Use Lighthouse for performance budgets

Jun 14, 2019 — Updated Apr 3, 2020

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Katie Hempenius

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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.

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

View the Results #

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

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