| Document and Entity Information | May 12, 2022 |
| Cover [Abstract] | |
| Amendment Flag | false |
| Entity Central Index Key | 0001759138 |
| Document Type | 8-K |
| Document Period End Date | May 12, 2022 |
| Entity Registrant Name | CABALETTA BIO, INC. |
| Entity Incorporation State Country Code | DE |
| Entity File Number | 001-39103 |
| Entity Tax Identification Number | 82-1685768 |
| Entity Address, Address Line One | 2929 Arch Street |
| Entity Address, Address Line Two | Suite 600 |
| Entity Address, City or Town | Philadelphia |
| Entity Address, State or Province | PA |
| Entity Address, Postal Zip Code | 19104 |
| City Area Code | (267) |
| Local Phone Number | 759-3100 |
| Written Communications | false |
| Soliciting Material | false |
| Pre Commencement Tender Offer | false |
| Pre Commencement Issuer Tender Offer | false |
| Security 12b Title | Common Stock, par value $0.00001 per share |
| Trading Symbol | CABA |
| Security Exchange Name | NASDAQ |
| Entity Emerging Growth Company | true |
| Entity Ex Transition Period | false |
