruction drawn from templates. I ended up with 192,456 examples in JSONL format (one JSON object per line). I could have used a small model to also come up with better instructions and questions, but I’m an impatient person.

💡 A note on the materials: This is an independent, non-commercial research project and is not affiliated with, sponsored, or endorsed by Microsoft. I used these out-of-print manuals for personal style-transfer experimentation only. The corpus, training data, and resulting adapters are not being distributed, and the fine-tuned models remain strictly local to my machine.

Fine-tuning as an alternative to training from scratch

In an ideal world, I would have several millions of dollars lying around, ready to be burned creating my own LLM, Fabrice. Since I’m far from rich (I wouldn’t be writing this otherwise), the alternative to Fabrice is fine-tuning, which involves tweaking the “weights” of a model so that each token generated is conditioned by the training materials. I like to picture fine-tuning as slightly steering the trajectory of a massive iceberg using tugs; just a little, just to get the intended effect.

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