---
title: Give the agent skills
description: Place a skill where the harness loads it, and check the agent used it.
---
> ## Documentation Index
> Fetch the complete documentation index at: https://docs.reeval.ai/llms.txt
> Use this file to discover all available pages before exploring further.

You place a skill on an environment so the harness can load it during an attempt. Each entry in `skills` comes from the `skill` helper. For more information about measuring whether a skill helped, see [Measure lift against a baseline](/results/compare/lift).

## Add a skill

In the `evals/environments.ts` file, place a skill from a host directory with `skill.local()`:

```ts title="evals/environments.ts"
import { defineEnvironment } from '{{ pkg }}'

export const math = defineEnvironment('math', ({ directory, skill }) => ({
  files: directory('./project'),
  skills: [skill.local('./skills/jsdoc')],
}))
```

Pass `math` as an evaluation's `environment`, as [Environments](/configuration/environments#define-and-use-an-environment) shows. To compare the environment with and without the skill, see [Measure lift against a baseline](/results/compare/lift).

A skill directory holds a `SKILL.md` file. The frontmatter `name` is kebab-case, and `description` is required. When the frontmatter omits `name`, reeval uses the directory name. A `name` other than kebab-case, or a missing `description`, fails the attempt. Quote a frontmatter value that contains `": "`.

## Use another source

Place a skill from a repository with [`skill.git`](/reference/environment-helpers#skillgit), from skills.sh with [`skill.registry`](/reference/environment-helpers#skillregistry), from an npm package with [`skill.npm`](/reference/environment-helpers#skillnpm), or from a name, a description, and its content with [`skill.inline`](/reference/environment-helpers#skillinline). For a runnable project, see [`with-skill-sources`](https://github.com/invertase/reeval/tree/main/examples/with-skill-sources).

## Check the agent used the skill

`toHaveCalledSkill` fails the attempt when the agent never loads that skill. It passes when a tool named `skill`, `Skill`, or `load_skill` loads the name, or when the agent reads a file under `skills/<name>/`.

To check every turn of the attempt, pass `c` after the final `c.send()` call. To check one turn, pass the turn returned by `c.send()`:

```ts title="with-skill.eval.ts"
const turn = await c.send('Add a multiply(a, b) function to src/math.js.')

expect(turn).toHaveCalledSkill('jsdoc')
```

For a runnable project, see [`with-skill`](https://github.com/invertase/reeval/tree/main/examples/with-skill).

For more information about this matcher, see [toHaveCalledSkill](/reference/matchers#tohavecalledskill).