---
title: "How to use options | Grafana k6 documentation"
description: "How to set options in different places (with examples), how to override options, and how to access the value of an option as the test runs."
---

# How to use options

k6 provides multiple places to set options:

- In CLI flags
- In environment variables
- In the script `options` object
- In a configuration file

Most likely, your use case will determine where you want to set the particular options for a particular test. You can also access option values as your test runs.

## Order of precedence

You can set options in multiple places. If there are conflicts, k6 uses the option from the place with the highest *order of precedence*.

1. First, k6 uses the option’s default value.
2. Next, k6 uses the options set in a configuration file via the `--config` flag.
3. Then, k6 uses the script value (if set).
4. After, k6 uses the environment variable (if set).
5. Finally, k6 takes the value from the CLI flag (if set).

That is, **command-line flags have the highest order of precedence**.

## Where to set options

Sometimes, how you set options is a matter of personal preference. Other times, the context of your test dictates the most sensible place to put your options.

- **Options in the script to version control and keep tests tidy**
  
  The script `options` object is generally the best place to put your options. This provides automatic version control, allows for easy reuse, and lets you modularize your script.
- **CLI flags to set options on the fly**
  
  When you want to run a quick test, command-line flags are convenient.
  
  You can also use command-line flags to override files in your script (as determined by the [order of precedence](#order-of-precedence)). For example, if your script file sets the test duration at 60 seconds, you could use a CLI flag to run a one-time shorter test. With a flag like `--duration 30s`, the test would be half as long but otherwise identical.
- **Environment variables to set options from your build chain**
  
  For example, you could derive the option from a variable in your Docker container definition, CI UI, or vault—wherever you declare environment variables.
  
  The [block hostnames](/docs/k6/latest/using-k6/k6-options/reference/#block-hostnames) option is an example of an option that works well with environment variables.

## Examples of setting options

The following JS snippets show some examples of how you can set options.

### Set options in the script

JavaScript ![Copy code to clipboard](/media/images/icons/icon-copy-small-2.svg) Copy

```javascript
import http from 'k6/http';

export const options = {
  hosts: { 'test.k6.io': '1.2.3.4' },
  stages: [
    { duration: '1m', target: 10 },
    { duration: '1m', target: 20 },
    { duration: '1m', target: 0 },
  ],
  thresholds: { http_req_duration: ['avg<100', 'p(95)<200'] },
  noConnectionReuse: true,
  userAgent: 'MyK6UserAgentString/1.0',
};

export default function () {
  http.get('http://test.k6.io/');
}
```

### Set options with environment variables

You can also set the options from the previous example through environment variables and command-line flags:

Bash windows powershell

![Copy code to clipboard](/media/images/icons/icon-copy-small-2.svg) Copy

Bash ![Copy code to clipboard](/media/images/icons/icon-copy-small-2.svg) Copy

```bash
K6_NO_CONNECTION_REUSE=true K6_USER_AGENT="MyK6UserAgentString/1.0" k6 run script.js

k6 run --no-connection-reuse --user-agent "MyK6UserAgentString/1.0" script.js
```

windows ![Copy code to clipboard](/media/images/icons/icon-copy-small-2.svg) Copy

```windows
set "K6_NO_CONNECTION_REUSE=true" && set "K6_USER_AGENT=MyK6UserAgentString/1.0" && k6 run script.js

k6 run --no-connection-reuse --user-agent "MyK6UserAgentString/1.0" script.js
```

powershell ![Copy code to clipboard](/media/images/icons/icon-copy-small-2.svg) Copy

```powershell
$env:K6_NO_CONNECTION_REUSE=true; $env:K6_USER_AGENT="MyK6UserAgentString/1.0"; k6 run script.js

k6 run --no-connection-reuse --user-agent "MyK6UserAgentString/1.0" script.js
```

### Set options from k6 variables

With the `--env` flag, you can use the CLI to define k6 variables. Then, you can use the variable to dynamically define an option’s value in the script file.

For example, you could define a variable for your user agent like this:

Bash ![Copy code to clipboard](/media/images/icons/icon-copy-small-2.svg) Copy

```bash
k6 run script.js --env MY_USER_AGENT="hello"
```

Then, your script could then set the `userAgent` option based on the variable’s value. This allows for quick configuration.

JavaScript ![Copy code to clipboard](/media/images/icons/icon-copy-small-2.svg) Copy

```javascript
import http from 'k6/http';

export const options = {
  userAgent: __ENV.MY_USER_AGENT,
};

export default function () {
  http.get('http://test.k6.io/');
}
```

> **Note**: Though this method uses the `--env` flag, this is not the same as using an environment variable. For an explanation, refer to the [environment variables document](/docs/k6/latest/using-k6/environment-variables/).

### Set options with the –config flag

k6 includes a [default configuration file](/docs/k6/latest/using-k6/k6-options/reference/#config) that you can edit, or you can create a new file and then use a CLI flag to point to that file. If you use it, the options take the *second lowest order of precedence* (after defaults). If you set options anywhere else, they will override the `--config` flag options.

Use the `--config` flag to declare the file path to your options.

Bash ![Copy code to clipboard](/media/images/icons/icon-copy-small-2.svg) Copy

```bash
k6 run --config options.json script.js
```

This command would set test options according to the values in the `options.json` file.

JSON ![Copy code to clipboard](/media/images/icons/icon-copy-small-2.svg) Copy

```json
{
  "hosts": {
    "test.k6.io": "1.2.3.4"
  },
  "stages": [
    {
      "duration": "1m",
      "target": 10
    },
    {
      "duration": "1m",
      "target": 30
    },
    {
      "duration": "1m",
      "target": 0
    }
  ],
  "thresholds": {
    "http_req_duration": ["avg<100", "p(95)<200"]
  },
  "noConnectionReuse": true,
  "userAgent": "MyK6UserAgentString/1.0"
}
```

For an alternative way to separate configuration from logic, you can use the `JSON.parse()` method in your script file:

JavaScript ![Copy code to clipboard](/media/images/icons/icon-copy-small-2.svg) Copy

```javascript
// load test config, used to populate exported options object:
const testConfig = JSON.parse(open('./config/test.json'));
// combine the above with options set directly:
export const options = testConfig;
```

## Get an option value from the script

The `k6/execution` API provides a [test.options](/docs/k6/latest/javascript-api/k6-execution/#test) object. With `test.options`, you can access the consolidated and derived options of your script as the test runs.

A common use of this feature is to log the value of a tag, but there are many possibilities. For example, this script accesses the value of the test’s current stage:

JavaScript ![Copy code to clipboard](/media/images/icons/icon-copy-small-2.svg) Copy

```javascript
import exec from 'k6/execution';

export const options = {
  stages: [
    { duration: '5s', target: 100 },
    { duration: '5s', target: 50 },
  ],
};

export default function () {
  console.log(exec.test.options.scenarios.default.stages[0].target); // 100
}
```