OpenAPIToolset: INVALID_ARGUMENT due to oneOf keyword

[joaquinperaza]

Describe the bug

The agent is raising an INVALID_ARGUMENT error claiming that parameters.properties cannot be empty.
However, the actual issue appears to stem from a misunderstanding of the OpenAPI schema for the endpoint /api/logs/.

The schema defines Log as a polymorphic object with a discriminator, and supports multiple subtypes using oneOf. This should be valid according to the OpenAPI specification, but the agent fails to handle it correctly.

Full error message

{
  "error": "400 INVALID_ARGUMENT. {'error': {'code': 400, 'message': '* GenerateContentRequest.tools[0].function_declarations[52].parameters.properties[]: key cannot be empty\n*"
}

Relevant Schema

Log:
  oneOf:
    - $ref: '#/components/schemas/SowingTyped'
    - $ref: '#/components/schemas/PhenologyTyped'
    - $ref: '#/components/schemas/WaterTyped'
    - $ref: '#/components/schemas/YieldTyped'
    - $ref: '#/components/schemas/FertilizationTyped'
    - $ref: '#/components/schemas/ApplicationTyped'
    - $ref: '#/components/schemas/LabReportTyped'
    - $ref: '#/components/schemas/FieldReportTyped'
    - $ref: '#/components/schemas/BugReportTyped'
    - $ref: '#/components/schemas/WeedReportTyped'
    - $ref: '#/components/schemas/DisesaseReportTyped'
  discriminator:
    propertyName: type
    mapping:
      Sowing: '#/components/schemas/SowingTyped'
      Phenology: '#/components/schemas/PhenologyTyped'
      Water: '#/components/schemas/WaterTyped'
      Yield: '#/components/schemas/YieldTyped'
      Fertilization: '#/components/schemas/FertilizationTyped'
      Application: '#/components/schemas/ApplicationTyped'
      LabReport: '#/components/schemas/LabReportTyped'
      FieldReport: '#/components/schemas/FieldReportTyped'
      BugReport: '#/components/schemas/BugReportTyped'
      WeedReport: '#/components/schemas/WeedReportTyped'
      DiseaseReport: '#/components/schemas/DisesaseReportTyped'

/api/logs/:
  get:
    operationId: api_logs_list
    parameters:
      - in: query
        name: polymorphic_ctype
        schema:
          type: integer
    tags:
      - api
    security:
      - tokenAuth: []
    responses:
      '200':
        description: ''
        content:
          application/json:
            schema:
              type: array
              items:
                $ref: '#/components/schemas/Log'

Steps to reproduce

1. Include the schema above in the OpenAPI spec.
2. Load the spec using OpenAPIToolset
3. Attempt to load the endpoint using adk web
4. See the INVALID_ARGUMENT error from tool generation.

Expected behavior

The agent should recognize the discriminator and oneOf structure as a valid schema definition and generate appropriate tools without raising a malformed parameters.properties[] error.

Desktop

OS: macOS Sequoia
Python version: python 3.13
ADK version: 1.2.1

Model Information: gemini-2.5-pro

[GWeale]

Tested on latest ADK and confirmed that using oneOf with a discriminator works as expected with OpenAPIToolset. Tools generate without the INVALID_ARGUMENT error.

components:
  schemas:
    Log:
      oneOf:
        - $ref: '#/components/schemas/SowingTyped'
        - $ref: '#/components/schemas/PhenologyTyped'
      discriminator:
        propertyName: type
        mapping:
          Sowing: '#/components/schemas/SowingTyped'
          Phenology: '#/components/schemas/PhenologyTyped'
    SowingTyped:
      type: object
      properties:
        type:
          type: string
        seeds:
          type: integer
    PhenologyTyped:
      type: object
      properties:
        type:
          type: string
        stage:
          type: string

I’m closing this out since oneOf works on the latest code. If you still encounter issues, please share a minimal spec and version details and we can reopen.

[joaquinperaza]

Thanks for following up on this issue! Unfortunately I tried using the latest version without any progress:

[[package]]
name = "google-adk"
version = "1.11.0"

However, after digging deeper into my OpenAPI spec, I found a significant difference compared to your example:

    SowingTyped:
      allOf:
      - type: object
        properties:
          type:
            type: string
        required:
        - type
      - $ref: '#/components/schemas/Sowing'

I will try to replicate this issue with a minimal spec.

[joaquinperaza]

@GWeale I am not able to run adk web using this minimal example that includes the schema you marked as valid:

from google.adk.tools.openapi_tool.openapi_spec_parser.openapi_toolset import OpenAPIToolset
from google.adk.agents import Agent

minimal_problematic_spec = """
openapi: 3.0.0
info:
  title: Minimal API to Reproduce Malformed Tool Issue
  version: 1.0.0
servers:
  - url: https://api.example.com
paths:
  /api/logs/:
    post:
      operationId: api_logs_create
      tags:
        - api
      requestBody:
        content:
          application/json:
            schema:
              $ref: '#/components/schemas/Log'
      security:
        - tokenAuth: []
      responses:
        '201':
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/Log'
          description: ''
components:
  securitySchemes:
    tokenAuth:
      type: http
      scheme: bearer
  schemas:
    Log:
      oneOf:
        - $ref: '#/components/schemas/SowingTyped'
        - $ref: '#/components/schemas/PhenologyTyped'
      discriminator:
        propertyName: type
        mapping:
          Sowing: '#/components/schemas/SowingTyped'
          Phenology: '#/components/schemas/PhenologyTyped'
    SowingTyped:
      type: object
      properties:
        type:
          type: string
        seeds:
          type: integer
    PhenologyTyped:
      type: object
      properties:
        type:
          type: string
        stage:
          type: string
"""

api_toolset = OpenAPIToolset(
    spec_str=minimal_problematic_spec,
    spec_str_type="yaml",
)

root_agent = Agent(
    name="APICALLER",
    model="gemini-2.5-pro",
    description="YOU DO API CALLS",
    instruction="YOU CALL THE API MANY TIMES",
    tools=[api_toolset],
)

I am using adk version 1.11.0, and the error appears after the first user interaction that calls the API (might be a silent failure if not called). If this example is also not working on your end I'd recommend reopening the issue until it gets fixed. Also it would be great if the nested oneOf/allOf can be tested using this minimal spec with the agent example:

schemas:
    Log:
      oneOf:
        - $ref: '#/components/schemas/SowingTyped'
      discriminator:
        propertyName: type

    SowingTyped:
      allOf:
        - type: object
          properties:
            type:
              type: string
          required:
            - type
        - $ref: '#/components/schemas/Sowing'

    Sowing:
      type: object
      properties:
        seeds_kg_ha:
          type: number