How to query on contact via Rest API


Referring -

Is there any option available in Rest API to get all contacts with a specific condition (Query).
For Example list of all contacts who have a blank value of a custom field

Thanks in advance!

Not specifically that I can see but there are a couple of ways to still handle that.

  1. REST webhooks (contact.edit) would allow you to check any updated contacts for an empty custom field.
  2. the XML-RPC api would allow you to query a list of all contacts with an empty custom field.