# Fitness Function

## Definition
A metric used in the Knock-out multi-agent pattern to evaluate how well each agent performs a task. The function determines which agents survive and which are eliminated. It can be deterministic (e.g., unit tests, exact match) or LLM-based (e.g., quality scoring).

## Role in Multi-Agent Knock-out
- Evaluates output of each agent
- Produces a score or boolean pass/fail
- Used to rank agents and identify worst performers
- Guides the selection/elimination process

## Key Properties
- Must be fast — if humans need to verify all branches, the process is too slow
- Should be deterministic where possible (unit tests over LLM judgment)
- Can be composite: multiple criteria combined into single score
- Is where "Evals" come in (critical infrastructure for agent development)

## Examples
- Unit test pass rate
- Exact string match against expected output
- LLM-based quality scoring (with rubric)
- Latency or token cost as secondary factors

## Related Concepts
- [[Genetic Algorithms]]
- [[Multi-Agent Knock-out]]
- [[Validator]]
- [[Evals]]