---
title: 'Parameters'
---

Parameters are a set of static, named metadata about a story, typically used to control the behavior of Storybook features and addons.

For example, let’s customize the backgrounds addon via a parameter. We’ll use `parameters.backgrounds` to define which backgrounds appear in the backgrounds toolbar when a story is selected.

## Story parameters

We can set a parameter for a single story with the `parameters` key on a CSF export:

```js
// Button.story.js

export const Primary = Template.bind({});
Primary.args = {
  primary: true,
  label: 'Button',
};
Primary.parameters = {
  backgrounds: {
    values: [
      { name: 'red', value: '#f00' },
      { name: 'green', value: '#0f0' },
    ],
  },
};
```

## Component parameters

We can set the parameters for all stories of a component using the `parameters` key on the default CSF export:

```js
// Button.story.js

import Button from './';

export default {
  title: 'Button',
  component: Button,
  parameters: {
    backgrounds: {
      values: [
        { name: 'red', value: '#f00' },
        { name: 'green', value: '#0f0' },
      ],
    },
  },
};
```

## Global parameters

We can also set the parameters for **all stories** via the `parameters` export of your [`.storybook/preview.js`](../configure/overview.md#configure-story-rendering) file (this is the file where you configure all stories):

```js
// .storybook/preview.js

export const parameters = {
  backgrounds: {
    values: [
      { name: 'red', value: '#f00' },
      { name: 'green', value: '#0f0' },
    ],
  },
};
```

Setting a global parameter is a common way to configure addons. With backgrounds, you configure the list of backgrounds that every story can render in.

## Rules of parameter inheritance

The way the global, component and story parameters are combined is:

- More specific parameters take precedence (so a story parameter overwrites a component parameter which overwrites a global parameter).
- Parameters are **merged** so keys are only ever overwritten, never dropped.

The merging of parameters is important. It means it is possible to override a single specific sub-parameter on a per-story basis but still retain the majority of the parameters defined globally.

If you are defining an API that relies on parameters (e..g an [**addon**](../api/addons.md)) it is a good idea to take this behavior into account.
