Rozumnyk

Rozumnyk (Ukrainian розумник — “the clever one”) — a self-hosted, streaming ChatGPT-style assistant powered by Claude. Your key, your data, no middleman.

A single-file Node server + a clean web UI. Token-by-token streaming over SSE, swappable system-prompt presets, conversation memory in the browser. Nothing leaves your machine except the call to Anthropic with your own API key.

Features

• Streaming responses (Server-Sent Events) — text appears as it’s generated.
• Presets — default, coder, editor; switch the assistant’s behaviour live.
• Prompt caching on the system prompt — repeated turns are cheaper and faster.
• Zero storage — history lives in the browser tab, not on disk.
• ~150 lines of server, no framework lock-in, no build step.

Run

npm install
export ANTHROPIC_API_KEY=sk-ant-...      # Windows: set ANTHROPIC_API_KEY=...
npm start
# open http://localhost:8787

Optional env: PORT (default 8787), ROZUMNYK_MODEL (default claude-sonnet-4-6).

Stack

Node.js · Express · @anthropic-ai/sdk · SSE streaming · vanilla front-end.

License

MIT © Oleksandr Bilov (@Dominant-dev)