Detect downtime before your customers do. Juha will constantly use your site or service, and will test that the service continues to be and running from the end user perspective. Depending on the exact nature of the site or service, Juha will browse to different pages or parts of the system, and will issue alerts if some parts of the system are either down or are returning errors.
Detect broken links, erroneous settings, typographical errors, etc. While testing the service, Juha will also observe the contents of the data it encounters, and ensures that to the best of its knowledge, the data is correct and functional. Practically this can mean eg. verifying that all links on the site or application are working and therefore correctly spelled; that external links are pointing to real and functioning services; that social media integration is correct and functional, and pointing to valid social media accounts; and many other similar validations.
Make sure your code is correct, unchanged and safe. Juha can also read and analyze application code that it encounters, whether in human readable or machine readable format. With this skill set, Juha can also verify that the code running your service is valid and functional, and that it does not contain known or obvious bugs or security vulnerabilities. Over time Juha can also learn the structure and state or your code, and will be able to detect and provide you with alerts in cases where the code would be unexpectedly changed.
Monitor your services also under the hood. Juha also has the ability to utilize remote connections via SSH or similar means, and to perform administrative tasks directly on servers on the cloud or in premises, provided that it will be provided with necessary credentials or other access rights. With that kind of connectivity in place, Juha will be able to also monitor service health on the system level, monitoring disk space, system load, memory usage, processes, and other similar, possibly even application specific, measurables.