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A filter is a special-purpose built-in function. It is used to evaluate on each message in a pipeline and is often used to filter the number of messages that are passed to next vertices.

Filter function supports comprehensive expression language which extend flexibility write complex expressions.

payload will be root element to represent the message object in expression.


Filter expression implemented with expr and sprig libraries.

Data conversion functions

These function can be accessed directly in expression.

  • json - Convert payload in JSON object. e.g: json(payload)
  • int - Convert element/payload into int value. e.g: int(json(payload).id)
  • string - Convert element/payload into string value. e.g: string(json(payload).amount)

Sprig functions

Sprig library has 70+ functions. sprig prefix need to be added to access the sprig functions.

sprig functions


  • sprig.contains('James', json(payload).name) # James is contained in the value of name.
  • int(json(sprig.b64dec(payload)).id) < 100

Filter Spec

- name: filter-vertex
      name: filter
        expression: int(json(payload).id) < 100