RULER produces scores >1, arbitrary outputs (7, 10, 15…), nondeterministic behavior, and malformed JSON when judge model is Qwen3-32B running on Ollama

[ansh-info]

What happened?

I’m running ART’s RULER scoring step using a local Ollama server (on a machine with 2× H100 80GB) hosting:

• Qwen3-32B (tried both quantized + full FP16, which uses ~66GB VRAM)
• Serving as the LLM judge inside ruler() / ruler_score_group()

However, RULER often produces invalid or nonsensical outputs, specifically:

1. RULER returns scores >1 (e.g., 7, 10, 15)

Even though the schema requires:

score: float  # between 0 and 1

I frequently get outputs like:

• score: 7
• score: 10
• score: 15
• or other arbitrary integers / floats

Sometimes the score is actually "10" (string), "1.", "0.8x", etc.

This violates the API contract and breaks training.

---

2. RULER gives hallucinated/meaningless scores per trajectory

Even when trajectories look similar or follow the system instructions, the judge:

• Randomly assigns very high or very low scores
• Ignores the rubric
• Produces wildly different outputs across runs (no determinism)
• Sometimes gives no comparison at all, just arbitrary values

---

3. JSON returned by judge is malformed or incomplete

Very often, the content inside:

first_choice.message.content

is:

• Partial JSON
• Badly formatted JSON
• JSON containing stray characters
• Missing required fields (trajectory_id, explanation, etc.)
• A mixture of plaintext + JSON fragments
• Sometimes entirely non-JSON despite RULER passing a Pydantic response_format

This triggers failures like:

pydantic_core._pydantic_core.ValidationError: JSON parsing error

or:

json.decoder.JSONDecodeError

I even had to introduce a fallback parser because well-formed JSON simply does not arrive reliably.

---

4. RULER’s behavior is nondeterministic even with same prompt + same trajectories

Across repeated runs:

• Same trajectories produce different scores
• Sometimes >1, sometimes valid (0.3), sometimes JSON errors
• Even with FP16 full-precision version of Qwen3-32B (66GB VRAM) and temperature = 0

This strongly suggests the judge model is not following the system prompt reliably.

---

Why I believe this is an ART / RULER robustness issue

Looking at the code inside ruler():

response = await acompletion(
    model=judge_model,
    messages=messages,
    response_format=Response,
    caching=False,
)
...
content = first_choice.message.content or "{}"
parsed = Response.model_validate_json(content)

RULER assumes:

1. The backend model supports strict JSON mode
2. The returned content is fully compliant with the Pydantic schema
3. The judge will obey the system prompt, including scoring between 0 and 1

But these assumptions do not always hold for:

• Ollama models
• Qwen3-32B, which does not have deterministic structured output
• Non-OpenAI providers through LiteLLM

Ollama cannot guarantee strict JSON output, and model behavior varies even at temperature 0.

As a result:

• RULER collapses when JSON isn’t perfect
• Scoring becomes arbitrary / hallucinated
• Training reward curves become meaningless

This matches exactly the issues I’m seeing.

---

What I expected to happen

• If response_format=Response is provided, the judge should reliably produce JSON
• Scores should always be in [0, 1]
• Behavior should be deterministic (or configurable)
• RULER should gracefully handle imperfect JSON (or allow a custom parse)
• Models that cannot reliably produce JSON should not break the entire training run

---

Actual behavior

• Scored values frequently outside the allowed range
• JSON formatting frequently invalid
• Judge fails to follow rubric
• Behavior nondeterministic across runs
• Leads to failed training steps, invalid reward gradients, and incorrect trajectory ranking

---

Why this matters

RULER is advertised as:

“A general-purpose reward function for RL agents”

But in practice, with non-OpenAI models (e.g., local HPC deployment via Ollama), RULER’s strict JSON assumptions break repeatedly.

A growing number of users want:

• local inference
• open models
• offline training
• privacy and cost control

But RULER currently assumes an OpenAI-style JSON-mode model.

---

Suggested solutions

Here are concrete changes that would fix or improve the situation:

1. Add clamping for scores

Automatically:

score = max(0.0, min(1.0, score))

This immediately resolves the “score > 1” crashes.

2. Add a robust JSON extraction / correction layer

e.g.:

• extract the first valid JSON block
• filter out stray characters
• fallback to regex extraction

3. Allow a user-defined parse_response() hook

For example:

async def ruler(..., parse_response: Callable[[ModelResponse], Response] = None)

4. Add a validation step in RULER that warns when the judge cannot follow JSON-mode

Instead of crashing training.

5. Recommend judges known to produce reliable JSON

Or explicitly warn that models like Qwen3-32B (via Ollama) may not be JSON-mode safe.

---

Environment

• 2× NVIDIA H100 80GB
• Ollama server hosting Qwen3-32B (both quantized + full FP16 variants)
• LiteLLM router
• ART latest version (2025)
• RULER used via ruler_score_group()
• Temperature = 0

---

I can also provide logs + trajectories if needed.

But the core issue is that RULER's strict JSON-mode expectations do not hold for many models, leading to:

• hallucinated scores
• invalid reward signals
• malformed JSON
• nondeterministic judge behavior