> ## Documentation Index > Fetch the complete documentation index at: https://docs.stet.sh/llms.txt > Use this file to discover all available pages before exploring further. # How Stet works > From accepted repository work to a scoped Trial Result Stet is a measurement function for AI coding behavior. The coding agent makes a bounded change; Stet evaluates that change against replayable repository work and records what the evidence supports. The Stet evaluation loop: real merged work becomes replayable tasks, baseline and candidate are evaluated with tests and graders, and a Trial Result returns a bounded decision. ## 1. Accepted work becomes a task corpus Stet starts from real merged repository work rather than synthetic benchmark prompts. Each selected task keeps: * the repository snapshot before the change; * a prompt describing the work; * the tests or validation signal that judged success; and * the original shipped change hidden from the agent under test. The retained slice is a declared part of the evidence. Your agent should inspect CI and history, ask what work matters, and explain coverage and gaps before a large evaluation. ## 2. Replay holds the world steady For the default path, Stet launches an isolated container with the task snapshot and prompt. The agent can inspect files, edit code, and run commands as usual, but it does not see the hidden gold patch or hidden judging tests. Supported local runs can use an explicitly selected worktree backend; that is still a local mode, not Docker-equivalent isolation. Treat worktree-backed evidence as inspect-only by default. It should support a decision only when the Trial Result explicitly says that the evidence is decision-grade; use Docker-backed replay otherwise. ## 3. Baseline and candidate are matched Stet declares the behavior being tested and runs a baseline and candidate against the same task slice. Keep unrelated model, instruction, tool, and environment settings stable when the goal is to attribute an observed difference to one lever. The coding agent proposes and applies the change. Stet is the evaluator: it applies the produced patch, runs the declared checks, and records evidence. ## 4. Tests come first; graders add quality Tests provide correctness signal. Graders can then assess dimensions such as equivalence, clarity, simplicity, coherence, intentionality, robustness, instruction adherence, scope discipline, and diff minimality. A patch can pass tests and still be broader or harder to review than the task called for. The grader model may be separate from the model under test. What matters is that the rubric and coverage are declared and that missing or failed grader evidence stays visible. ## 5. Stet writes a Trial Result The result names the task corpus, treatments, tests and graders, per-dimension observations, evidence quality, lifecycle posture, and next action. Read those fields together on [Read a Trial Result](/concepts/trial-result); a single score is not the decision.