The details
Plain facts
Everything the front page leaves out.
What it is
A small Windows app for League of Legends. It coaches on Summoner’s Rift and stays silent elsewhere and while spectating. Its HUD is small, click-through and always on top, bottom-right next to the item bar.
While you play, it shows two or three items to buy next, each with a short reason. You decide.
When it answers a threat, a short cue on the HUD names the threat once, and a second small window, the companion, gives the reason in one sentence.
An explainable item model, a sum of named reasons. Not a chatbot or a language model.
Its data is from patch 16.20. On a newer patch it uses the 16.20 data and says so.
The card on the front page is the app’s own render of a scripted test game, not a live one: 4:02, enemy Aatrox. The app drew it at three times the pixels for sharp screens, so it is never enlarged; the game frame under it is a Practice Tool frame from patch 16.19.
The words drifting in the front page’s mist are field names Riot’s Live Client Data API publishes, the data the app reads once a second. The values shown are examples.
What it reads, what it never does
In a game, it reads only Riot’s official, read-only Live Client Data API, once a second: your gold, your items, and the items, kills and levels on the scoreboard. Riot’s developer policies (opens Riot’s developer portal)
By design, it does not read game memory, inject anything or draw inside the game, and it does not touch Vanguard. It does not show hidden information such as enemy gold, positions or timers.
It does not click, type or buy for you. It suggests; you decide.
It is a separate small window on top of the game.
Enemy items reach it about 25 to 40 seconds after they are bought, 70 at most.
Riot has not reviewed or approved it. Riot sets its own rules for third-party tools and can change them.
Not endorsed by Riot Games. Both notices are in the footer.
Reads, sends, stores
Reads: in a game, Riot’s Live Client Data API on your PC, once a second. An optional feature, off by default, also talks to the League client on your PC.
Sends: nothing to the developer. It talks to Discord (the sign-in and the role check, at most once a day), to GitHub (the update check and the update itself; GitHub sees your IP address, like any download) and to Riot’s Data Dragon and CommunityDragon (public item data and icons). No player names, Riot IDs or game data go to any of them. This build has no telemetry.
Stores, on your PC only: its settings, logs, your recent games with names and Riot IDs removed, the post-game receipts built from them, your Discord login (encrypted for your Windows account) and cached item data and icons. Uninstalling keeps this folder; delete it to remove everything.
The numbers
How each number on the front page was measured. The RAM figure is under What it costs your PC.
How often it agrees
The item model’s first choice matched what Emerald+ players bought next 68.3% of the time, and was in its top three 89.5% of the time, on 1,659,465 decisions from 7,618 games it never trained on. Agreement with what Emerald+ players bought, not a win rate.
Threat reactions
A threat reaction is what it does about a threat in your game, such as suggesting anti-heal early against a heavy healer.
2 of 150 judged wrong, graded by AI reviewers (a majority of three, blind), on games no earlier run used. A sample, graded on recorded games, not live play; your own games decide.
“Wrong” means at least two of three AI reviewers, each shown only the game at that second, said the reaction did not fit. The two it got wrong: an anti-heal item against Nasus, who is not a heavy healer, and an armor item against a Yone who was not ahead.
What it costs your PC
About 234 MB of RAM (the private memory of all its processes) and 1.8% of one CPU core while it coaches: the last controlled reading, taken on an earlier build (0.3.3) in three Practice Tool games. The current beta build has not been measured that way yet. It draws nothing inside the game; the HUD is its own small window, always on top. The installer is about 102 MB.
The beta
A closed beta, through the Discord. Free: neither the site nor the app asks for money.
- Join the Discord
- Post in #apply: region, rank, main role, what you play most. Usually approved within a day.
- Get the Beta Tester role, download, sign in with Discord
Your post in #apply answers four questions: your region, your rank, your main role and what you play most. Leave out Riot IDs, links and images: everyone in the server can read the post.
A Warden reads it and replies under it, usually within a day. Then you get the Beta Tester role, and the installer is posted in the testers’ channel. Download it, install it and sign in with Discord in the app.
To check the Beta Tester role, the app asks Discord for your Discord name and your roles in the YATAGARASU server, at most once a day. Discord’s consent screen lists what the app may see; it looks only at your name and your roles, and it does not ask for your email address or your list of servers. The login is stored encrypted on your PC. Apart from the update check and the public item data it downloads, nothing else is sent.
Windows SmartScreen may warn about an unknown publisher: the beta build is not code-signed yet.
If Windows says “Windows protected your PC”, click More info, check that the file name is Yatagarasu-Setup and that you got it from the testers’ channel, then click Run anyway. The Discord announcement gives the installer’s SHA-256; check it first with certutil -hashfile <file> SHA256 in a Command Prompt. If Smart App Control blocks the app, there is no way past it on that PC for now; say so in the Discord.
Who makes it
One developer in Germany. The legal details are in the Impressum.
The name
In the legend, a great crow, Yatagarasu (八咫烏, the eight-span crow), was sent ahead to guide the way through the Kumano mountains: “Make it thy guide through the land.” (Nihongi, Book III, trans. W. G. Aston, 1896). Kumano Hongū Taisha reads the crow’s three legs as heaven, earth and humankind; ours goes ahead in your game.