| Document And Entity Information | Jan. 07, 2021 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Amendment Flag | false |
| Document Period End Date | Jan. 7, 2021 |
| Entity Registrant Name | ONTO INNOVATION INC. |
| Entity Central Index Key | 0000704532 |
| Entity Emerging Growth Company | false |
| 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 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(b) Security | Common Stock, $0.001 par value per share |
| Trading Symbol | ONTO |
| Security Exchange Name | NYSE |
