Table 1.

Website scoring. Per domain a score between 0–1 can be awarded, up to a maximum score of 5 for all domains combined.

Domain	Description of Scoring
Accessibility	Count the amount of clicks 0—>3 mouse clicks to find BRCA information 1—≤3 mouse clicks to find BRCA information Availability of a search bar 0—No search bar 1—Search bar Score calculation Score = $\frac{Sum of the points for the amount of clicks and availibility of a search bar}{2}$
Scope	Number of questions answered/total number of questions JCOs: Questionnaire A1: questions 2–6, excluding 1 and 7. Score out of 23 UKOs: Questionnaire A2: questions 2–6, excluding 1 and 7. Score out of 23 GTPs: Questionnaire A3: questions 2–8. Score out of 26 Number of questions answered/total number of questions per section UKO and JCO: Q2: General BRCA info. Score out of 9 (2a–i) GTP: Q7: BRCA information available. Score out of 7 (7a–g) Score calculation Score = $\frac{Number of questions answered ‘yes’ on Questionnaire A1, A2, or A3}{Total number of questions in corresponding questionnaire}$
Depth	Included questions: BRCA-associated cancers 0—Brief or no information: only breast and/or ovarian 1—In depth: includes prostate, pancreas, and/or melanoma BRCA carrier risk management options 0—Brief or no information: 1–2 options mentioned 1—In depth: all management options (risk-reducing surgery, medication, screening) and/or other options such as lifestyle management Difference of carrier frequency between AJ and non-AJ populations 0—Brief or no information: mentions difference 1—In depth: provides estimates/numbers Explanation of BRCA inheritance 0—Brief or no information: Only mentions inheritance 1—In depth: Mentions 50:50/1 in 2 chance and/or dominant inheritance Increased cancer risks for BRCA carriers 0—Brief or no information: Only brief mention of increased risk of a BRCA-associated cancer or includes general stats for increased risk of a BRCA-associated cancer 1—In depth: Includes statistics or details that differentiate between BRCA1 & BRCA2 risks or includes statistics or details for different BRCA1 & BRCA2 risks for >2 relevant cancers Signposting to further BRCA information, service, and support resources 0—Brief or no information: to less than or equal to 2 resources 1—In depth: to multiple information/support resources Score calculation Score = $\frac{Number of questions with in depth answers on selected depth questions}{6}$
Accuracy *	Included questions: BRCA-associated cancers 0—Inaccurate: any mention of other cancers than the correct ones. 1—Accurate: needs to include breast, ovarian, melanoma, pancreatic or prostate. BRCA carrier risk management options 0—Inaccurate: wrong management options i.e., for example, screening for ovarian cancer 1—Accurate: appropriate chemoprevention, risk-reducing surgery or screening in line with clinical guidelines Carrier frequency/prevalence in AJ population 0—Inaccurate: Other than approximately 1:40 1—Accurate: Approximately 1:40 Carrier frequency/prevalence in general population 0—Inaccurate: anything below 1:400 1—Accurate: 1:250 or anything between 1:200—1:300 Increased cancer risks for BRCA carriers female breast cancer and ovarian cancer [1,2,29] 0—Inaccurate: any of the risks quoted fall outside of ranges from the literature 1—Accurate: all risks quoted fall within the ranges from the literature Increased cancer risks for BRCA carriers male breast cancer, prostate cancer, pancreatic cancer, and melanoma [1,2,29] 0—Inaccurate: any of the risks quoted fall outside of ranges from the literature 1—Accurate: all risks quoted fall within the ranges from the literature Score calculation Score = $\frac{Number of questions with accurate answers on selected accuracy questions}{5}$
Quality	DISCERN score from final question (Q16). Score calculation Score = $\frac{DISCERN score \left(Q16\right)}{5}$

* NA was given to websites without information to assess accuracy.