# Main Directories in Automattic/harper: A Complete Monorepo Breakdown > Explore the main directories within the Automattic/harper monorepo. Discover its Rust core, WASM bindings, LSP, editor plugins, and Tauri app structure. - Repository: [Automattic/harper](https://github.com/Automattic/harper) - Tags: architecture - Published: 2026-07-26 --- **The Automattic/harper repository is a Rust-based monorepo organized into specialized top-level directories including the core grammar engine, WebAssembly bindings, Language Server Protocol implementation, editor plugins, and a Tauri desktop application.** Harper is a grammar and spell checker built by Automattic that targets both prose and source code comments. The project uses a monorepo structure where each top-level directory represents an independent crate or package, ranging from the core Rust engine to platform-specific integrations. ## Core Grammar Engine and WebAssembly ### harper-core The `harper-core` directory contains the foundational grammar-checking engine that powers all other Harper products. This crate implements the rule engine, tokenizers, and default configuration files. The public API surface is exposed in [`harper-core/src/lib.rs`](https://github.com/Automattic/harper/blob/main/harper-core/src/lib.rs), which defines the primary linting interface used by downstream consumers. ### harper-wasm To enable browser-based usage, `harper-wasm` compiles the core engine to WebAssembly. This directory houses the Rust code that exposes core functionality to JavaScript environments. The entry point at [`harper-wasm/src/lib.rs`](https://github.com/Automattic/harper/blob/main/harper-wasm/src/lib.rs) handles the WASM bindings, allowing the engine to run in web pages and Node.js applications through the [`harper.js`](https://github.com/Automattic/harper/blob/main/harper.js) package. ## Editor Integration and LSP Support ### harper-ls The `harper-ls` directory implements the Language Server Protocol (LSP) used by editors such as VS Code, Neovim, Helix, and Zed. The server binary entry point is located at [`harper-ls/src/main.rs`](https://github.com/Automattic/harper/blob/main/harper-ls/src/main.rs). This component communicates with editors via JSON-RPC to provide real-time diagnostics and code actions without requiring external processes. ### harper-comments Before linting source code, Harper extracts natural language from comments. The `harper-comments` directory contains parsers that handle this extraction across multiple programming languages. The central logic resides in [`harper-comments/src/lib.rs`](https://github.com/Automattic/harper/blob/main/harper-comments/src/lib.rs), which identifies comment boundaries and strips syntax markers so the core engine can analyze the text. ## Natural Language Processing Utilities ### harper-pos-utils Part-of-speech tagging utilities live in `harper-pos-utils`, including a Brill-style tagger and supporting dictionaries. The utility functions are defined in [`harper-pos-utils/src/lib.rs`](https://github.com/Automattic/harper/blob/main/harper-pos-utils/src/lib.rs). ### harper-brill The `harper-brill` directory specifically houses the trained models and runtime for the Brill tagging algorithm used by the POS utilities. ### harper-thesaurus For synonym suggestions and lexical enrichment, `harper-thesaurus` maintains a simple thesaurus database used by the suggestion engine. ## Specialized Domain Linters ### harper-ink The `harper-ink` directory contains a specialized linter for Ink story files, which are used for interactive fiction and narrative scripting. ### harper-jjdescription Version control integration includes `harper-jjdescription`, which parses and validates "JJ" commit descriptions following the project's commit style guidelines. ### harper-git-commit The `harper-git-commit` directory provides a linter for conventional Git commit messages, ensuring formatting standards are met before changes are committed. ### harper-tree-sitter Fast parsing of source files relies on Tree-sitter grammars housed in `harper-tree-sitter`. This directory enables the linter to parse code structure efficiently across supported languages. ## First-Party Integrations and Applications ### packages The `packages` directory is a collection of first-party integrations and UI components: - **chrome-plugin** – Browser extension for Chrome and Firefox - **vscode-plugin** – Visual Studio Code extension packaging - **obsidian-plugin** – Integration for the Obsidian note-taking app - **wordpress-plugin** – WordPress CMS integration - **harper.js** – JavaScript/TypeScript wrapper exported from `harper-wasm` - **harper-editor** – Shared Svelte components used by the website and desktop application - **web** – Public documentation site and demo application source The JavaScript wrapper entry point is located at [`packages/harper.js/src/index.ts`](https://github.com/Automattic/harper/blob/main/packages/harper.js/src/index.ts), while