x-nananana: Batcache

The header Batcache, Automattic's WordPress page cache, uses to say a page came from the cache, named with the Batman theme.

Batcache is a memcached-backed full-page cache for WordPress, written at Automattic and used on WordPress.com and the hosts built on its stack. Its source opens with the comment nananananananananananananananana BATCACHE!!!, and the production deployments answer with a header named x-nananana whose value reports the cache state, Batcache-Hit when the page was served from the cache. Pressable's documentation tells customers to look for exactly that header to confirm the cache is working. It is a diagnostic header that happens to be a joke, which is the rarest and best kind: it earns its place in the response and smiles while it does.

Also known as: X-nananana, Batcache header, nananana Batcache

Sources

Pressable knowledge base, 'How does Batcache page caching work': if Batcache is active you should see x-nananana Batcache-Hit under the response headers
Automattic/batcache, advanced-cache.php: the source comment 'nananananananananananananananana BATCACHE!!!' at the top of the page cache

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