Build a Local RAG Chatbot in 30 Minutes with .NET 8, Ollama, and React

I uploaded a 40-page PDF of an internal API spec, asked "what's the rate limit for the search endpoint?", and got back: "100 requests per minute per API key, with bursts up to 200. See section 4.2 of the document." With citations. In about three seconds. The whole stack runs on my laptop. It cost me $0 in LLM credits during development because Ollama is free and local, and the embedder I used is also free and local. The repo is here — issues and PRs welcome. This is the build log. Not a tutorial where every step works the first time — a build log where I tell you which decisions held up and which ones I redid. The problem most "chat with your PDF" demos have Every "chat with your PDF" tutorial I read in early 2025 had the same shape: open OpenAI, paste your API key, call gpt-4 with a 50-page PDF stuffed into the context window, get an answer, pay $0.03 per question, repeat. That works for a demo. It does not work for a tool you'd actually use at work, because: The PDF might contain customer data, internal pricing, or unreleased features. You do not want that going to OpenAI's training pipeline or anyone's logs. The cost adds up. If your team uses it 50 times a day, that's $45/month per seat. The model hallucinates on long PDFs anyway. Stuff 100 pages into a 128k context window and the model starts forgetting the middle. The fix is RAG (Retrieval-Augmented Generation) — don't send the whole PDF, send only the 3-5 chunks that are actually relevant to the question. The rest of the work is the same: embed the chunks, embed the question, find the closest matches, send those to the LLM with the question. But the cost and the privacy story both improve by 100x. The actual ask: Upload a PDF. Ask questions. Get answers from the document with citations, in under 5 seconds, with no data leaving my laptop and no monthly bill. The architecture One .NET 8 solution, one React app, one Ollama process, zero cloud dependencies. [ PDF Upload ] | v +-------------------+ chunks +-------