Source: every tech job listing in a European country on The Stack posted in the window, one count per listing page.
The Stack lists tech jobs that say they offer visa sponsorship, and only those are counted. It is what the listing states, not a check of the employer.
Countries with fewer than 10 visa-sponsored listings in the window are left out of the country table. Roles are matched on job titles.
Recomputed every day. You are welcome to quote these numbers with a link to this page.