The first thing to do is not to highlight anything. Open Settings and find the visibility control for highlights — and the separate one under AI Clone & Hatch — before you mark a single passage. Which way those switches start is genuinely unclear from outside Glasp (see Privacy below), and they decide whether your reading is public.
Free to use with a sign-up and no card. The thing you would pay for here is privacy, not capability: Pro — a monthly plan, cheaper if you pay for a year, with a student discount — is what adds unlimited private highlights. Whether a free account gets any private highlights at all is not something Glasp's own pages settle either way.
Highlighting itself is unlimited and unmetered, but the AI features are rationed on the free plan: a small monthly allowance of chat credits (the platform's unit of spend — each thing you ask costs some), a daily cap on basic YouTube summaries, and a cap on PDF uploads. Chatting with a PDF is metered too, on a separate allowance Glasp's pages do not describe consistently, so check the current limits in the app rather than planning around fixed numbers.
It is a browser add-on, so it lives in a browser: Chrome, Safari, Edge and Firefox have published versions, and Brave and Opera install the Chrome one. Phone browsers cannot run add-ons at all, which is why there are separate iPhone, iPad and Android apps with their own built-in reader.
You are not locked in. Glasp states plainly that export is not a paid feature — "your highlights are yours, and we would rather you could leave than feel stuck."