Reward Rubrics - Osmosis API

Reward rubrics leverage LLMs to evaluate outputs using natural language criteria. They use the @osmosis_rubric decorator and delegate scoring to a language model based on a rubric description.

Basic Example

File: reward_rubric/reward_rubric_openai.py

from osmosis_ai import evaluate_rubric, osmosis_rubric
import os

RUBRIC = "Reward based on whether the predicted numerical value matches the ground truth."
SCORE_MIN = 0.0
SCORE_MAX = 1.0
PROVIDER = "openai"
MODEL = "gpt-5"
API_KEY = os.getenv("OPENAI_API_KEY")

@osmosis_rubric
def compute_rubric_score_openai(
    solution_str: str,
    ground_truth: str,
    extra_info: dict,
    **kwargs
) -> float:
    """
    Delegate rubric scoring to OpenAI GPT model.
    """
    model_info = {
        "provider": PROVIDER,
        "model": MODEL,
        "api_key": API_KEY
    }

    result = evaluate_rubric(
        rubric=RUBRIC,
        solution_str=solution_str,
        model_info=model_info,
        ground_truth=ground_truth,
        metadata=extra_info.get("metadata"),
        score_min=SCORE_MIN,
        score_max=SCORE_MAX,
        return_details=False,
    )

    return float(result)

Function Signature

@osmosis_rubric
def my_rubric_function(
    solution_str: str,      # The LLM output to evaluate
    ground_truth: str,      # The expected correct answer
    extra_info: dict,       # Additional context/metadata (required, no default)
    **kwargs                # Future compatibility (REQUIRED)
) -> float:                 # Return score from the rubric
    pass

The `evaluate_rubric` Function

The evaluate_rubric helper function handles the LLM evaluation:

from osmosis_ai import evaluate_rubric

score = evaluate_rubric(
    rubric="Your evaluation criteria here",
    solution_str="The output to evaluate",
    model_info={
        "provider": "openai",
        "model": "gpt-5",
        "api_key": "your-api-key"
    },
    ground_truth="Expected answer",
    metadata={"additional": "context"},
    score_min=0.0,
    score_max=1.0,
    return_details=False
)

Parameters

Parameter	Type	Description
`rubric`	`str`	Natural language description of evaluation criteria
`solution_str`	`str`	The LLM output to evaluate
`model_info`	`dict`	Provider, model, and API key configuration
`ground_truth`	`str`	Expected correct answer or reference
`metadata`	`dict`	Optional additional context
`score_min`	`float`	Minimum score value (default: 0.0)
`score_max`	`float`	Maximum score value (default: 1.0)
`return_details`	`bool`	Whether to return detailed explanation

Supported Providers

OpenAI

from osmosis_ai import evaluate_rubric, osmosis_rubric
import os

@osmosis_rubric
def openai_rubric(
    solution_str: str,
    ground_truth: str,
    extra_info: dict,
    **kwargs
) -> float:
    model_info = {
        "provider": "openai",
        "model": "gpt-5",
        "api_key": os.getenv("OPENAI_API_KEY")
    }

    return evaluate_rubric(
        rubric="Evaluate the solution quality...",
        solution_str=solution_str,
        model_info=model_info,
        ground_truth=ground_truth,
        score_min=0.0,
        score_max=1.0
    )

Anthropic

@osmosis_rubric
def anthropic_rubric(
    solution_str: str,
    ground_truth: str,
    extra_info: dict,
    **kwargs
) -> float:
    model_info = {
        "provider": "anthropic",
        "model": "claude-sonnet-4-5",
        "api_key": os.getenv("ANTHROPIC_API_KEY")
    }

    return evaluate_rubric(
        rubric="Evaluate based on accuracy and clarity...",
        solution_str=solution_str,
        model_info=model_info,
        ground_truth=ground_truth,
        score_min=0.0,
        score_max=1.0
    )

For additional providers (Google Gemini, xAI Grok, OpenRouter, Cerebras), see the API Reference.

