, does Activiti provide something like RAML, to help quickly generate a client?

[jacobzhou]

just could not find  in the API document

[cjose]

Yes, the swagger (open api spec) definition is available from Activiti version 6 onwards - Activiti/activiti.json at 6.x · Activiti/Activiti · GitHub. There is currently no RAML files available for the community version. 

If you are using Alfresco Process Services (enterprise version) the swagger & raml files of the enterprise apis are also available in the product.