Simon Willison’s Weblog

model.yaml. From their GitHub repo it looks like this effort quietly launched a couple of months ago, driven by the LM Studio team. Their goal is to specify an "open standard for defining crossplatform, composable AI models".

A model can be defined using a YAML file that looks like this:

model: mistralai/mistral-small-3.2
base:
  - key: lmstudio-community/mistral-small-3.2-24b-instruct-2506-gguf
    sources:
      - type: huggingface
        user: lmstudio-community
        repo: Mistral-Small-3.2-24B-Instruct-2506-GGUF
metadataOverrides:
  domain: llm
  architectures:
    - mistral
  compatibilityTypes:
    - gguf
  paramsStrings:
    - 24B
  minMemoryUsageBytes: 14300000000
  contextLengths:
    - 4096
  vision: true

This should be enough information for an LLM serving engine - such as LM Studio - to understand where to get the model weights (here that's lmstudio-community/Mistral-Small-3.2-24B-Instruct-2506-GGUF on Hugging Face, but it leaves space for alternative providers) plus various other configuration options and important metadata about the capabilities of the model.

I like this concept a lot. I've actually been considering something similar for my LLM tool - my idea was to use Markdown with a YAML frontmatter block - but now that there's an early-stage standard for it I may well build on top of this work instead.

I couldn't find any evidence that anyone outside of LM Studio is using this yet, so it's effectively a one-vendor standard for the moment. All of the models in their Model Catalog are defined using model.yaml.

# 21st June 2025, 5:15 pm / standards, yaml, ai, generative-ai, llms, llm, lm-studio

openai/openai-openapi. Seeing as the LLM world has semi-standardized on imitating OpenAI's API format for a whole host of different tools, it's useful to note that OpenAI themselves maintain a dedicated repository for a OpenAPI YAML representation of their current API.

(I get OpenAI and OpenAPI typo-confused all the time, so openai-openapi is a delightfully fiddly repository name.)

The openapi.yaml file itself is over 26,000 lines long, defining 76 API endpoints ("paths" in OpenAPI terminology) and 284 "schemas" for JSON that can be sent to and from those endpoints. A much more interesting view onto it is the commit history for that file, showing details of when each different API feature was released.

Browsing 26,000 lines of YAML isn't pleasant, so I got Claude to build me a rudimentary YAML expand/hide exploration tool. Here's that tool running against the OpenAI schema, loaded directly from GitHub via a CORS-enabled fetch() call: https://tools.simonwillison.net/yaml-explorer#.eyJ1c... - the code after that fragment is a base64-encoded JSON for the current state of the tool (mostly Claude's idea).

The tool is a little buggy - the expand-all option doesn't work quite how I want - but it's useful enough for the moment.

Update: It turns out the petstore.swagger.io demo has an (as far as I can tell) undocumented ?url= parameter which can load external YAML files, so here's openai-openapi/openapi.yaml in an OpenAPI explorer interface.

# 22nd December 2024, 10:59 pm / apis, tools, yaml, ai, openai, generative-ai, llms, ai-assisted-programming, claude-3-5-sonnet

airtable-export. I wrote a command-line utility for exporting data from Airtable and dumping it to disk as YAML, JSON or newline delimited JSON files. This means you can backup an Airtable database from a GitHub Action and get a commit history of changes made to your data.

# 29th August 2020, 9:48 pm / json, projects, yaml, airtable

twitter-text-conformance (via) This is a neat idea: Twitter have released open source libraries for parsing standard tweet syntax in Ruby and Java, but they’ve also released a set of YAML unit tests aimed at anyone who wants to implement the same parsing logic in other languages.

# 6th February 2010, 3:39 pm / java, ruby, testing, twitter, yaml, conformance-suites