Writing Effective Rubrics

Be Specific

# Vague
rubric = "Score the answer quality"

# Specific
rubric = """
Evaluate the solution based on:
1. Correctness: Does it match the ground truth? (50%)
2. Explanation: Is the reasoning clear? (30%)
3. Formatting: Is it well-structured? (20%)

Return a score from 0.0 to 1.0.
"""

Include Scoring Guidelines

rubric = """
Score the code quality from 0.0 to 1.0 based on:

- 1.0: Perfect - Correct, efficient, well-documented
- 0.7-0.9: Good - Correct with minor style issues
- 0.4-0.6: Fair - Works but has problems
- 0.0-0.3: Poor - Incorrect or seriously flawed

Ground truth: {ground_truth}
"""

Provide Examples

rubric = """
Evaluate if the SQL query correctly answers the question.

Examples:
- "SELECT * FROM users WHERE age > 18" for "users over 18" → 1.0
- "SELECT name FROM users WHERE age >= 18" for "users over 18" → 0.8 (missing users exactly 18)
- "SELECT * FROM products" for "users over 18" → 0.0 (wrong table)

Score from 0.0 (completely wrong) to 1.0 (perfect).
"""

Advanced Patterns

Multi-Aspect Evaluation

@osmosis_rubric
def comprehensive_rubric(
    solution_str: str,
    ground_truth: str,
    extra_info: dict,
    **kwargs
) -> float:
    rubric = """
    Evaluate the solution across multiple dimensions:

    1. Factual Accuracy (40%): Is the information correct?
    2. Completeness (30%): Does it address all parts of the question?
    3. Clarity (20%): Is it easy to understand?
    4. Conciseness (10%): Is it appropriately brief?

    Compare against ground truth: {ground_truth}

    Return a weighted average score from 0.0 to 1.0.
    """

    model_info = {
        "provider": "anthropic",
        "model": "claude-sonnet-4-5",
        "api_key": os.getenv("ANTHROPIC_API_KEY")
    }

    return evaluate_rubric(
        rubric=rubric,
        solution_str=solution_str,
        model_info=model_info,
        ground_truth=ground_truth,
        metadata=extra_info.get("metadata"),
        score_min=0.0,
        score_max=1.0
    )

Context-Aware Rubric

@osmosis_rubric
def context_aware_rubric(
    solution_str: str,
    ground_truth: str,
    extra_info: dict,
    **kwargs
) -> float:
    # Extract context from extra_info
    difficulty = extra_info.get("metadata", {}).get("difficulty", "medium")

    rubric = f"""
    Evaluate the solution for a {difficulty} difficulty problem.

    Criteria:
    - Correctness: Must match ground truth logic
    - Approach: Should be appropriate for {difficulty} level
    - Efficiency: Expected to be {get_efficiency_requirement(difficulty)}

    Ground truth: {{ground_truth}}

    Score from 0.0 to 1.0.
    """

    model_info = {
        "provider": "openai",
        "model": "gpt-5",
        "api_key": os.getenv("OPENAI_API_KEY")
    }

    return evaluate_rubric(
        rubric=rubric,
        solution_str=solution_str,
        model_info=model_info,
        ground_truth=ground_truth,
        metadata=extra_info.get("metadata"),
        score_min=0.0,
        score_max=1.0
    )

Getting Detailed Feedback

@osmosis_rubric
def detailed_rubric(
    solution_str: str,
    ground_truth: str,
    extra_info: dict,
    **kwargs
) -> float:
    rubric = "Evaluate the solution quality and provide detailed feedback."

    model_info = {
        "provider": "anthropic",
        "model": "claude-sonnet-4-5",
        "api_key": os.getenv("ANTHROPIC_API_KEY")
    }

    # Get detailed result
    result = evaluate_rubric(
        rubric=rubric,
        solution_str=solution_str,
        model_info=model_info,
        ground_truth=ground_truth,
        score_min=0.0,
        score_max=1.0,
        return_details=True  # Returns dict with score and explanation
    )

