Document and Entity Information Document - shares	9 Months Ended
	Sep. 26, 2020	Oct. 14, 2020
Cover [Abstract]
Entity Registrant Name	ONTO INNOVATION INC.
Trading Symbol	ONTO
Entity Central Index Key	0000704532
Current Fiscal Year End Date	--12-28
Entity Filer Category	Large Accelerated Filer
Document Type	10-Q
Document Period End Date	Sep. 26, 2020
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q3
Document Quarterly Report	true
Document Transition Report	false
Entity Interactive Data Current	Yes
Amendment Flag	false
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Current Reporting Status	Yes
Entity Shell Company	false
Title of 12(b) Security	Common Stock, $0.001 par value per share
Security Exchange Name	NYSE
Entity Common Stock, Shares Outstanding		48,831,308
Entity File Number	001-39110
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	94-2276314
Entity Address, Address Line One	16 Jonspin Road
Entity Address, City or Town	Wilmington
Entity Address, State or Province	MA
Entity Address, Postal Zip Code	01887
City Area Code	978
Local Phone Number	253-6200