How do I embed Vim settings inside a file using modelines?

Explanation

Modelines are special comments at the top or bottom of a file that Vim reads to apply file-specific settings. They let you enforce coding standards per-file — indentation, textwidth, filetype — without relying on project-wide configuration.

How it works

• Place the modeline in the first or last 5 lines of the file
• Format: vim: set {options}: or vim: {options}
• Vim reads modelines automatically if modeline option is enabled
• Settings are applied as :setlocal (file-local only)

Example

# Python file with 4-space indentation
# vim: set ts=4 sw=4 et:

// JavaScript file with 2-space indentation
// vim: set ts=2 sw=2 et:

/* C file with tabs */
/* vim: set noet ts=8 sw=8: */

Tips

• modelines option controls how many lines are checked (default 5)
• Modelines run in sandbox mode for security — they can't execute shell commands
• Common options: ts (tabstop), sw (shiftwidth), et (expandtab), tw (textwidth), ft (filetype)
• Disable modelines for security: :set nomodeline (risky files from untrusted sources)