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Creating a Basic Online Evaluator

This example walks through setting up a simple online evaluator that checks if an LLM response contains specific keywords, useful for content moderation or topic classification.
1

1. Navigate to Evaluators Page

From your Laminar dashboard, go to the Evaluators page and click “New Evaluator” to start creating your custom evaluation logic.
2

2. Define Your Evaluator Function

Create a Python function that analyzes the LLM output. This example checks for the presence of specific keywords and assigns a score based on relevance.Important: Online evaluator functions must return a single number as the score. The system automatically attaches this score to the span for monitoring and analysis.
def keyword_checker(input):
    """
    Evaluator that checks if the output contains relevant keywords
    Returns a score from 0 to 1 based on keyword presence
    Note: Must return a single number as the score
    """
    def extract_text(data):
        if isinstance(data, str):
            return data
        if isinstance(data, dict) and 'content' in data:
            content = data['content']
            if isinstance(content, str):
                return content
            if isinstance(content, list) and content:
                first = content[0]
                return first.get('text', str(first)) if isinstance(first, dict) else str(first)
        return str(data)
    
    text_content = extract_text(input)
    important_keywords = ['solution', 'help', 'recommend', 'suggest']
    
    keyword_count = sum(1 for keyword in important_keywords if keyword in text_content.lower())
    return min(keyword_count / len(important_keywords), 1.0)
Create evaluator function
3

3. Test Your Evaluator

Use the test interface to verify your evaluator works correctly with sample inputs.
{
    "content": [
        {"text": "Let me suggest a helpful approach"}
    ]
}
Test evaluator
4

4. Register to Span Path

Navigate to your traces, find a span representing the LLM call you want to evaluate, and register your evaluator to that specific span path by clicking evaluators on span view.
Register to span path
5

5. Verify Automatic Execution

After registration, new spans on that path will automatically trigger your evaluator. Check the span details to see the attached evaluation scores.
Verify execution - evaluator scores displayed in span