automattic/harper is an English grammar checker that runs inside the device. The default configuration checks text locally without sending content to an external server, and the latest public release is v2.13.0. It is an open-source project implemented in Rust, and the repository was created on October 22, 2023.
The README says Harper checks documents in milliseconds and uses less than 1/50 of the memory that LanguageTool uses. That figure is a comparison the project presents itself, not an independently verified result. It advertises fully private operation and can also be loaded as WebAssembly, so it can run in a browser or in a personal tool. The license is Apache-2.0, and the repository has collected 16900 stars.
Still, the only language supported today is English. Covering other languages requires extending the core functionality, and the README states that contributions in that direction are welcome. That v2.13.0 is the latest release is confirmed, but the changelog is not in the given material.
The evaluation record leaves only a momentum score of 8.1 out of 10, while the freshness, technology and quality scores are empty. There is also no material comparing grammar-checking accuracy, so the advantages that can be confirmed now are limited to checking speed and private handling. It is worth trying first as a tool for writing documents, but it is too early to judge whether to adopt it across a team.