RULER + Litellm with Ollama: `ollama_chat` recommended, but `/api/chat` cannot generate required JSON schema

Description

When configuring Ollama via Litellm, the Litellm docs recommend using:

ollama_chat for better responses

This uses Ollama’s /api/chat endpoint.

However, in ART’s RULER integration, the judge model needs to:

• Produce JSON-structured outputs (e.g. match a Pydantic schema / tool schema) so RULER can parse correctness, reasoning, etc.

The problem:

• With Ollama’s /api/chat (via ollama_chat), the responses are not reliably:

  • Valid JSON matching the expected schema, or
  • Tool-call-compatible in the way RULER expects.

• As a result:

  • The judge’s responses often fail schema validation.
  • RULER cannot extract the required fields, and the scoring fails.

Because of that, I’m forced to fall back to the older /api/generate endpoint (ollama), even though:

• Litellm explicitly recommends ollama_chat over ollama.
• /api/chat is the more modern endpoint.

What I expect

• Either:

  • Official support / documentation for using Ollama’s /api/chat (ollama_chat) as a RULER judge with JSON-schema / tool-call style responses; or
  • Clear guidance that for RULER’s JSON-schema needs, we must currently use /api/generate and ollama.

What actually happens

• Using ollama_chat:

  • The /api/chat endpoint does not produce the JSON / tool-call schema RULER expects.
  • Judge calls fail schema validation.

• Using ollama:

  • RULER works better, but we lose out on the newer /api/chat behavior Litellm recommends.

Request

• Please:

  • Document the supported Ollama configuration for RULER (which engine, which endpoint, any special settings).

  • If possible, add direct support for ollama_chat + /api/chat that:

    • Ensures JSON-mode / tool-call style output works with RULER’s structured response expectations.

  • Or provide example configs + templates that make Ollama’s /api/chat usable with RULER.

No files, tests, or entry points are named. Locate RULER's LiteLLM/Ollama judge configuration and reproduce the schema-validation failure with ollama_chat; done means either documented supported configuration and limitations or working /api/chat structured-output support.