| Document And Entity Information | Jul. 16, 2024 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Amendment Flag | false |
| Document Period End Date | Jul. 16, 2024 |
| Entity Registrant Name | RAPT Therapeutics, Inc. |
| Entity Central Index Key | 0001673772 |
| Entity Emerging Growth Company | true |
| Entity File Number | 001-38997 |
| Entity Incorporation, State or Country Code | DE |
| Entity Tax Identification Number | 47-3313701 |
| Entity Address, Address Line One | 561 Eccles Avenue |
| Entity Address, City or Town | South San Francisco |
| Entity Address, State or Province | CA |
| Entity Address, Postal Zip Code | 94080 |
| City Area Code | (650) |
| Local Phone Number | 489-9000 |
| Entity Information, Former Legal or Registered Name | N/A |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Entity Ex Transition Period | false |
| Title of 12(b) Security | Common Stock, $0.0001 par value per share |
| Trading Symbol | RAPT |
| Security Exchange Name | NASDAQ |
