How can http://schema.org be used in JSON-LD's @context, even though it's not a JSON-LD file?

Question

As far as I can see in the JSON-LD spec, section 3.1 - The Context, @context can either be:

an inline JSON object:

{ "@context": { "name": "http://schema.org/name" } }

or a string representing the URI of an external JSON-LD file containing such a JSON object:
```
{ "@context": "https://json-ld.org/contexts/person.jsonld" } 
```

However, when used with the schema.org vocabulary, @context is always used this way:

{ "@context": "http://schema.org", }

Even though http://schema.org is not the URI of a JSON-LD document.

What did I miss?

unor · Accepted Answer · 2019-06-11 20:48:32Z

Schema.org uses content negotiation to provide the JSON-LD context file.

If you request http://schema.org while sending the request header that you accept/prefer application/ld+json, this is what happens:

http://schema.org 301-redirects to https://schema.org/

HTTP/1.1 301 Moved Permanently Content-Type: text/html Location: https://schema.org/

https://schema.org/ 302-redirects to https://schema.org/docs/jsonldcontext.jsonld

HTTP/1.1 302 Found Content-Type: text/html; charset=utf-8 Location: https://schema.org/docs/jsonldcontext.jsonld

HTTP/1.1 200 OK Content-Type: application/ld+json; charset=utf-8

You can test it yourself with curl:

curl -L -H "Accept: application/ld+json" http://schema.org

-L makes curl follow redirects
-H includes the following header (Accept: application/ld+json) in the request

It did not even cross my mind that content negotiation could be used in this context. This makes perfect sense. Thank you! — BenMorel
– BenMorel, Commented Jun 11, 2019 at 23:22
My understanding is that as of writin jsonld instead relies on the HTTP Link header to retrieve jsonld contexts. You can verify it by running curl -IL http://schema.org. Check out w3.org/TR/json-ld11-api/#loaddocumentcallback for the current algorithm. — Maciej Goszczycki
– Maciej Goszczycki, Commented Jun 17, 2020 at 13:44

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