Free public beta until December 4, 2026: every course is open, no card needed. After that, the first chapter of each course stays free and full access is a one-time $39 ($19 for up to 100 founding members chosen for helpful feedback). Your progress is kept. How the beta works

JSON

A text format of objects, arrays, strings, numbers, true/false and null.

RFC 8259's data format: objects of double-quoted names and values, arrays, strings with backslash escapes, numbers, booleans and null; no comments, no trailing commas, no date type.