Custom extractors

Create your own extractors to pull exactly what you need from agent trajectories.

While built-in extractors cover common cases, custom extractors let you implement specialized extraction logic for your specific use case.

Why Custom Extractors?

Use custom extractors when you need to:

• Extract structured data: Parse JSON fields from agent responses
• Filter specific patterns: Extract code blocks, URLs, or formatted content
• Combine data sources: Merge information from multiple messages or memory blocks
• Count occurrences: Track how many times something happened
• Complex logic: Implement domain-specific extraction

Basic Structure

from letta_evals.decorators import extractor
from letta_client import LettaMessageUnion
from typing import List

@extractor
def my_extractor(trajectory: List[List[LettaMessageUnion]], config: dict) -> str:
    """Extract custom content from trajectory."""
    # Your extraction logic here
    return extracted_text

Example: Extract Memory Insert

from letta_evals.decorators import extractor

@extractor
def memory_insert_args(trajectory, config):
    """Extract arguments from memory_insert tool calls."""
    for turn in trajectory:
        for message in turn:
            if hasattr(message, 'tool_call') and message.tool_call:
                if message.tool_call.name == "memory_insert":
                    return str(message.tool_call.arguments)
    return ""

Registration

Custom extractors are automatically registered when you import them in your suite’s setup script or custom evaluators file.

Next Steps

• Built-in Extractors - Available extractors
• Extractors Concept - Understanding extractors