Crossbench is a cross-browser/cross-benchmark runner to extract performance numbers.

Supported Browsers: Chrome/Chromium, Firefox, Safari and Edge.

Supported OS: macOS, linux and windows.

Basic usage:

Chromium Devs (with a full chromium checkout)

Use the ./ script to run benchmarks (requires chrome's vpython3)

Standalone installation

Use the “poetry” package manager, see the development section.

Run the latest speedometer benchmark 20 times with the system default browser (chrome-stable):

# Run chrome-stable by default:
./ speedometer --repeat=20

# Compare browsers on jetstream:
./ jetstream --browser=chrome-stable --browser=chrome-m90 --browser=$PATH

Profile individual line items (with pprof on linux):

./ speedometer --probe=profiling --separate

Use a custom chrome build and only run a subset of the stories:

./ speedometer --browser=$PATH --probe=profiling --story='Ember.*'

Profile a website for 17 seconds on Chrome M100 (auto-downloading on macOS and linux):

./ loading --browser=chrome-m100 --probe=profiling,17s

Main Components


Crossbench supports running benchmarks on one or multiple browser configurations. The main implementation uses selenium for maximum system independence.

You can specify a browser with --browser=<name>. You can repeat the --browser argument to run multiple browser. If you need custom flags for multiple browsers use --browser-config (or pass simple flags after -- to the browser).

./ speedometer --browser=$BROWSER -- --enable-field-trial-config 

Browser Config File

For more complex scenarios you can use a browser.config.hjson file. It allows you to specify multiple browser and multiple flag configurations in a single file and produce performance numbers with a single invocation.

./ speedometer --browser-config=config.hjson

The example file lists and explains all configuration details.


Probes define a way to extract arbitrary (performance) numbers from a host or running browser. This can reach from running simple JS-snippets to extract page-specific numbers to system-wide profiling.

Multiple probes can be added with repeated --probe=XXX options. You can use the describe probes subcommand to list all probes:

# List all probes:
./ describe probes

# List help for an individual probe:
./ describe probe v8.log

Inline Probe Config

Some probes can be configured, either with inline json when using --probe or in a separate --probe-config hjson file. Use the describe command to list all options.

# Get probe config details:
./ describe probe v8.log

# Use inline hjson to configure a probe:
./ speedometer --probe='v8.log{prof:true}'

Probe Config File

For complex probe setups you can use --probe-config=<file>. The example file lists and explains all configuration details. For the specific probe configuration properties consult the describe command.


Use the describe command to list all benchmark details:

# List all benchmark info:
./ describe benchmarks

# List an individual benchmark info:
./ describe benchmark speedometer_2.1

# List a benchmark's command line options:
./ speedometer_2.1 --help


Stories define sequences of browser interactions. This can be simply loading a URL and waiting for a given period of time, or in more complex scenarios, actively interact with a page and navigate multiple times.

Use --help or describe to list all stories for a benchmark:

./ speedometer --help

Use --stories to list individual story names, or use regular expression as filter.

./ speedometer --browser=$BROWSER --stories='VanillaJS.*'



This project uses poetry deps and package scripts to setup the correct environment for testing and debugging.

pip3 install poetry

Check that you have poetry on your path and make sure you have the right $PATH settings.

poetry --help || echo "Please update your \$PATH to include poetry bin location";
# Depending on your setup, add one of the following to your $PATH:
echo "`python3 -m site --user-base`/bin";
python3 -c "import sysconfig; print(sysconfig.get_path('scripts'))";

Install the necessary dependencies from the lock file using poetry:

poetry install


For local development / non-chromium installation you should use poetry run cb ... instead of ./ ....

Side-note, beware that poetry eats up an empty --:

# With
./ speedometer ... -- --custom-chrome-flag ...
# With poetry:
poetry run cb speedometer ... -- -- --custom-chrome-flag ...


poetry run pytest

Run detailed test coverage:

poetry run pytest --cov=crossbench --cov-report=html

Run pytype type checker:

poetry run pytype -j auto .