BackgroundCalcaneal apophysitis is a common condition in childhood. Parents often seek online information for children’s’ health care concerns prior to seeking care. Therefore, we aimed to evaluate the credibility, readability, and accuracy of calcaneal apophysitis advertising on popular websites in three countries.MethodsWe used content analysis of publicly accessible data. This involved identifying the top 50 websites in each country from their hit rates. We used elements of validated tools to audit and determine frequencies relevant to credibility (e.g. publisher), readability (e.g. literacy score) and accuracy (e.g. alignment with evidence). Data were analysed quantitatively and reported against each element.ResultsWebsites were predominantly hosted by private health services (n= 118, 79%). The mean (SD) SMOG (readability) score was 9.3 (4.5). The majority of websites (n= 140, 93%) provided at least one treatment recommendation, and less than 10% (n= 11) of websites advertised treatments fully aligned with evidence. Use of treatment modalities without evidence and with high risk to children were also found including surgery, extracorporeal shock wave therapy and laser.ConclusionsCalcaneal apophysitis online advertising is mostly curated by clinicians. Clinicians should consider revising online advertising to increase understandability and accuracy to reduce health care wastage, risk, and low value care.Supplementary InformationThe online version contains supplementary material available at 10.1186/s13047-023-00637-9.