20EQ

A Halloween-themed command-line chatbot game in the spirit of 20 Questions — except the spooky teen-coded character on the other side of the void is secretly running an information-theoretic profile of you over ~20 turns. When the candle goes out, she drops the act and reveals her dossier.

Written in Harn.

Install

You need two things on your machine:

1. The Harn toolchain. Install the exact version in .harn-version from crates.io:

cargo install harn-cli --version 0.10.131 --locked

That puts a harn binary in ~/.cargo/bin/. Run harn --version to confirm it reports harn 0.10.131.

2. A local OpenAI-compatible chat server with a model loaded. Harn discovers common local servers automatically. Set LOCAL_LLM_BASE_URL when yours uses a non-default address, and give it the server root without the /v1 suffix, which Harn appends itself (http://127.0.0.1:8001, not http://127.0.0.1:8001/v1). The game defaults to local:qwen3.6-35b-a3b-ud-q4-k-xl; override it without editing source by setting TWENTY_EQ_MODEL to any Harn model id, such as ollama:qwen3.5:9b.

Spot-checked against Qwen3.6-35B-A3B on llama.cpp. Harn treats a local: model id as the generic OpenAI-compatible adapter and ollama: as Ollama, so switching between llama.cpp, Ollama, vLLM, and MLX is a TWENTY_EQ_MODEL change rather than a source edit.

Play

harn run 20eq.harn

Type /quit to bail early; otherwise the candle goes out on its own after 20 turns and the dossier drops.

Files

• 20eq.harn — the terminal game and character prompt; pub fn main(harness: Harness) is the entry point
• lib/game.harn — deterministic turn policy, model routing, and private-text boundary
• tests/game_test.harn — six fast in-process cases with no model call and no wall clock
• harn.toml — Harn package manifest, including the supported Harn range
• .harn-version — the exact Harn toolchain this repository is verified against
• .github/workflows/ci.yml — package and test verification
• CONTRIBUTING.md, LICENSE, README.md, .gitignore — contributor guide and boilerplate

Develop

Run the same deterministic checks as CI:

harn fmt --check 20eq.harn lib/game.harn tests/game_test.harn
harn check --strict-types 20eq.harn lib/game.harn tests/game_test.harn
harn lint --strict 20eq.harn lib/game.harn tests/game_test.harn
harn test tests/ --parallel
harn package check

harn test takes one positional target, so run the suite as harn test tests/. The six cases are all deterministic: the streaming case uses harness.llm.mock_enqueue, and nothing else reaches a model.

No Git hook is required. Editors and agents can format with harn fmt, while CI remains the authoritative gate.

License

MIT — see LICENSE. Covers the contents of this repository only. Harn is a separate project under its own dual Apache-2.0/MIT license, and any local LLM weights you point this at are governed by their own terms.