Where Are the Source Files Located in the Automattic/Harper Repository?

The Automattic/harper source files are organized in a monorepo structure with top-level directories for Rust crates and npm workspace packages under packages/.

The Harper spell- and grammar-checking ecosystem is developed as a single Git repository that bundles multiple components—ranging from a Rust core engine to browser extensions and a desktop application. Understanding where the source files live in the Automattic/harper repository helps contributors navigate the codebase, import the right modules, and build specific components.

Rust Components: Top-Level Crate Directories

Harper's foundational logic resides in several Rust crates located at the repository root. Each crate is a standard Cargo project with its own Cargo.toml and src/ directory.

harper-core: The Grammar-Checking Engine

The harper-core directory contains the core linting engine written in Rust. This is the heart of Harper—implementing tokenization, rule evaluation, and diagnostic generation.

• Primary source: harper-core/src/
• Library entry point: harper-core/src/lib.rs
• Key exports: Linter struct and lint() method for programmatic use

Downstream Rust crates reference harper-core via path dependency:

[dependencies]
harper-core = { path = "../harper-core" }

use harper_core::Linter;

fn main() {
    let mut linter = Linter::new_default();
    let text = "This is a smaple sentence.";
    let result = linter.lint(text);
    println!("{:?}", result);
}

harper-ls: Language Server Protocol Implementation

Editor integrations rely on harper-ls, the LSP implementation. Located at harper-ls/, this crate exposes Harper's diagnostics through the Language Server Protocol used by VS Code, Neovim, and other editors.

• Executable entry point: harper-ls/src/main.rs
• Protocol handlers: Defined in harper-ls/src/

harper-wasm: WebAssembly Bindings

The harper-wasm crate at harper-wasm/ compiles the core engine to WebAssembly. This enables browser and Node.js usage via the harper.js package.

• WASM entry point: harper-wasm/src/lib.rs
• Build output: Consumed by packages/harper.js/

harper-comments and harper-tex: Specialized Parsers

Two additional Rust crates provide domain-specific functionality:

• harper-comments (harper-comments/): Extracts and lints comments from source code files
• harper-tex (harper-tex/): LaTeX-specific processing utilities

Both follow the standard src/lib.rs pattern for library crates.

harper-desktop: Tauri-Based Desktop Application

The harper-desktop directory contains a hybrid Rust/SvelteKit application:

Layer	Location	Entry Point
Rust backend	harper-desktop/src-tauri/	harper-desktop/src-tauri/src/main.rs
SvelteKit frontend	harper-desktop/src/	harper-desktop/src/routes/+page.svelte

Run the development server from the repository root:

just dev-desktop

JavaScript/TypeScript Components: The packages/ Directory

All npm-managed source files in Automattic/harper live under the packages/ directory, configured as a pnpm workspace via pnpm-workspace.yaml at the repository root.

harper.js: The Public JavaScript API

packages/harper.js/ bundles the WASM module and provides a TypeScript-friendly interface:

• Entry point: packages/harper.js/src/index.ts
• Primary class: LocalLinter for in-process linting

npm i file:./packages/harper.js

import { LocalLinter } from 'harper.js';

(async () => {
  const linter = await LocalLinter.create();
  const diagnostics = await linter.lint('This is a smaple sentence.');
  console.log(diagnostics);
})();

Lint Framework and Editor Components

Two shared packages support multiple Harper UIs:

• packages/lint-framework/: UI-agnostic lint utilities and types (src/index.ts)
• packages/harper-editor/: Reusable Svelte components (src/lib/Editor.svelte)

Web Site and Documentation

The packages/web/ directory contains a SvelteKit site powering writewithharper.com:

• Documentation content: packages/web/src/routes/docs/about/+page.md

Browser and Editor Extensions

Multiple plugin implementations share the packages/ parent:

Extension	Location	Activation File
Chrome	packages/chrome-plugin/	src/background.ts
Firefox	packages/firefox-plugin/	src/background.ts
VS Code	packages/vscode-plugin/	src/extension.ts
Obsidian	packages/obsidian-plugin/	src/main.ts
WordPress	packages/wordpress-plugin/	src/plugin.php

Build Orchestration Files

The Automattic/harper repository uses two workspace systems to coordinate its multi-language structure:

• Rust: Root Cargo.toml with workspace members pointing to each top-level crate directory
• JavaScript: pnpm-workspace.yaml declaring packages/* as workspace packages

Summary

• Rust source files live in top-level directories: harper-core/, harper-ls/, harper-wasm/, harper-comments/, harper-tex/, and harper-desktop/
• JavaScript/TypeScript source files are grouped under packages/, including harper.js, browser extensions, and Svelte components
• Key entry points include harper-core/src/lib.rs for the engine and packages/harper.js/src/index.ts for the JS API
• Documentation source is located in packages/web/src/routes/docs/

Frequently Asked Questions

What is the main entry point for using Harper as a Rust library?

The main entry point is harper-core/src/lib.rs. This file exports the Linter struct and related types that power all Harper linting functionality. Import harper_core in your Cargo.toml to use it.

How do I find the source for the VS Code extension?

The VS Code extension source is located at packages/vscode-plugin/. The extension activates through packages/vscode-plugin/src/extension.ts, which launches the harper-ls language server as a separate process.

Where is the WebAssembly compilation step defined?

The Rust-to-WASM compilation lives in harper-wasm/src/lib.rs. This crate uses wasm-bindgen to generate JavaScript bindings. The resulting WASM binary is packaged by packages/harper.js/ for npm distribution.

Can I build just one component without the entire monorepo?

Yes. Each Rust crate is a standard Cargo project that builds independently with cargo build. JavaScript packages in packages/ can be built individually with pnpm --filter <package-name> build, though some depend on the WASM output from harper-wasm.

{
  "mcpServers": {
    "instagit": {
      "command": "npx",
      "args": ["-y", "instagit@latest"]
    }
  }
}