Example of a simple custom JSON-LD context

custom.jsonld

{
   "@context":{
      "label":"http://www.w3.org/2000/01/rdf-schema#label",
      "xsd":"http://www.w3.org/2001/XMLSchema#",
      "ext":"http://example.org/jsonld#",
      "id":"@id"
   },
   "ext:myCustomProperty":{
      "id":"ext:myCustomProperty",
      "label":"This is the label"
   },
   "ext:myNumericProperty":{
      "id":"ext:myNumericProperty",
      "label":"This is a property with a number value",
      "@type":"xsd:integer"
   },
   "ext:myURLProperty":{
      "id":"ext:myURLProperty",
      "label":"This is a property with a URI value",
      "@type":"@id"
   }
}

example.jsonld

{
  "@context": [
    "https://www.openactive.io/ns/oa.jsonld",
    "https://gist.githubusercontent.com/ldodds/932e46e2459775d0ef8c3978866a745a/raw/e561eb4fba120764d6f36c0f8544cb33dd226301/custom.jsonld"
  ],
  "type": "Event",
  "ext:myCustomProperty": "foo"
}