The checks use official published sources: the planning data platform, Historic England, Cadw and Historic Environment Scotland, the Environment Agency, Natural Resources Wales and SEPA, and each council’s own data where it publishes it. Planning application history comes from PlanIt, a private aggregator. The full list, with licences, is on the sources and licences page.
It is a screening tool. It is not an official local authority search, not a CON29 or an LLC1, and not professional advice. Some councils do not publish every dataset, so where it matters, ask the council. Northern Ireland is not covered.