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Lighthouse Scores

How is the Performance score calculated?

➡️ Please read Lighthouse Performance Scoring at web.dev.

How is the PWA (Progressive Web App) score calculated?

The PWA category doesn't get a 0-100 score, but instead is evaluated in 3 separate groups (Fast and reliable, Installable, and PWA Optimized). In order to satisfy each grouping (and get the associated badge), every audit within the group must be passing.

Lighthouse PWA badge - states

Note on https redirects: some metrics in this category have issues with https redirects because of TLS-handshake errors. More specifically you will run into this when using the simplehttp2server npm package. Subsequent metrics will fail after the https redirects (see #1217, #5910).

How is the Best Practices score calculated?

All audits in the Best Practices category are equally weighted. Therefore, implementing each audit correctly will increase your overall score by ~6 points.

How is the SEO score calculated?

All audits in the SEO category are equally weighted, with the exception ofStructured Data, which is an unscored manual audit. Therefore, implementing each audit correctly will increase your overall score by ~8 points.

How is the accessibility score calculated?

The accessibility score is a weighted average. The specific weights for v7 are as follows:

(See the v6 scoring explanation)

audit id weight
aria-allowed-attr 4.1%
aria-hidden-body 4.1%
aria-required-attr 4.1%
aria-required-children 4.1%
aria-required-parent 4.1%
aria-roles 4.1%
aria-valid-attr-value 4.1%
aria-valid-attr 4.1%
button-name 4.1%
duplicate-id-aria 4.1%
image-alt 4.1%
input-image-alt 4.1%
label 4.1%
meta-refresh 4.1%
meta-viewport 4.1%
video-caption 4.1%
accesskeys 1.2%
aria-command-name 1.2%
aria-hidden-focus 1.2%
aria-input-field-name 1.2%
aria-meter-name 1.2%
aria-progressbar-name 1.2%
aria-toggle-field-name 1.2%
aria-tooltip-name 1.2%
aria-treeitem-name 1.2%
bypass 1.2%
color-contrast 1.2%
definition-list 1.2%
dlitem 1.2%
document-title 1.2%
duplicate-id-active 1.2%
frame-title 1.2%
html-has-lang 1.2%
html-lang-valid 1.2%
link-name 1.2%
list 1.2%
listitem 1.2%
object-alt 1.2%
tabindex 1.2%
td-headers-attr 1.2%
th-has-data-cells 1.2%
valid-lang 1.2%
form-field-multiple-labels 0.8%
heading-order 0.8%

Each audit is a pass/fail, meaning there is no room for partial points for getting an audit half-right. For example, that means if half your buttons have screenreader friendly names, and half do not, you don't get "half" of the weighted average - you get a 0 because it needs to be implemented correctly throughout the page.