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A skill is a filing instruction: it tells whoever is filing an item how to read it, where to put what it contains, and how to record where it came from. Skills are what keep filing consistent, so a meeting filed by your agent ends up looking like a meeting filed by Cortex or by you. Think of skills as the standing instructions pinned above the librarian’s desk. “When a meeting transcript comes in: pull out the attendees, make a page for the meeting dated correctly, note any decisions, and cite the transcript.” Everyone who files follows the same instructions.

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The built-in skills

Cortex’s own filer follows its own version of each filing skill, written for working with nobody present; your agent’s version assumes you are there to ask. Promote and the health check are for agents only. The email skill is narrower than the rest by design: mail may only enter a brain from an address that brain has verified as a forwarder, the agent files it into the brain marked as yours unless you name another, and it confirms before the first thread into a shared or client brain. See your email. There is no skill for splitting or compacting a page any more. The split page and compact page skills that did a model rewrite of a page over the size rule were withdrawn on 7 October 2026, and any copy of them is removed from a workspace the next time it starts. The size rule now applies to what your agent writes; an existing page is never rewritten for its size alone.

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How your agent uses them

When you connect an agent to a brain, these skills are available to it as ready-made instructions. You can lean on them explicitly (“file this using the meeting skill”) or just ask the agent to file something and let it pick the right one. Either way, the result follows the same conventions as everything else in the brain: proper structure, links between related pages, and a citation back to the source. The document skill also sets the order for a file: upload it to the inbox first, read the text Cortex extracts, then write the pages and archive the item. Ask your agent walks through it.

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Consistent by design

The point of skills is that it does not matter who does the filing. Whether Cortex files an item automatically, your agent files it on request, or you file it by hand, the same instructions apply, so a brain stays tidy and predictable however things get into it.