> ## Documentation Index > Fetch the complete documentation index at: https://docs.halios.ai/llms.txt > Use this file to discover all available pages before exploring further. # Evaluation concepts > Key terms and mental models used in Halios evaluations. The core evaluation flow in Halios follows a simple progression: ```text theme={null} Scenario → fresh trials → traces → checks → results ``` A **scenario** is the reusable test. A **trace** is the execution evidence from one trial. Running the scenario again produces a fresh trace against the current version of your agent. *** ## Core terms ### Scenario The reusable test situation you want to evaluate. It defines the initial user goal, persona, constraints, and multi-turn conversation arc. ### Trial One fresh execution generated from a scenario. Instead of replaying a saved transcript, Halios simulates a live user interaction with your agent for each trial. ### Trace The execution evidence emitted by your agent during a trial. Contains the full conversational turn history, model calls, tool arguments, retrieval context, and latency metrics. ### Check One specific invariant you want to verify about your agent's behavior (e.g. answer groundedness, regex format match, policy compliance, or tool argument schema). ### Eval suite The collection of scenarios, checks, and configuration defined for an agent or workflow (stored in your repository under `.halios/`). ### Run One complete execution pass of an eval suite against the current agent implementation, recording trial traces, check evaluations, and pass rates. ### pass\@k Repeating the same scenario $k$ times (e.g. 3 or 5 trials) to measure consistency. A scenario passes only if all $k$ trials succeed, ensuring that passing was not just random chance. *** Get started with your coding agent in minutes. Command reference for automation and CI pipelines.