Lighthouse Best Practices Cheat Sheet

Checklist of general practices to improve the overall code health of your web app

Monday, February 7, 2022

best practice

TL;DR

Use Lighthouse to check if your website is following the list of best practices. You will see the same exact information in the Best Practices report.

Here some of the best practices audits to improve the code health of your web page. To learn more, check this page where I based the categorization.


General best practices

Specifying a doctype prevents the browser from switching to quirks-mode.

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Errors logged to the console indicate unresolved problems. They can come from network request failures and other browser concerns.

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Image display dimensions should match natural aspect ratio.

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A character encoding declaration is required. It can be done with a <meta> tag in the first 1024 bytes of the HTML or in the Content-Type HTTP response header.

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Preload optional fonts so first-time visitors may use them.

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The unload event does not fire reliably and listening for it can prevent browser optimizations like the Back-Forward Cache. Consider using the pagehide or visibilitychange events instead.

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Make your page secure

All sites should be protected with HTTPS, even ones that don't handle sensitive data. This includes avoiding mixed content, where some resources are loaded over HTTP despite the initial request being served over HTTPS. HTTPS prevents intruders from tampering with or passively listening in on the communications between your app and your users, and is a prerequisite for HTTP/2 and many new web platform APIs.

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All front-end JavaScript libraries detected on the page.

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A strong Content Security Policy (CSP) significantly reduces the risk of cross-site scripting (XSS) attacks.

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Add rel="noopener" or rel="noreferrer" to any external links to improve performance and prevent security vulnerabilities.

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Some third-party scripts may contain known security vulnerabilities that are easily identified and exploited by attackers.

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Create a good user experience

Image natural dimensions should be proportional to the display size and the pixel ratio to maximize image clarity.

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Users are mistrustful of or confused by sites that request their location without context. Consider tying the request to a user action instead.

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Users are mistrustful of or confused by sites that request to send notifications without context. Consider tying the request to user gestures instead.

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Preventing password pasting undermines good security policy.

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Avoid deprecated technologies

Application Cache is deprecated.

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Deprecated APIs will eventually be removed from the browser.

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Diagnostics audits

All front-end JavaScript libraries detected on the page.

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Issues logged to the Issues panel in Chrome Devtools indicate unresolved problems. They can come from network request failures, insufficient security controls, and other browser concerns. Open up the Issues panel in Chrome DevTools for more details on each issue.


Source maps translate minified code to the original source code. This helps developers debug in production. In addition, Lighthouse is able to provide further insights. Consider deploying source maps to take advantage of these benefits.

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