All stages · Demo 249

ISBN-10

Choice trade / textbook / other. ISBN-10 weights 10 through 1; X is ten. Jev never mods 11. Nine digits need 10.

ChoiceISBN-10 mod-11 in JS

A digit tape. 0306406152 books a trade hardcover. A last-digit flip rejects. Nine digits never pass.

replaykind —isbn10 —

STANDBY

All 4056 stages

Educational stage on jev.page — not the official TypeSafe console. Live calls go to POST https://api.typesafe.ai/v1/systemone from your browser when you paste a key. Without a key, the stage plays a recorded decision shaped like jev-1.13.0. Jev does not write the UI copy.