Objective: To evaluate the quality, understandability, actionability and readability of English-language Internet-based resources about autism spectrum disorder. Design: Cross-sectional observational study evaluating the quality, accountability, understandability, actionability and readability of English-language Internet-based resources related to autism spectrum disorder. Setting: The study was conducted using publicly available webpages accessed through Google and Yahoo search engines, identified based on search terms relevant to autism spectrum disorder, as determined by Google Trends and SEMRUSH data. Data collection occurred in March 2023. Method: Google Trends was used to identify the terms most likely searched by consumers when looking for information related to autism. The HON, URAC, JAMA benchmark criteria and the DISCERN instrument were used to evaluate webpage quality and accountability. We used the PEMAT-P to evaluate webpage understandability and actionability. The Flesch-Kincaid Grade Level, Flesch Reading Ease, Gunning Fog Index and the Simple Measure of Gobbledygook were used to evaluate webpage readability. Results: In total, 103 webpages were analysed. Nine webpages displayed the HON seal. Six webpages met all core JAMA standards, 23 met three core standards, 35 met one core standard and six met none of the core standards. DISCERN scores ranged from 16 to 53 (Mdn = 33.00; IQR = 41.00-27.00). PEMAT-P understandability and actionability scores were 8.52 ± 2.10 and 1.30 ± 1.04, respectively. Readability scores, on average, exceeded the recommended grade reading levels (FRE = 27.00 ± 12.19, F-KGL = 15.20 ± 2.32, FOG = 12.70 ± 2.09 and SMOG = 15.70 ± 1.78). Conclusion: Most webpages did not meet the criteria for quality, understandability, actionability and readability. The developers of websites aimed at autistic persons and their care partners should consider the findings of this study when developing patient education materials. Doing so will facilitate improved communication with healthcare consumers, resulting in improved outcomes.