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 4

taw1285 12/13/2025|

Curious if anyone has applied this "Skills" mindset to how you build your tool calls for your LLM agents applications?

Say I have a CMS (I use a thin layer of Vercel AI SDK) and I want to let users interact with it via chat: tag a blog, add an entry, etc, should they be organized into discrete skill units like that? And how do we go about adding progressive discovery?

koakuma-chan 12/13/2025||

Does Cursor support skills?

smcleod 12/13/2025|

No I don't believe so. Cursor is usually pretty behind other agentic coding tools in my experience.

retinaros 12/13/2025||

this is really bothering me that we are building abstractions in our language to hide the fact that most of the features are prompts hardcoded in a text file.

structuredPizza 12/13/2025||

tbh everything about the current implementation of "AI" is starting to look like hot porridge when it comes to real world products.

Is the prompting workflow so convenient that it’s worth having to spend twice or thrice as much time double checking the accuracy of the inference and fixing bugs?

How long until we collectively decide that to reduce the probability of errors we’re better off going back to writing our own functions, methods, classes etc. because it gives us granular control?

Last but not least, we’re devolving to mainframe and terminals…

heliumtera 12/13/2025||

So chatgpt can read markdown files? I am very confused

simonw 12/13/2025|

ChatGPT has had a full Linux container system available to it for nearly three years now.

OpenAI keep changing their mind on what to call it. I like the original name, "ChatGPT Code Interpreter", but they've also called it "advanced data analysis" at various points.

Claude added the same feature in September this year: https://simonwillison.net/2025/Sep/9/claude-code-interpreter...

In both ChatGPT and Claude you can say things like "use your Python tool to calculate total mortgage payments over a 30 year period for X and Y" and it will write and execute code to do so - but you can also upload files (including CSVs or even SQLite database files) into that container file system and have them write and execute python code to process those in different ways.

Skills are just folders full of markdown files that are saved in that container when it first boots up.

heliumtera 12/13/2025||

Oooooo, okay. So in fact it has technical capabilities of utilizing and taking advantage of this information provided as skills. That is much clearer now, I appreciate very much your response.

hurturue 12/13/2025||

Github Copilot too

simonw 12/13/2025|

VS Code Copilot just announced experimental skill support in their November release: https://code.visualstudio.com/updates/v1_107#_reuse-your-cla...

ohghiZai 12/13/2025||

Is there a way to implement skills with Gemini?

simonw 12/13/2025||

Looks like they added it to the Gemini CLI public roadmap last week: https://github.com/google-gemini/gemini-cli/issues/11506#eve...

badlogic 12/13/2025||

Create a markdown file, for each SKILL.md of the skills you want to use, put the frontmatter in that single markdown file along with the fulk path to the SKILL.md file. On session start, tell Gemini to read that file. If you put it in your AGENTS.md, you don't have to instruct Gemini. And if you have your skills in a known folder, let Gemini write a small scripts that generates that markdown file for you.

Western0 12/13/2025||

Is possible using skills in ofline models?

simonw 12/13/2025|

Yes, provided they are good enough at long chain tool calling to run a coding agent environment and have a decent context length.

nrhrjrjrjtntbt 12/13/2025|

Quietly? That is a clickbaity adjective.

simonw 12/13/2025|

Yes, but it's also true: OpenAI have said almost nothing in public about their support for skills (there's one tweet about the Codex CLI implementation https://x.com/thsottiaux/status/1995988758886580349 and that's it) while rolling out a pretty major feature - invented by their competitor - to their core 800m+ user product in the past 24 hours.

I think "quietly" is fair.

nrhrjrjrjtntbt 12/13/2025||

Fair point. Other boys cried wolf and made me scepitical.

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