Hoshi 星
A Go board that feels every move.
A free desktop app to play and study Go (Baduk, Weiqi): a beautiful board, KataGo built in,
joseki guidance, engines, and online play on OGS.
Website · Download · Features · Support · Build it yourself
Download
Ready-to-run builds, no .NET needed. The desktop installers keep Hoshi up to date by themselves (small delta updates).
Windows may show a SmartScreen warning for new, unsigned apps: More info → Run anyway.
KataGo comes with the Windows, Linux x64 and Android downloads; elsewhere Hoshi installs it in one click.
Android: Hoshi is not on Google Play yet. Open the APK and allow your browser to install apps; if Play Protect warns, choose Install anyway. To update, install the new APK over the old one. On the phone you tap a point, then tap it again to play.
Features
🔍 Study with KataGo
KataGo runs in the background from the moment Hoshi opens and rates every move — best, excellent, good,
inaccuracy, mistake or blunder — with points lost, win rate, score graph and suggestions on the board.
A full SGF editor with variation tree, comments, marks and setup stones.
📝 Review together
Press S in any game to pin the moments that mattered — mistake, good move, question, key moment,
joseki, life and death, lesson — and draw arrows, areas, letters and numbered "what if" lines without
touching the game. Save the study as an SGF and send it: your friend's notes and replies merge into yours.
Then test yourself with What would you play? or print a game report with KataGo's verdict on each moment.
⚙️ Play any engine
Hoshi's own KataGo is ready out of the box; add Leela Zero, GNU Go, Pachi or any GTP engine.
Play against it (Ctrl+G) with any colour, handicap, komi and rules, let two engines play each other,
watch the traffic in the GTP console, or let your engine drive the analysis panel.
📐 Never forget a joseki
Turn on Joseki and every corner shows the known continuations, coloured by how the OGS Joseki Explorer
rates them. The trainer (Ctrl+J) drills lines on the main board with spaced repetition.
✦ A board that feels
The move that wins a fight shakes the board and cracks the wood; routine moves just click. Weak groups glow
faintly, captured stones shatter, and calm lo-fi music heats up at the key moments. Too much? Turn effects
down to subtle or off at any time with F.
🌐 Play online
Sign in to online-go.com, accept challenges and play in real time with clock and chat.
Fair play first: Hoshi only creates unranked games, and every engine, hint and analysis switches off during
your live OGS games.
🎨 Make it yours
Five themes — Night sky, Ink and gold, Zen garden, Warm minimal and a Classic tribute — plus six gobans,
five stone sets and ten backgrounds to mix freely. Every board and stone is rendered by Hoshi itself.
English and Spanish.
Also: a library of every game you play (replay it and KataGo judges each move again), territory estimate,
face-to-face games on one screen, keyboard shortcuts, automatic updates. Free, open source, no account needed
to play locally, and your OGS password is never stored.
Support Hoshi
Hoshi is free and open source, and will stay that way. If it brings you good games and you'd like to help it grow,
you can make a donation on PayPal ♥. It is entirely optional — nothing
in Hoshi depends on it. Thank you either way.
A note on where donations go: PayPal isn't available where I live, so donations are received on my behalf by
a trusted collaborator, Carlos Fernandez — that's the name you'll see on the PayPal page.
Feedback is just as welcome: open an issue with a bug, an idea or
something that feels off. GTP engine support came from a player's comment.
For developers
Built with Avalonia 11 on .NET 10 (C# 14), MVVM with CommunityToolkit.Mvvm. Status and plans:
docs/ROADMAP.md · architecture: docs/ARCHITECTURE.md ·
visual design: docs/DESIGN.md · OGS notes: docs/OGS_API.md.
Build, test, run
Requires the .NET SDK 10.0 (global.json pins the minimum feature band 10.0.100).
Hoshi.sln includes the Android app, which needs the Android workload (dotnet workload install android);
Hoshi.Desktop.slnf is the same solution without it, for the desktop app and the tests (what CI builds).
dotnet build Hoshi.Desktop.slnf
dotnet test Hoshi.Desktop.slnf
dotnet run --project src/Hoshi.Desktop
Logs are written to the per-user data folder (%LOCALAPPDATA%\Hoshi\logs on Windows,
~/Library/Application Support/Hoshi/logs on macOS, ~/.local/share/Hoshi/logs on Linux).
Layout
src/
Hoshi.Core/ Pure Go rules: captures, ko, scoring, fights, group strength (no UI, no I/O)
Hoshi.Sgf/ SGF parser/serializer and game tree
Hoshi.Ogs/ online-go.com client (OAuth + PKCE, REST, WebSocket)
Hoshi.Engines/ KataGo analysis engine (JSON) and a GTP client for any engine
Hoshi.App/ Avalonia application (shared library: views, view models, controls)
Hoshi.Desktop/ Desktop executable (Windows, macOS, Linux)
Hoshi.Android/ Android app (built by .github/workflows/android.yml; needs the Android workload)
tests/ xUnit + FluentAssertions, Avalonia.Headless for UI
docs/ Architecture, design, OGS API notes, roadmap; docs/site is the website
Dependency rule: App → Ogs, Sgf, Engines, Core · Ogs → Core · Sgf → Core · Engines → Core · Core → nothing
(enforced by tests/Hoshi.App.Tests/ArchitectureTests.cs).
Releases and website
.github/workflows/release.yml builds and publishes the installers (Velopack) once CI has passed on main
(version 0.1.<run number>; nothing is published when only docs/, .github/ or Markdown files changed).
The website in docs/site is published by .github/workflows/pages.yml.
Development against OGS
Pick the server in the lobby (Ctrl+L or "Online"); it does not depend on the .NET environment.
| Server | Sign-in |
|---|
https://online-go.com (default) | "Continue with Google" or "Sign in with OGS": browser OAuth (authorization code + PKCE, public client, redirect http://127.0.0.1:8734/callback). |
https://beta.online-go.com (testing) | Username + password (beta cannot register OAuth apps). The password is never stored. |
"Continue with Google" always uses online-go.com. There: unranked, private games against your own second
account only. Hoshi never creates or accepts ranked games. Set Ogs:DefaultServer to beta in appsettings.json
to start on beta. No secrets live in the repository: the OAuth client id is public.
Credits
Inspired by Sabaki, whose look and feel we love — no Sabaki code is used.
Third-party assets and their licenses are listed in THIRD_PARTY_NOTICES.md.
