v3.25.2
Cover - shares
6 Months Ended
Jun. 30, 2025
Jul. 28, 2025
Cover [Abstract]    
Document Type 10-Q  
Document Quarterly Report true  
Document Period End Date Jun. 30, 2025  
Document Transition Report false  
Entity File Number 001-38984  
Entity Registrant Name CASTLE BIOSCIENCES, INC.  
Entity Incorporation, State or Country Code DE  
Entity Tax Identification Number 77-0701774  
Entity Address, Address Line One 505 S. Friendswood Drive  
Entity Address, Address Line Two Suite 401  
Entity Address, City or Town Friendswood  
Entity Address, State or Province TX  
Entity Address, Postal Zip Code 77546  
City Area Code 866  
Local Phone Number 788-9007  
Title of 12(b) Security Common Stock, $0.001 par value per share  
Trading Symbol CSTL  
Security Exchange Name NASDAQ  
Entity Current Reporting Status Yes  
Entity Interactive Data Current Yes  
Entity Filer Category Accelerated Filer  
Entity Small Business false  
Entity Emerging Growth Company false  
Entity Shell Company false  
Entity Common Stock, Shares Outstanding   29,008,281
Entity Central Index Key 0001447362  
Current Fiscal Year End Date --12-31  
Document Fiscal Year Focus 2025  
Document Fiscal Period Focus Q2  
Amendment Flag false