Structured Data Testing Tool retired
Google retired its Structured Data Testing Tool in favour of the Rich Results Test and handed the generic validator to Schema.org.
What changed
Google announced in July 2020 that the Structured Data Testing Tool would be deprecated once the Rich Results Test left beta, because the older tool validated markup generically rather than showing what Google would actually use. The generic validation function was migrated to the Schema.org-hosted validator, and the Google-hosted tool was withdrawn during 2021. Practitioners lost a single tool that both validated syntax and previewed eligibility, and now use the two separately. Only month-level precision is documented for both dates.
Timing
Announced on 1 July 2020, with rollout beginning 1 July 2021. No completion date was announced. Rankings typically remain unstable for the whole rollout window, so measurements taken inside it are not a reliable read on the outcome.