Horses suffering from joint degeneration (osteoarthritis) often suffer pain and lameness that affect their wellbeing and welfare. Owners or caregivers observe and interact with their horses the most, but as pain and disability can vary over time, it would be valuable to have a tool to help them monitor their horses’ level of osteoarthritis pain. To this end, researchers designed a questionnaire. Items to be included were determined based on the scientific literature about pain expression and behaviour in horses, as well as input from discussions with owners, caregivers, and veterinary experts. The researchers then tested the tool for ease of use and interpretation in 25 owners/caretakers of arthritic horses. Of these, 88% found the tool useful, and 84% found it easy to use. The tool took less than 5 min to complete, and readability tests showed it could be completed reliably by people with English language reading skills comparable to those with a 6th or 7th grade education. The resulting tool is undergoing further reliability testing in a larger population of owners/caretakers of arthritic and healthy horses before it can be introduced in practice.