| Cover | Aug. 13, 2024 |
| Document Type | 8-K |
| Amendment Flag | false |
| Document Period End Date | Aug. 13, 2024 |
| Entity File Number | 001-41003 |
| Entity Registrant Name | ONYX ACQUISITION CO. I |
| Entity Central Index Key | 0001849548 |
| Entity Tax Identification Number | 98-1584432 |
| Entity Incorporation, State or Country Code | E9 |
| Entity Address, Address Line One | 104 5th Avenue |
| Entity Address, City or Town | New York |
| Entity Address, State or Province | NY |
| Entity Address, Postal Zip Code | 10011 |
| City Area Code | 212 |
| Local Phone Number | 974-2844 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Entity Emerging Growth Company | false |
| Units, each consisting of one Class A Ordinary Share, $0.0001 par value, and one-half of one redeemable warrant | |
| Title of 12(b) Security | Units, each consisting of one Class A Ordinary Share, $0.0001 par value, and one-half of one redeemable warrant |
| Trading Symbol | ONYXU |
| Security Exchange Name | NASDAQ |
| Class A Ordinary Shares included as part of the units | |
| Title of 12(b) Security | Class A Ordinary Shares included as part of the units |
| Trading Symbol | ONYX |
| Security Exchange Name | NASDAQ |
| Redeemable warrants included as part of the units, each whole warrant exercisable for one Class A Ordinary Share at an exercise price of $11.50 | |
| Title of 12(b) Security | Redeemable warrants included as part of the units, each whole warrant exercisable for one Class A Ordinary Share at an exercise price of $11.50 |
| Trading Symbol | ONYXW |
| Security Exchange Name | NASDAQ |
