How to Fix – Rank Math Fatal: “Missing format specifier at end of string”

If Rank Math throws Fatal error: Uncaught ValueError: Missing format specifier at end of string (often in includes/frontend/class-breadcrumbs.php), the issue is almost always a malformed sprintf() format in your Breadcrumbs text (for example a stray % or a missing %s). Here’s the quick recovery and the permanent fix.

My site crashes with “ValueError: Missing format specifier at end of string” from Rank Math (class-breadcrumbs.php). How do I fix this without disabling the plugin?

This error means a text string Rank Math passes to sprintf() isn’t valid (for example, it ends with a lone % or the number of placeholders doesn’t match). The most common source is a customized Breadcrumbs label. Fix it like this:

Quick recovery

Temporarily disable Rank Math (if you’re locked out):
```
wp plugin deactivate seo-by-rank-math
```
Then log in, and reactivate after you adjust the settings below.

Permanent fix (Breadcrumbs formats)

Go to WordPress Dashboard → Rank Math SEO → General Settings → Breadcrumbs.
Review every text field that can contain a placeholder (examples vary by version/theme integration):
- Search Results Format should include %s (e.g., Results for %s).
- Author Archives Format, Date Archives, 404 label, etc. If they use placeholders, make sure they’re valid (e.g., Articles by %s).
Remove any stray “%” at the end of a string and ensure the number of %s matches the values Rank Math injects.
Click Save, then clear caches (page cache, Rank Math/SEO plugin cache if applicable, and any CDN).
Update Rank Math to the latest version.

Common examples (good vs. bad)

Good: Results for %s
Bad: Results for % (missing the s)
Bad: Results for %s% (extra % at the end)

If you use translations or custom code

Translations (WPML/Polylang/Loco): Make sure translated strings preserve the %s placeholder exactly. A missing or extra % will fatal on PHP 8+.

Theme overrides / filters: If you customize breadcrumb labels in code, ensure your format string and arguments line up:

add_filter( 'rank_math/breadcrumbs/search_format', function( $format ) {
    // Always include %s for the search query:
    return 'Results for %s';
});

Verify the fix

Enable debug logging (temporarily) if needed:

define( 'WP_DEBUG', true );
define( 'WP_DEBUG_LOG', true );
define( 'WP_DEBUG_DISPLAY', false );

Reload the page that previously crashed. The fatal should be gone, and breadcrumbs should render normally.

Why this happens on PHP 8+

PHP 8 turned many formatting mistakes into hard ValueError exceptions. If a breadcrumb label contains a malformed % sequence, sprintf() now throws a fatal instead of a notice/warning, hence the crash.

Still seeing the error after fixing Breadcrumbs? Check any plugin/theme strings that filter Rank Math breadcrumbs and ensure their placeholders (%s, etc.) are valid and in the right count.