Accessibility Performance Measurements

Accessibility support in Chromium can be expensive, so we have some performance tests to help catch regressions and encourage improving performance over time.

As background material, read up on Telemetry, Chromium's performance testing framework.

The metrics for accessibility are defined here:


They measure the time spent in three key parts of accessibility code in Chrome, wherever you see SCOPED_TRACE. If there‘s any nontrivial code that you think is being called that isn’t covered now, the first step would be to add a new SCOPED_TRACE, then update this metric to start tracking it.


The stories are defined here:


A story is a url to load and other actions to take on that page. The accessibility stories are also configured to run with accessibility enabled via the command-line flag.

If there‘s a particular web page that seems slow and you’d like to start tracking its performance, the first step would be to try adding a new story here.

Here's an example command line to run all of the accessibility stories locally using the currently installed Canary browser:

tools/perf/run_benchmark system_health.common_desktop --story-filter="accessibility.*" --browser canary

See the documentation or command-line help for tools/perf/run_benchmark for more command-line arguments.

Here's an example command line to run to capture the web page replay for all accessibility stories, if you add a new story or update an existing one:

tools/perf/record_wpr desktop_system_health_story_set --story-filter="accessibility.*" --browser canary

Running this will upload the web page replay data captured and modify this file, which should be submitted as part of your changelist:


For more information, see Record a page set.

Blink Perf

In addition, we have Blink perf tests here. These are microbenchmarks intended to track the performance of a small function or operation in isolation. You can find these tests here:



The results can be found at Because that site displays graphs, we also maintain a command-line script (Google-internal only) as a more accessible alternative way to examine the same data via the command line.

To get the script:

git clone sso://user/dmazzoni/chrome-accessibility-site and then run:

./ perf