JSON schema - valid if object does *not* contain a particular property

Question

Is it possible to set up a JSON schema that still allows for additionalProperties but does not match if a very particular property name is present? In other words, I need to know if it's possible to have the exact opposite of the required declaration.

Schema:

{     "type": "object",     "properties": {         "x": { "type": "integer" }     },     "required": [ "x" ],     "ban": [ "z" ] // possible? } 

Match:

{ "x": 123 } 

Match:

{ "x": 123, "y": 456 } 

Do not match:

{ "x": 123, "y": 456, "z": 789 } 

Answer 1

What you want to do can be achieved using the not keyword. If the not schema validates, the parent schema will not validate.

{     "type": "object",     "properties": {         "x": { "type": "integer" }     },     "required": [ "x" ],     "not": { "required": [ "z" ] } } 

Answer 2

There is a simpler approach. Define that if x is present it must not satisfy any schema. By reduction to absurdity x can not be present:

{     "properties" : {         "x" : {             "not" : {}          }     } } 

Update 2020/04/16: As pointed out by @Carsten in a comment, from draft version 05 and above, the proposed schema can be simplified as follows:

{     "properties": {        "x": false     } }