# Cache-Busting Versions Based on File Changes

> Replaces the version number on your theme's and plugins' CSS and JavaScript URLs with the file's last-modified time, so browsers and CDNs cache files for a long time but always fetch a fresh copy right after you change one.

- Type: PHP
- Runs: Frontend only
- Category: [Performance](https://wpide.com/library/category/performance/)
- Tags: cache-busting, css, javascript
- Author: WPIDE Team
- Installs: 0
- Updated: 2026-10-28
- Page: https://wpide.com/library/perf-filemtime-asset-versions/

## Code

```php
$wpide_mtime_version = function ( $src ) {
    if ( ! is_string( $src ) || false !== strpos( $src, '/wp-includes/' ) || false !== strpos( $src, '/wp-admin/' ) ) {
        return $src;
    }

    $content_url = set_url_scheme( content_url(), 'https' );
    $clean       = set_url_scheme( strtok( $src, '?' ), 'https' );

    if ( 0 !== strpos( $clean, $content_url ) ) {
        return $src;
    }

    $path = WP_CONTENT_DIR . substr( $clean, strlen( $content_url ) );

    if ( false !== strpos( $path, '..' ) || ! is_file( $path ) ) {
        return $src;
    }

    return add_query_arg( 'ver', (string) filemtime( $path ), $src );
};

add_filter( 'style_loader_src', $wpide_mtime_version, 15 );
add_filter( 'script_loader_src', $wpide_mtime_version, 15 );
```

## Notes

File times are cached in memory for the request; WordPress core files keep their normal version.

## How to use it

Install the free WPIDE plugin (https://wordpress.org/plugins/wpide/), find "Cache-Busting Versions Based on File Changes" in its snippet library and add it in one click; or create a new PHP snippet in WPIDE (or any code snippets plugin) and paste the code above. More snippets: https://wpide.com/library/