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8 hours ago


Lightweight yet powerful formatter plugin for Neovim


  • Neovim 0.8+


  • Preserves extmarks and folds - Most formatters replace the entire buffer, which clobbers extmarks and folds, and can cause the viewport and cursor to jump unexpectedly. Conform calculates minimal diffs and applies them using the built-in LSP format utilities.
  • Fixes bad-behaving LSP formatters - Some LSP servers are lazy and simply replace the entire buffer, leading to the problems mentioned above. Conform hooks into the LSP handler and turns these responses into proper piecewise changes.
  • Enables range formatting for all formatters - Since conform calculates minimal diffs, it can perform range formatting even if the underlying formatter doesn't support it.
  • Simple API - Conform exposes a simple, imperative API modeled after vim.lsp.buf.format().


conform.nvim supports all the usual plugin managers

  opts = {},
    use {
      config = function() require('conform').setup() end
require "paq" {
Plug 'stevearc/conform.nvim'
call dein#add('stevearc/conform.nvim')
git clone --depth=1 ~/.vim/bundle/
git clone --depth=1 \


At a minimum, you will need to set up some formatters by filetype

    formatters_by_ft = {
        lua = { "stylua" },
        -- Conform will run multiple formatters sequentially
        python = { "isort", "black" },
        -- Use a sub-list to run only the first available formatter
        javascript = { { "prettierd", "prettier" } },

Then you can use conform.format() just like you would vim.lsp.buf.format(). For example, to format on save:

vim.api.nvim_create_autocmd("BufWritePre", {
    pattern = "*",
    callback = function(args)
        require("conform").format({ bufnr = args.buf })

As a shortcut, conform will optionally set up this format-on-save autocmd for you

    format_on_save = {
        -- These options will be passed to conform.format()
        timeout_ms = 500,
        lsp_fallback = true,

See conform.format() for more details about the parameters.

Conform also provides a formatexpr, same as the LSP client:

vim.o.formatexpr = "v:lua.require'conform'.formatexpr()"

To view configured and available formatters, as well as to see the log file, run :ConformInfo


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A complete list of all configuration options

  -- Map of filetype to formatters
  formatters_by_ft = {
    lua = { "stylua" },
    -- Conform will run multiple formatters sequentially
    python = { "isort", "black" },
    -- Use a sub-list to run only the first available formatter
    javascript = { { "prettierd", "prettier" } },
    -- Use the "*" filetype to run formatters on all filetypes.
    ["*"] = { "codespell" },
    -- Use the "_" filetype to run formatters on filetypes that don't
    -- have other formatters configured.
    ["_"] = { "trim_whitespace" },
  -- If this is set, Conform will run the formatter on save.
  -- It will pass the table to conform.format().
  -- This can also be a function that returns the table.
  format_on_save = {
    -- I recommend these options. See :help conform.format for details.
    lsp_fallback = true,
    timeout_ms = 500,
  -- If this is set, Conform will run the formatter asynchronously after save.
  -- It will pass the table to conform.format().
  -- This can also be a function that returns the table.
  format_after_save = {
    lsp_fallback = true,
  -- Set the log level. Use `:ConformInfo` to see the location of the log file.
  log_level = vim.log.levels.ERROR,
  -- Conform will notify you when a formatter errors
  notify_on_error = true,
  -- Define custom formatters here
  formatters = {
    my_formatter = {
      -- This can be a string or a function that returns a string
      command = "my_cmd",
      -- OPTIONAL - all fields below this are optional
      -- A list of strings, or a function that returns a list of strings
      -- Return a single string instead to run the command in a shell
      args = { "--stdin-from-filename", "$FILENAME" },
      -- If the formatter supports range formatting, create the range arguments here
      range_args = function(ctx)
        return { "--line-start", ctx.range.start[1], "--line-end", ctx.range["end"][1] }
      -- Send file contents to stdin, read new contents from stdout (default true)
      -- When false, will create a temp file (will appear in "$FILENAME" args). The temp
      -- file is assumed to be modified in-place by the format command.
      stdin = true,
      -- A function that calculates the directory to run the command in
      cwd = require("conform.util").root_file({ ".editorconfig", "package.json" }),
      -- When cwd is not found, don't run the formatter (default false)
      require_cwd = true,
      -- When returns false, the formatter will not be used
      condition = function(ctx)
        return vim.fs.basename(ctx.filename) ~= ""
      -- Exit codes that indicate success (default {0})
      exit_codes = { 0, 1 },
      -- Environment variables. This can also be a function that returns a table.
      env = {
        VAR = "value",
    -- These can also be a function that returns the formatter
    other_formatter = function()
      return {
        command = "my_cmd",

-- You can set formatters_by_ft and formatters directly
require("conform").formatters_by_ft.lua = { "stylua" }
require("conform").formatters.my_formatter = {
  command = "my_cmd",



format(opts, callback)

format(opts, callback): boolean
Format a buffer

Param Type Desc
opts nil|table
timeout_ms nil|integer Time in milliseconds to block for formatting. Defaults to 1000. No effect if async = true.
bufnr nil|integer Format this buffer (default 0)
async nil|boolean If true the method won't block. Defaults to false. If the buffer is modified before the formatter completes, the formatting will be discarded.
formatters nil|string[] List of formatters to run. Defaults to all formatters for the buffer filetype.
lsp_fallback nil|boolean|"always" Attempt LSP formatting if no formatters are available. Defaults to false. If "always", will attempt LSP formatting even if formatters are available.
quiet nil|boolean Don't show any notifications for warnings or failures. Defaults to false.
range nil|table Range to format. Table must contain start and end keys with {row, col} tuples using (1,0) indexing. Defaults to current selection in visual mode
id nil|integer Passed to vim.lsp.buf.format when lsp_fallback = true
name nil|string Passed to vim.lsp.buf.format when lsp_fallback = true
filter nil|fun(client: table): boolean Passed to vim.lsp.buf.format when lsp_fallback = true
callback nil|fun(err: nil|string) Called once formatting has completed


Type Desc
boolean True if any formatters were attempted


list_formatters(bufnr): conform.FormatterInfo[]
Retrieve the available formatters for a buffer

Param Type Desc
bufnr nil|integer


list_all_formatters(): conform.FormatterInfo[]
List information about all filetype-configured formatters

get_formatter_info(formatter, bufnr)

get_formatter_info(formatter, bufnr): conform.FormatterInfo
Get information about a formatter (including availability)

Param Type Desc
formatter string The name of the formatter
bufnr nil|integer


will_fallback_lsp(options): boolean
Check if the buffer will use LSP formatting when lsp_fallback = true

Param Type Desc
options nil|table Options passed to vim.lsp.buf.format


Thanks to

  • nvim-lint for providing inspiration for the config and API. It's an excellent plugin that balances power and simplicity.
  • null-ls for formatter configurations and being my formatter/linter of choice for a long time.