Chrome’s Lighthouse provides an invaluable tool for identifying accessibility concerns. However, people often misunderstand what the given score means.
Far too many times, I’ve seen people confidently claim that their website is accessible because they’re scoring 100% for accessibility in Lighthouse. This is not what the metric is telling us; it’s really important that we understand this.
Lighthouse, like other accessibility tools, is limited by what can be effectively tested through automation. Things like meaningful link text, resizable text and clear keyboard navigation require manual, real user testing.
Robson Square
The Robson Square steps in Vancouver architecturally look beautiful and at first glance look accessible. There’s a ramp that zig-zags up the incline and handrails at the edges. However, looks can be deceiving. These steps present many accessibility issues:
- The ramp is too steep: the excessive incline is dangerous for most wheelchair users.
- There are lots of trip hazards: the monochromatic concrete design makes it hard for visually impaired people to differentiate between the steps and ramp.
- There’s a lack of safety railings: this creates a risk of falling for many people.
At the time of construction, the steps were built to meet the accessibility requirements of the day. If Lighthouse could assess real world architecture, they’d have scored 100.
Lighthouse
Tools like Lighthouse aren’t bad. They’re useful for catching technical accessibility issues. However, we need to remember who we are checking accessibility for.
Accessibility issues are human-centred problems. There’s only so far automation can go before we need to do real-person testing. Lighthouse can’t replicate the lived experience.
Lighthouse is at its most useful when the returned score is below 100. Not because this is a desired result, but because this is when it highlights possible issues worth investigating.
A score of 100 also doesn’t imply that the potential issues Lighthouse can test for aren’t still problematic. You may have provided alt text for all images, but whether that alt text is useful is another matter.
It is possible to get a 100% accessible Lighthouse score for the most inaccessible site.
We need to recognise the limitations of Lighthouse and other automated testing tools for accessibility. Getting a perfect Lighthouse score is just the first step towards building an accessible Web.