Skip to main content
Version: 1.4

Linting and formatting

Setting a formatter will override the language server formatting capabilities.

The easiest way is to reference the linter/formatter/code_actions by their names. See the null-ls docs for a full list of builtins with their names.


local formatters = require "lvim.lsp.null-ls.formatters"
formatters.setup {
{ name = "black" },
name = "prettier",
---@usage arguments to pass to the formatter
-- these cannot contain whitespace
-- options such as `--line-width 80` become either `{"--line-width", "80"}` or `{"--line-width=80"}`
args = { "--print-width", "100" },
---@usage only start in these filetypes, by default it will attach to all filetypes it supports
filetypes = { "typescript", "typescriptreact" },

local linters = require "lvim.lsp.null-ls.linters"
linters.setup {
{ name = "flake8" },
name = "shellcheck",
args = { "--severity", "warning" },

local code_actions = require "lvim.lsp.null-ls.code_actions"
code_actions.setup {
name = "proselint",

Installing linters/formatters

You can use :Mason to install most of the supported linters and formatters, if you can't find what you're looking for refer to the each tool's respective manual for installation steps

Lazy-loading the linter/formatter/code_actions setup

By default, all null-ls providers are checked on startup. If you want to avoid that or want to only set up the provider when you opening the associated file-type, then you can use filetype plugins for this purpose.

Let's take python as an example:

  1. create a file called python.lua in the $LUNARVIM_CONFIG_DIR/after/ftplugin folder

  2. add the following snippet

    local linters = require "lvim.lsp.null-ls.linters"
    linters.setup { { command = "flake8", filetypes = { "python" } } }

Formatting on save

  • To enable formatting on save:

    lvim.format_on_save.enabled = true
  • Only enable it for certain filetypes

    lvim.format_on_save.enabled = true
    lvim.format_on_save.pattern = { "*.lua", "*.py" }

Registering custom linters/formatters

LunarVim supports all linters and formatters defined as builtins to null-ls, however there may be occasions where you want to run a linter/formatter that null-ls does not support.

Refer to various docs in the null-ls repo for details on configuring built-in sources and helpers for making builtins.


Do not load registered, custom linters/formatters in your LunarVim config (i.e. in the formatters.setup block). Doing so will raise an error that a builtin source could not be found.

Below is an example registering the htmlbeautifier formatter:

local helpers = require("null-ls.helpers")
local FORMATTING = require("null-ls.methods").internal.FORMATTING
--your custom sources go here
name = "htmlbeautifier",
meta = {
url = "",
description = "A normaliser/beautifier for HTML that also understands embedded Ruby. Ideal for tidying up Rails templates."
method = FORMATTING,
filetypes = { "eruby" },
generator_opts = {
command = "htmlbeautifier",
args = {}, -- put any required arguments in this table
to_stdin = true, -- instructs the command to ingest the file from STDIN (i.e. run the currently open buffer through the linter/formatter)
factory = helpers.formatter_factory,