    # Log the explanation for debugging
    if isinstance(result, dict):
        print(f"Score: {result['score']}")
        print(f"Reasoning: {result['explanation']}")
        return float(result['score'])

    return float(result)

Error Handling

Always handle errors gracefully:

@osmosis_rubric
def robust_rubric(
    solution_str: str,
    ground_truth: str,
    extra_info: dict,
    **kwargs
) -> float:
    try:
        model_info = {
            "provider": "openai",
            "model": "gpt-5",
            "api_key": os.getenv("OPENAI_API_KEY")
        }

        if not model_info["api_key"]:
            print("Warning: API key not found")
            return 0.0

        result = evaluate_rubric(
            rubric="Evaluate solution quality...",
            solution_str=solution_str,
            model_info=model_info,
            ground_truth=ground_truth,
            score_min=0.0,
            score_max=1.0
        )

        return float(result)

    except Exception as e:
        print(f"Error in rubric evaluation: {e}")
        return 0.0

Best Practices

1. Keep API Keys Secure

import os

# Good - use environment variables
API_KEY = os.getenv("OPENAI_API_KEY")

# Bad - never hardcode keys
API_KEY = "sk-..."  # Don't do this!

2. Choose Appropriate Models

# Example with OpenAI
model = "gpt-5"

# Example with Anthropic
model = "claude-sonnet-4-5"

3. Cache API Calls When Possible

from functools import lru_cache

@lru_cache(maxsize=1000)
def cached_evaluate(solution_str, ground_truth):
    return evaluate_rubric(...)

@osmosis_rubric
def cached_rubric(solution_str: str, ground_truth: str, extra_info: dict, **kwargs) -> float:
    return cached_evaluate(solution_str, ground_truth)

4. Set Appropriate Score Ranges

# For binary outcomes
score_min = 0.0
score_max = 1.0

# For graded responses
score_min = 0.0
score_max = 10.0

# For percentage grades
score_min = 0.0
score_max = 100.0

Testing Locally

Test your rubrics before deployment:

# test_rubrics.py
from reward_rubric.reward_rubric_openai import compute_rubric_score_openai

def test_correct_answer():
    score = compute_rubric_score_openai(
        solution_str="The answer is 42",
        ground_truth="42",
        extra_info={}
    )
    print(f"Correct answer score: {score}")
    assert 0.8 <= score <= 1.0

def test_incorrect_answer():
    score = compute_rubric_score_openai(
        solution_str="The answer is 100",
        ground_truth="42",
        extra_info={}
    )
    print(f"Incorrect answer score: {score}")
    assert 0.0 <= score <= 0.3

if __name__ == "__main__":
    test_correct_answer()
    test_incorrect_answer()
    print("Tests passed!")

Next Steps

Setup Guide

Complete setup walkthrough

Best Practices

Tips and troubleshooting

Python SDK

Full API reference

Example Repo

See complete examples

​Basic Example

​Function Signature

​The evaluate_rubric Function

​Parameters

​Supported Providers

​OpenAI

​Anthropic

​Writing Effective Rubrics

​Be Specific

​Include Scoring Guidelines

​Provide Examples

​Advanced Patterns

​Multi-Aspect Evaluation

​Context-Aware Rubric

​Getting Detailed Feedback

​Error Handling

​Best Practices

​1. Keep API Keys Secure

​2. Choose Appropriate Models

​3. Cache API Calls When Possible

​4. Set Appropriate Score Ranges

​Testing Locally

​Next Steps

Setup Guide

Best Practices

Python SDK

Example Repo

Basic Example

Function Signature

The `evaluate_rubric` Function

Parameters

Supported Providers

OpenAI

Anthropic

Writing Effective Rubrics

Be Specific

Include Scoring Guidelines

Provide Examples

Advanced Patterns

Multi-Aspect Evaluation

Context-Aware Rubric

Getting Detailed Feedback

Error Handling

Best Practices

1. Keep API Keys Secure

2. Choose Appropriate Models

3. Cache API Calls When Possible

4. Set Appropriate Score Ranges

Testing Locally

Next Steps