languagetool.nvim

A Neovim plugin for grammar and spell checking using LanguageTool.

Requirements

• Neovim 0.9+
• A running LanguageTool server (local or remote)
• curl

Installation

Using lazy.nvim:

{
  "auyer/languagetool.nvim",
  opts = {
    server_url = "http://localhost:8081",
    language = "en-US",
  },
  keys = {
    { "<leader>lc", "<cmd>LTCheck<cr>", desc = "Check line" },
    { "<leader>lc", ":LTCheck<cr>", mode = "v", desc = "Check selection" },
    { "<leader>lb", "<cmd>LTCheckBuffer<cr>", desc = "Check buffer" },
    { "<leader>lf", "<cmd>LTFix<cr>", desc = "Show fixes" },
    { "<leader>la", "<cmd>LTCodeAction<cr>", desc = "Code action" },
    { "<leader>lx", "<cmd>LTClear<cr>", desc = "Clear diagnostics" },
  },
}

Configuration

require("languagetool").setup({
  -- LanguageTool server URL
  server_url = "http://localhost:8081",
  -- A language code like en-US, de-DE, fr, auto ...
  language = "auto",
  -- Optional motherTongue config
  motherTongue = nil,
  -- "default" and "picky" available
  level = "default",
  -- Show top N suggestions in diagnostic messages
  suggestions_in_diagnostic = 3,
  -- Enable virtual text showing top suggestion (set false to disable)
  virtual_text = true,
  -- Max chars per API call (under 20K free limit; large texts are chunked)
  max_chunk_chars = 19000,
  -- Max concurrent curl calls when checking large files
  max_concurrent_calls = 4,
  -- Optional API credentials
  username = nil,
  api_key = nil,
  -- Severity mapping for different issue types
  severity = {
    typographical = vim.diagnostic.severity.HINT,
    grammar = vim.diagnostic.severity.WARN,
    misspelling = vim.diagnostic.severity.ERROR,
    style = vim.diagnostic.severity.INFO,
    default = vim.diagnostic.severity.WARN,
  },
})

Commands

Command	Description
:LTCheck	Check current line
:'<,'>LTCheck	Check visual selection
:LTCheckBuffer	Check entire buffer
:LTFix	Show available fixes at cursor
:LTCodeAction	LSP-like code action — show fixes or fall through to native LSP code actions
:LTClear	Clear all LanguageTool diagnostics

Features

• Async checking (non-blocking)
• Integrates with Neovim's built-in diagnostics (vim.diagnostic)
• Diagnostic messages include top suggestions
• Virtual text shows the top suggestion inline (can be disabled)
• LSP-like code actions (:LTCodeAction) with fallback to native LSP
• Fix picker uses vim.ui.select (works with Telescope, fzf-lua, snacks.nvim, etc.)
• Configurable severity levels per issue type

Running LanguageTool Server

You can run LanguageTool locally using Docker:

docker run --rm -p 8081:8010 erikvl87/languagetool

Or download and run the standalone server.

Testing

Run the test suite against a local LanguageTool server:

# 1. Generate API response fixtures (requires a running LT server)
mkdir -p tests/fixtures
printf 'since april\nteste text\nthis is an example with on error.\n' > tests/fixtures/sample.txt
printf 'since april\n' > tests/fixtures/single_line.txt

curl -sS -X POST -d 'language=en-US' -d 'level=picky' \
  --data-urlencode 'text@tests/fixtures/sample.txt' \
  'http://<language-tool-url>/v2/check' > tests/fixtures/sample.json

curl -sS -X POST -d 'language=en-US' -d 'level=picky' \
  --data-urlencode 'text@tests/fixtures/single_line.txt' \
  'http://<language-tool-url>/v2/check' > tests/fixtures/single_line.json

# 2. Run the tests
nvim --headless --cmd "set rtp+=." -c "luafile tests/test_plugin.lua"

Tests use mock API responses — no server needed after fixture generation.

License

GPL V3