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Comment by kswzzl | Hacker News Reader

> On startup Claude Code / Codex CLI etc scan all available skills folders and extract just those descriptions into the context. Then, if you ask them to do something that's covered by a skill, they read the rest of that markdown file on demand before going ahead with the task.

Maybe I still don't understand the mechanics - this happens "on startup", every time a new conversation starts? Models go through the trouble of doing ls/cat/extraction of descriptions to bring into context? If so it's happening lightning fast and I somehow don't notice.

Why not just include those descriptions within some level of system prompt?

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Yes, it happens on startup of a fresh Claude Code / Codex CLI session. They effectively get pasted into the system prompt.

Reading a few dozen files takes on the order of a few ms. They add enough tokens per skill to fit the metadata description, so probably less than 100 for each skill.

So when it says:

> The body can contain any Markdown; it is not injected into context.

It just means it's not injected into the context until the skill is used or it's never injected into the context?

https://github.com/openai/codex/blob/main/docs/skills.md

Yeah, that means that the body of that file will not be injected into the context on startup.

I had thought that once the skill is selected the whole file would be read, but it looks like that's not the case: https://github.com/openai/codex/blob/ad7b9d63c326d5c92049abd...

  1) After deciding to use a skill, open its `SKILL.md`. Read only enough to follow the workflow.

So you could have a skill file that's thousands of lines long but if the first part of the file provides an outline Codex may stop reading at that point. Maybe you could have a skill that says "see migrations section further down if you need to alter the database table schema" or similar.

Knowing Codex, I wonder if it might just search for text in the skill file and read around matches, instead of always reading a bit from the top first.

Can models actually stream the file in as they see fit, or is "read only enough" just an attention trick? I suspect the latter.

Depends the agent, they can read in chunks (i.e.: 500 lines at a time)

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