XP (experience points) is Tarc's core progress metric — a running total of how much lesson content you've correctly completed.
You earn XP by answering correctly during lessons and quizzes, and by completing daily quests and login rewards. XP boosts purchased from the shop (25% or 50% for a limited time) multiply the amount earned during that window.
Tarc tracks two separate XP figures: your lifetime total XP (shown on your profile and used for the leaderboard and XP-milestone achievements), and today's XP (reset daily, used for the daily goal ring on the Learn tab).
XP doesn't gate access to lessons or levels — course progression is based on completing lessons, not accumulating a specific XP total. It's a progress and motivation metric, not a currency (that's what gems are for).
No — course progression depends on completing lessons in order, not on reaching a specific XP total. XP is a progress and ranking metric, not a gate.
Total XP is your lifetime cumulative amount, used for your profile and the leaderboard; today's XP resets daily and is used only for the daily goal ring.
Yes — a purchased boost (25% or 50%) increases the XP earned from lessons for its active duration.