Format JSON in Vim with jq

Contents

• Introduction
• The jq command
• Set keymaps
• Create AutoCommand
• Set as Vim’s default formatter
• Conclusion

Introduction

You can run external commands like sort, echo, git, etc. in Vim command-mode.

With jq installed, you can run jq command and format JSON files inside Vim.

The jq command

:%!jq Format (pretty-print) code in file.

:.!jq Format code in current line.

:%!jq -c Compact output with -c or --compact-output flag.

Check jq man page for more.

% represents current file, while . represents current line.

Set keymaps

If you frequently run these commands, you can bind them to a key.

For example, map CTRL+J to run the :%!jq command in Vim:
noremap <C-j> :%!jq<CR>

The same binding for Neovim in Lua:
vim.keymap.set('n', '<C-j>', ':%!jq<CR>', {desc="Pretty-print JSON"})

Create AutoCommand

Another cool trick would be to create an AutoCommand to automatically run these commands on file write.

Here’s how to set one in Neovim:

-- Auto format JSON on write
vim.api.nvim_create_autocmd('BufWritePre', {
  group = vim.api.nvim_create_augroup('format-file', {}),
  pattern = '*.json',
  command = ':%!jq'
})

Set as Vim’s default formatter

Pressing gq + motion formats file using Vim’s built in format program.

We can set jq as the default format program for JSON files with:
set formatprg="jq".

Conclusion

You can lookup and use different formatters for different file types. The possibilities are limitless in Vim.