Language Check

A fast, extensible grammar and style checker for Markdown, HTML, LaTeX, and more. Powered by a Rust core with tree-sitter parsing — checks run locally with no external service required.

Features

Instant local checking — built-in Harper engine gives sub-second feedback with no network dependency
Multi-engine support — optionally add LanguageTool for deep grammar analysis, external tools like Vale, or custom WASM plugins
Smart prose extraction — tree-sitter parsing skips code blocks, math environments, and markup so you only get relevant diagnostics
SpeedFix panel — keyboard-driven batch review (Alt+F): press 1–9 for suggestions, a to add to dictionary, i to ignore, Space to skip
Inline suggestions — inlay hints, ghost text completions, and quick-fix code actions
Prose insights — word count, sentence count, and readability index in the status bar
Inspector — debug view showing AST structure, extraction ranges, and check latency

Supported Languages

Markdown, HTML, LaTeX, Typst, reStructuredText, BibTeX, Org-mode, MDX, XHTML, Sweave, and Forester — plus any language with a Schema Language Specification (SLS) file.

Getting Started

Install the extension
Open a supported file — checking starts automatically
Press Alt+F to open SpeedFix for fast batch fixes

No configuration needed for basic usage. The local Harper engine works out of the box.

Configuration

Create a .languagecheck.yaml in your workspace root for advanced settings:

engines:
  harper: true
  languagetool: true
  languagetool_url: "http://localhost:8010"

rules:
  spelling.typo:
    severity: warning
  grammar.article:
    severity: off

auto_fix:
  - find: "teh"
    replace: "the"

Or run Language Check: Config Init from the command palette to generate a default config.

Extension Settings

Setting	Default	Description
`languageCheck.check.trigger`	`onChange`	Check on every change or only on save
`languageCheck.core.channel`	`stable`	Core binary release channel (stable/canary/dev)
`languageCheck.core.binaryPath`	—	Path to a custom core binary
`languageCheck.dictionaries.bundled`	`true`	Use bundled dictionaries
`languageCheck.dictionaries.paths`	`[]`	Additional dictionary file paths
`languageCheck.performance.highPerformanceMode`	`false`	Optimize for large files
`languageCheck.workspace.indexOnOpen`	`false`	Index workspace files on open
`languageCheck.trace.enable`	`false`	Enable protocol tracing for debugging

Commands

Command	Description
`Language Check: Check Document`	Run checks on the current file
`Language Check: Check Workspace`	Check all supported files in the workspace
`Language Check: Open SpeedFix`	Open the keyboard-driven fix panel (`Alt+F`)
`Language Check: Select Language`	Override the detected language for the current file
`Language Check: Open Inspector`	Open the debug inspector panel
`Language Check: Switch Core`	Switch between core binary channels
`Language Check: Skip LaTeX Environment`	Add a LaTeX environment to the skip list
`Language Check: Skip LaTeX Command`	Add a LaTeX command to the skip list

CLI

Language Check also ships as a standalone CLI:

# Install via Homebrew
brew install KaiErikNiermann/lang-check/lang-check

# Or via cargo
cargo install lang-check

# Check files
language-check check README.md
language-check fix docs/
language-check list-rules

License

MIT