> ## Documentation Index
> Fetch the complete documentation index at: https://langwatch.ai/docs/llms.txt
> Use this file to discover all available pages before exploring further.
# Scenario tests and evaluations
> What Langy produces when it tests your agent: Scenario multi-turn simulation tests and evaluations, written and run through the langwatch CLI.
Both are real artifacts, not drafts: Langy writes and runs them through the `langwatch` CLI, so what comes back lives in your project like any test or evaluator you wrote by hand. Which one it picks depends on what the question needs to prove; see the table below.
**Also check:** [Ask Langy](/docs/langy/chat) (how you request a test), [Pull requests](/docs/langy/pull-requests) (the tests it wrote run in your CI), [Agent Simulations](/docs/agent-simulations/introduction) and [Evaluations](/docs/evaluations/overview) (the product surfaces these land in).
## Scenario simulation tests
A Scenario test is a multi-turn simulation. A simulated user drives your agent across a full conversation, probing it the way a real user would, and a judge scores the transcript against the criteria you set.
This is how Langy catches behavior that a single-turn check misses: an agent that holds the line for one message but drifts by turn 15.
Langy writes and runs these with:
```bash theme={null}
langwatch scenario create
langwatch scenario run
```
The runs land in the Simulations surface, where you can filter, group, and open any run.
Open a run to see the judge's verdict and its reasoning against your criteria.
When a run fails, the detail includes the bug log so you can see exactly where the agent broke.
Read more in the Agent Simulations docs: [Introduction](/docs/agent-simulations/introduction), [Getting started](/docs/agent-simulations/getting-started), [Red teaming](/docs/agent-simulations/red-teaming), and [Voice agents](/docs/agent-simulations/voice-agents).
## Evaluations
An evaluation scores a run against a criterion: answer correctness, a custom rule, an LLM judge, a pairwise comparison. Langy writes evaluators and runs experiments and monitors with the CLI:
```bash theme={null}
langwatch evaluator create
langwatch experiment run
langwatch monitor create
```
Use each for a different job:
* `langwatch experiment run` scores an offline or batch run, for comparing two models or two prompts. See [Experiments](/docs/evaluations/experiments/overview) and [running evals in CI/CD](/docs/evaluations/experiments/ci-cd).
* `langwatch monitor create` sets up an online evaluation that scores live production traffic. See [Online evaluation](/docs/evaluations/online-evaluation/overview).
* `langwatch evaluator create` defines the evaluator both of the above use. See [Evaluators](/docs/evaluations/evaluators/overview).
## Which one Langy picks
Langy picks based on what your question needs to prove:
| You want to check | Langy writes |
| ----------------------------------------------- | -------------------------- |
| The agent handles a full conversation correctly | A Scenario simulation test |
| One run scores well on a criterion | An evaluation |
| Live traffic stays within a criterion | An online monitor |
| Two models or prompts, head to head | An experiment |
You can also name the one you want in the [chat](/docs/langy/chat): "write a Scenario test that..." or "set up an evaluator for...".