OpenAI are quietly adopting skills, now available in ChatGPT and Codex CLI

Posted by simonw 12/12/2025

OpenAI are quietly adopting skills, now available in ChatGPT and Codex CLI(simonwillison.net)

587 points | 324 commentspage 2

mehdibl 12/13/2025|

This is killing me with complexity. We had agents.md and were supposed to augment the context there. Now back to cursor rules and another md file to ingest.

simonw 12/13/2025||

MCPs feel complicated. Skills seem to me like the simplest possible design for a mechanism for adding extra capabilities to an existing coding agent.

febed 12/14/2025||

Can skills completely replace MCPs? For example, can a skill be configured to launch my local Python program in its own venv. I don’t want Claude to spend time spinning up a runtime

simonw 12/14/2025||

Skills only work if you have a code environment up and running and available for a coding agent to execute commands in.

You can absolutely have a skill that tells the coding agent how to use Python with your preferred virtual environment mechanism.

I ended up solving that in a slightly different way - I have a Claude hook that spits attempts to run "python" or "python3" and returns an error saying "use uv run instead".

delaminator 12/13/2025|||

I tell Claude to make its own skills. “Which part of this task is worth making a skill for, use your skill making skill to do it”

baq 12/13/2025||

If we aren’t in the take off phase, I don’t know where we are

rafaquintanilha 12/13/2025||

Skills are just pointers to context so you don't need to load all of them upfront, it is as simple as that. By the way cursor rules is effectively the same as agents.md.

dsiegel2275 12/13/2025||

This is great that Codex CLI is adding skills - but it would be far more useful if the CLI looked first in the project (the directory where I've launched codex) `.codex/skills` directory and THEN the home directory .codex dir. The same issue exists for prompts.

Fannon 12/13/2025||

This is nice, but that it goes into its vendor specific .codex/ folder is a bit of a drag.

I hope such things will be standardized across vendors. Now that they founded the Agentic AI Foundation (AAIF) and also contributed AGENTS.md, I would hope that skills become a logical extension of that.

https://www.linuxfoundation.org/press/linux-foundation-annou...

https://aaif.io/

diwank 12/19/2025||

GitHub Copilot now supports Agent Skills

https://github.blog/changelog/2025-12-18-github-copilot-now-...

robkop 12/13/2025||

Hasn’t ChatGPT been supporting skills with a different name for several months now through “agent”?

They gave it back then folders with instructions and executable files iirc

simonw 12/13/2025|

Not quite the same thing. Implementing skills specifically means that you have code which, on session start, scans the skills/*/skill.md files and reads in their description: metadata and loads that into the system prompt, along with an instruction that says "if the user asks about any of these particular things go and read the skills.md file for further instructions".

Here's the prompt within Codex CLI that does that: https://github.com/openai/codex/blob/ad7b9d63c326d5c92049abd...

I extracted that into a Gist to make it easier to read: https://gist.github.com/simonw/25f2c3a9e350274bc2b76a79bc8ae...

robkop 12/13/2025||

I remember you did some reverse engineering when they released agent, does it not feel quite similar to you?

I know they didn’t dynamically scan for new skill folders but they did have mentions of the existing folders (slides, docs, …) in the system prompt

simonw 12/13/2025||

The main similarity is that both of them take full advantage of the bash tool + file system combination.

jstummbillig 12/13/2025||

Is there a fundamental difference between a skill and a tool or could I just make a terse skill and have that be used in the same way as a tool?

Imanari 12/13/2025|

I think a tool call can be thought of as special type of reply where it’s contents are parsed and an actual function is called. A skill is more of a dynamic context-enrichment.

lynx97 12/13/2025||

@simonw: Any particular reason you stopped releasing "llm" regularily? I believe the last release was done in summer. Neither gpt-5.1 nor gpt-5.2 have been added. Are you about to give up on that project? Is it time to search for another one?

I also have an open issue since months, which someone wrote a PR for (thanks") a few weeks ago.

Are you still comitted to that project?

simonw 12/13/2025|

I shipped a new release yesterday - https://llm.datasette.io/en/stable/changelog.html#v0-28 but yeah, the last core release before that was in August. I've been pushing out plugin releases for it though, for new models from Gemini and Anthropic and others.

Honestly the main problem has been that LLM's unique selling point back in 2024 was that it was the only tool taking CLI access to LLMs seriously. In 2025 Claude Code and Codex CLI etc all came along and suddenly there's not much unique about having a CLI tool for LLMs any more!

There's also a major redesign needed to the database storage and model abstraction layer in order to handle reasoning traces and more complex tool call patterns. I opened an issue about that here - it's something I'm stewing on but will take quite some work to get right: https://github.com/simonw/llm/issues/1314

I've been spending more of my time focusing on other projects which make use of LLM, in particular Datasette plugins that use the asyncio Python library: https://llm.datasette.io/en/stable/python-api.html#async-mod...

I expect those to drive some core improvements pretty soon.

rokoss21 12/13/2025||

This is a clever abstraction. Reminds me of how tool_use worked in earlier Claude versions - defining a schema upfront and letting the model decide when to call it.

Has anyone tested how well this works with code generation in Codex CLI specifically? The latency on skill registration could matter in a typical dev workflow.

bzmrgonz 12/13/2025||

It is interesting that they are relying on visual reading for document ingestion instead of OCT. Recently I read an article which says Handwriting recognition has matured, and I'm beginning to think this is the approach they are takingwirh HAndwiting recognition.

jaco6 12/13/2025|

[dead]

wskish 12/16/2025|

Skills are basically (on-demand) man pages for other libraries or cli tools, or SOPs for other more complex processes. A beautiful, minimal abstraction.

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