| Document And Entity Information | Mar. 27, 2024 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Amendment Flag | false |
| Document Period End Date | Mar. 27, 2024 |
| Entity Registrant Name | Metagenomi, Inc. |
| Entity Central Index Key | 0001785279 |
| Entity Emerging Growth Company | true |
| Entity File Number | 001-41949 |
| Entity Incorporation, State or Country Code | DE |
| Entity Tax Identification Number | 81-3909017 |
| Entity Address, Address Line One | 5959 Horton Street |
| Entity Address, Address Line Two | 7th Floor |
| Entity Address, City or Town | Emeryville |
| Entity Address, State or Province | CA |
| Entity Address, Postal Zip Code | 94608 |
| City Area Code | (510) |
| Local Phone Number | 871-4880 |
| Entity Information, Former Legal or Registered Name | Not Applicable |
| 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 | MGX |
| Security Exchange Name | NASDAQ |
