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infoWordPress Core•webwordpresserrorerrorwarningvalidationextensionplugin•star_halfUncommon•warningModerate

Invalid block pattern name

The error occurs when WordPress attempts to register a block pattern whose slug does not follow the required namespace/slug format. The slug must be lowercase, use only alphanumerics and hyphens, and contain a single forward slash.

If the slug is missing, duplicated, or uses a reserved word, the registration fails. WordPress logs a notice and the pattern does not appear in the block inserter.

Symptoms

[dashicons-warning]
PHP notice
Debug log shows a notice about a missing or invalid slug when registering a pattern file.
[dashicons-admin-plugins]
Pattern missing in inserter
Custom pattern does not appear in the Patterns tab of the block inserter.
[dashicons-admin-tools]
Console error
Browser console logs "Invalid block pattern name" while loading block patterns.
[dashicons-admin-site]
Theme activation fallback
WordPress may revert to a default theme if many patterns fail to register.

Common Causes

Malformed slug
Slug does not match the required namespace/slug pattern.
Missing slug metadata
Pattern file lacks a Slug header, so WordPress cannot read the name.
Duplicate slug
Another theme or plugin already registered the same slug.
Reserved word usage
Slug uses a reserved namespace such as core, which is blocked by WordPress.
Early registration
register_block_pattern() runs before the init hook, preventing the registry from accepting the name.
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