The Internet is transforming into the main source of information. Standards are being developed so that people with different types of disabilities are not to feel excluded. Tools based on certain standards automate tasks, but they are also important to work correctly. The study consisted of checking the pages with selected tools discussed in the literature dealing with website accessibility. The validators are identically configured each time the website verifies compliance with the WCAG 2.1 standard. The number of errors detected per page varies significantly when using individual tools. The error rate calculated for the number of all HTML elements of the page ranges between less than 1% and 80%. It is not possible to unambiguously select the worst service on the basis of analyzing all results obtained, it can be a different service for each tool. The tools automate the activities of verifying availability. Each of the validators tested found errors, some of the same. The best solution is not to rely on just one tool, because the results obtained can relate to completely different elements of the page. It all depends on the care of the creators in the preparation of the tool and their care for compliance with standards.