v3.26.1
Cover - USD ($)
 12 Months Ended
Dec. 31, 2025
Mar. 01, 2026
Jun. 30, 2025
Cover [Abstract]      
Document Type 10-K    
Document Annual Report true    
Document Period End Date Dec. 31, 2025    
Current Fiscal Year End Date --12-31    
Document Transition Report false    
Entity File Number 001-43105    
Entity Registrant Name SpyGlass Pharma, Inc.    
Entity Incorporation, State or Country Code DE    
Entity Tax Identification Number 83-3044245    
Entity Address, Address Line One 27061 Aliso Creek Rd.    
Entity Address, Address Line Two Suite 100    
Entity Address, City or Town Aliso Viejo    
Entity Address, State or Province CA    
Entity Address, Postal Zip Code 92656    
City Area Code 949    
Local Phone Number 284-6904    
Title of 12(b) Security Common Stock, par value $0.00001 per share    
Trading Symbol SGP    
Security Exchange Name NASDAQ    
Entity Well-known Seasoned Issuer No    
Entity Voluntary Filers No    
Entity Current Reporting Status No    
Entity Interactive Data Current Yes    
Entity Filer Category Non-accelerated Filer    
Entity Small Business true    
Entity Emerging Growth Company true    
Entity Ex Transition Period false    
ICFR Auditor Attestation Flag false    
Document Financial Statement Error Correction [Flag] false    
Entity Shell Company false    
Entity Common Stock, Shares Outstanding   33,426,557  
Documents Incorporated by Reference
None
    
Central Index Key 0001778922    
Amendment Flag false    
Document Fiscal Year Focus 2025    
Document Fiscal Period Focus FY    
Entity Public Float     $ 0