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Comment by mac-mc | Hacker News Reader

You're missing the most significant lesson of all that MCP knew. That all of those featureful things are way too overcomplicated for most places, so they will gravitate to the simple thing. It's why JSON over HTTP blobs is king today.

I've been on the other side of high-feature serialization protocols, and even at large tech companies, something like migrating to gRPC is a multi-year slog that can even fail a couple of times because it asks so much of you.

MCP, at its core, is a standardization of a JSON API contract, so you don't have to do as much post-training to generate various tool calling style tokens for your LLM.

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Gall’s Law: all complex systems that work evolved from simpler systems that worked.

What are HTTP blobs?

I think you meant that is why JSON won instead of XML?

JSON-over-HTTP blobs. Or blobs of schemaless json.

Not just XML, but a lot of other serialization formats and standards, like SOAP, protobuf in many cases, yaml, REST, etc.

People say REST won, but tell me how many places actually implement REST or just use it as a stand-in term for casual JSON blobs to HTTP URLs?

So, I just looked it up, thinking I might have overlooked something but, at least according to wikipedia, REST does not prescribe the format of the data transferred. So, I don't understand why you are comparing REST to xml, yaml, json or whatever.

Now, YAML has quite a few shortcomings compared to JSON (if you don't believe me, look at its handling of the string no, discussed on HN), so, at least to me, it's obvious why JSON won.

SOAP, don't get me started on that, it's worth less than XML, protobuf is more efficient but less portable, etc.

JSON won because it’s what JavaScript in browsers understands natively. That’s also the reason why JSON even exists in the first place.

And who decided that? Why not XML?

That's backwards reasoning. XML was too complicated, so they decided on a simpler JSON.

XML has been supported in javascript for essentially just as long as JSON, arguably longer. Heck, the first in-practice and standardized HTTP request APIs for javascript were "XMLHTTPRequest" (and similar "XMLHTTP" names). And XHTML is a thing, and it predates both JSON and AJAX.

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