FunctionToolCallOutputSerializer

This docs was updated at: 2026-03-21

com.paragon.responses.json.FunctionToolCallOutputSerializer  ·  Class

Extends StdSerializer<FunctionToolCallOutput>

---

Custom Jackson serializer for FunctionToolCallOutput.

The OpenAI Responses API requires:

• type: always "function_call_output"
• call_id: the matching function call ID
• output: a plain string (not an object)

Without this serializer, Jackson would serialize output as a nested JSON object (e.g., {"text": "..."}) because FunctionToolCallOutputKind has no type information. That causes OpenRouter (and OpenAI) to reject the payload with "expected string, received object".

Methods

serializeWithType

public void serializeWithType(
      FunctionToolCallOutput value,
      JsonGenerator gen,
      SerializationContext provider,
      TypeSerializer typeSer)
      throws tools.jackson.core.JacksonException

Called when serializing within a polymorphic context (e.g., List with @JsonTypeInfo). Since we embed "type" directly in the JSON object, we skip the external type wrapper and delegate to .serialize.