Use Lighthouse for performance budgets

Lighthouse now supports performance budgets. This feature, known as LightWallet, can be set up in under five minutes and provides feedback on performance metrics and the size and quantity of page resources.

{% Aside 'important' %} While Lighthouse is an excellent tool for identifying performance improvement opportunities, it can't be stressed enough that Lighthouse is a tool that relies on lab data. While lab data is an integral part of any performance improvement effort, comparing and contrasting that data with field data collected from your website's actual users is key. Doing so will help you understand how the changes you make to your website affect real users. {% endAside %}

Install Lighthouse

LightWallet is available in the command line version of Lighthouse v5+.

To get started, install Lighthouse:

npm install -g lighthouse

Create a Budget

Create a file named budget.json. In this file add the following JSON:

[
  {
    "path": "/*",
    "timings": [
      {
        "metric": "interactive",
        "budget": 3000
      },
      {
        "metric": "first-meaningful-paint",
        "budget": 1000
      }
    ],
    "resourceSizes": [
      {
        "resourceType": "script",
        "budget": 125
      },
      {
        "resourceType": "total",
        "budget": 300
      }
    ],
    "resourceCounts": [
      {
        "resourceType": "third-party",
        "budget": 10
      }
    ]
  }
]

This example budget.json file sets five separate budgets:

• A budget of 3000ms for Time to Interactive.
• A budget of 1000ms for First Meaningful Paint
• A budget of 125 KB for the total amount of JavaScript on the page.
• A budget of 300 KB for the overall size of the page.
• A budget of 10 requests for the number of requests made to third-party origins.

For a complete list of supported performance metrics and resource types, refer to the Performance Budgets section of the Lighthouse docs.

Run Lighthouse

Run Lighthouse using the --budget-path flag. This flag tells Lighthouse the location of your budget file.

lighthouse https://example.com --budget-path=./budget.json

{% Aside %} Note: A budget file does not have to be named budget.json. {% endAside %}

View the Results

If LightWallet has been configured correctly, the Lighthouse report will contain a Budgets section within the Performance category.

{% Img src="image/admin/FdUeI8rKZtJB3Ol624S3.png", alt="'Budgets' section of the Lighthouse report", width="800", height="289" %}

In the JSON version of the Lighthouse report, Lightwallet results can be found within the audit findings for the performance-budget audit.