the documentation landing page resides at `packages/web/src/routes/docs/about/+page.md`. ### harper-desktop For offline usage, `harper-desktop` contains a Tauri-based desktop application providing an offline editor, system tray UI, and overlay highlighter. The Tauri backend entry point is [`harper-desktop/src-tauri/src/main.rs`](https://github.com/Automattic/harper/blob/main/harper-desktop/src-tauri/src/main.rs). ## Testing and Infrastructure ### fuzz The `fuzz` directory contains fuzzing harnesses used to stress-test the core engine for crashes and undefined behavior. ### harper-stats Data collection utilities for internal analytics live in `harper-stats`, which records lint-run statistics across various deployment targets. ### Configuration Files Top-level configuration files like [`docker-compose.yml`](https://github.com/Automattic/harper/blob/main/docker-compose.yml) support local development by orchestrating the full stack, while [`Cargo.toml`](https://github.com/Automattic/harper/blob/main/Cargo.toml) and [`pnpm-workspace.yaml`](https://github.com/Automattic/harper/blob/main/pnpm-workspace.yaml) define the Rust and JavaScript workspace boundaries. ## Key Entry Points When navigating the Harper source code, these files serve as the primary interfaces: - [`harper-core/src/lib.rs`](https://github.com/Automattic/harper/blob/main/harper-core/src/lib.rs) – Public API of the core engine - [`harper-wasm/src/lib.rs`](https://github.com/Automattic/harper/blob/main/harper-wasm/src/lib.rs) – JavaScript exposure via WASM - [`harper-ls/src/main.rs`](https://github.com/Automattic/harper/blob/main/harper-ls/src/main.rs) – LSP server startup - [`harper-comments/src/lib.rs`](https://github.com/Automattic/harper/blob/main/harper-comments/src/lib.rs) – Comment extraction logic - [`packages/harper.js/src/index.ts`](https://github.com/Automattic/harper/blob/main/packages/harper.js/src/index.ts) – JavaScript wrapper - [`harper-desktop/src-tauri/src/main.rs`](https://github.com/Automattic/harper/blob/main/harper-desktop/src-tauri/src/main.rs) – Desktop binary entry - `justfile` – Central task runner for builds ## Building and Testing Components Developers interact with specific directories using standard Rust tooling: ```bash # Build the core engine cargo build -p harper-core # Compile WebAssembly for browser usage cd harper-wasm && wasm-pack build --release # Run the Language Server locally cd harper-ls && cargo run --release # Test comment extraction cargo test -p harper-comments --lib # Launch desktop app (requires Tauri CLI) cd harper-desktop && just dev-desktop ``` ## Summary - **harper-core** provides the foundational grammar engine at [`harper-core/src/lib.rs`](https://github.com/Automattic/harper/blob/main/harper-core/src/lib.rs) - **harper-wasm** enables browser execution through WebAssembly bindings - **harper-ls** implements the Language Server Protocol for editor integration - **harper-comments** extracts translatable text from source code comments - **packages** contains first-party integrations including VS Code, Chrome, Obsidian, and WordPress plugins - **harper-desktop** delivers a Tauri-based offline application - **fuzz** and **harper-stats** support quality assurance and analytics ## Frequently Asked Questions ### What is the purpose of the harper-core directory? The `harper-core` directory houses the Rust-based grammar-checking engine that tokenizes input and applies linting rules. It serves as the foundation for all other Harper products, with its public API defined in [`harper-core/src/lib.rs`](https://github.com/Automattic/harper/blob/main/harper-core/src/lib.rs). ### How does harper-ls differ from the packages in the packages directory? The `harper-ls` directory implements the Language Server Protocol server that provides diagnostics to any LSP-compatible editor, while the `packages` directory contains specific UI implementations and wrappers like the VS Code extension (`packages/vscode-plugin`) and JavaScript library ([`packages/harper.js`](https://github.com/Automattic/harper/blob/main/packages/harper.js)). ### Where is the WebAssembly compilation logic located? WebAssembly bindings are defined in [`harper-wasm/src/lib.rs`](https://github.com/Automattic/harper/blob/main/harper-wasm/src/lib.rs) within the `harper-wasm` directory. This crate compiles the core engine to WASM so it can be consumed by the [`harper.js`](https://github.com/Automattic/harper/blob/main/harper.js) package and web-based interfaces. ### Which directory should I modify to add support for a new programming language's comments? To add support for extracting comments from a new programming language, modify the `harper-comments` directory, specifically the parsers in [`harper-comments/src/lib.rs`](https://github.com/Automattic/harper/blob/main/harper-comments/src/lib.rs) that identify comment syntax across different file types.