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Comment by podperson | Hacker News Reader

JSON Schema is a schema built on JSON and it’s already being used. Using XML would mean converting the XML into JSON schema to define the response from the LLM.

That said, JSON is “language neutral” but also super convenient for JavaScript developers and typically more convenient for most people than XML.

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Maybe I missed a detail here, sorry if that's the case!

Why would we need to concert XML, which already supports schemas and is well understood by LLMs, back to JSON schema?

Because most of the world uses JSON and has rich tooling for JSONSchemas, notable many LLM providers allow JSONSchemas to be part of the request when trying to get structured output

LLM providers allow sending any string of text though, right? In my experience the LLM understands XML really well, though obviously that doesn't negate them from understanding JSONSchema.

No, it's more than just text now, it's more than just an LLM for the most part now too. They are agentic systems with multiple LLMs, tools, and guardrails

When you provide a JSONSchemea, the result from the LLM is validated in the code between before passing on to the next step. Yes the LLM is reading it too, but non LLM parts of the system use the schema as well

This is arguably much more important for tools and subagents, but also these things are being trained with JSONSchema for tool calling and structured output

LLMs are not people.

We want a format for LLMs or for people?

JSON schema is very human readable.

Why does that matter though? MCP is meant for LLMs not humans, and for something like this lib it seems the human side if the API is based on JavaScript not JSON.

As a person myself, I very much prefer JSON

MCP isn't meant for humans though, I'm not side why it matters what a human would prefer

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