This doesn't seem right:

schema = { "type" => "object", "properties" => { "test" => "string" } }
data = { "test" => "foo" }
JSON::Validator.validate!(schema, data)
=> true

The example is an invalid schema, obviously. It should be:

schema = { "type" => "object", "properties" => { "test" => { "type" => "string" } } }

I tried several other schemata I know to be invalid, such as:

schema = { "type" => "unknown" }

and got the same result.

Shouldn't the correct behavior be to raise an exception when the schema is invalid, or at least return false? This is the behavior of libXML in the XML space, and is also the behavior of several Python implementations of JSON schema.

I plan to investigate this and submit a fix, but wanted to raise the issue first in case this is actually the desired behavior, and if so, ask why.