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?

Answer 1

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:

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

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

2. 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
   

3. https://schema.org/docs/jsonldcontext.jsonld gets delivered

   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