Fuzzy Selector

The fuzzy selector uses a tool called fzf. It allows you to filter down all of the task labels from a terminal based UI and an intelligent fuzzy finding algorithm. If the fzf binary is not installed, you’ll be prompted to bootstrap it on first run.

Selecting Tasks

Running mach try fuzzy without arguments will open up the fzf interface with all of the available tasks pre-populated on the left. If you start typing, you’ll notice tasks are instantly filtered with a fuzzy match. You can select tasks by Ctrl+Click with the mouse or by using the following keyboard shortcuts:

Ctrl-K / Down  => Move cursor up
Ctrl-J / Up    => Move cursor down
Tab            => Select task + move cursor down
Shift-Tab      => Select task + move cursor up
Ctrl-A         => Select all currently filtered tasks
Ctrl-D         => De-select all currently filtered tasks
Ctrl-T         => Toggle select all currently filtered tasks
Alt-Bspace     => Clear input
?              => Toggle preview pane

Notice you can type a query, select some tasks, clear the query and repeat. As you select tasks notice they get listed on the right. This is the preview pane, it is a view of what will get scheduled when you’re done. When you are satisfied with your selection, press Enter and all the tasks in the preview pane will be pushed to try. If you changed your mind you can press Esc or Ctrl-C to exit the interface without pushing anything to try.

Unlike the syntax selector, the fuzzy selector doesn’t use the commit message to pass information up to taskcluster. Instead, it uses a file that lives at the root of the repository called try_task_config.json. You can read more information in the taskcluster docs.

Specifying Queries on the Command Line

Sometimes it’s more convenient to skip the interactive interface and specify a query on the command line with -q/--query. This is equivalent to opening the interface then typing: <query><ctrl-a><enter>.

For example:

# selects all mochitest tasks
$ mach try fuzzy --query "mochitest"

You can pass in multiple queries at once and the results of each will be joined together:

# selects all mochitest and reftest tasks
$ mach try fuzzy -q "mochitest" -q "reftest"

If instead you want the intersection of queries, you can pass in -x/--and:

# selects all windows mochitest tasks
$ mach try fuzzy --and -q "mochitest" -q "windows"

Modifying Presets

Presets make it easy to run a pre-determined set of tasks. But sometimes you might not want to run that set exactly as is, you may only want to use the preset as a starting point then add or remove tasks as needed. This can be accomplished with -q/--query or -i/--interactive.

Here are some examples of adding tasks to a preset:

# selects all perf tasks plus all mochitest-chrome tasks
$ mach try fuzzy --preset perf -q "mochitest-chrome"

# adds tasks to the perf preset interactively
$ mach try fuzzy --preset perf -i

Similarly, -x/--and can be used to filter down a preset by taking the intersection of the two sets:

# limits perf tasks to windows only
$ mach try fuzzy --preset perf -xq "windows"

# limits perf tasks interactively
$ mach try fuzzy --preset perf -xi

Shell Conflicts

Unfortunately fzf’s query language uses some characters (namely ', ! and $) that can interfere with your shell when using -q/--query. Below are some tips for how to type out a query on the command line.

The ! character is typically used for history expansion. If you don’t use this feature, the easiest way to specify queries on the command line is to disable it:

# bash
$ set +H
$ ./mach try fuzzy -q "'foo !bar"

# zsh
$ setopt no_banghist
$ ./mach try fuzzy -q "'foo !bar"

If using bash, add set +H to your ~/.bashrc, ~/.bash_profile or equivalent. If using zsh, add setopt no_banghist to your ~/.zshrc or equivalent.

If you don’t want to disable history expansion, you can escape your queries like this:

# bash
$ ./mach try fuzzy -q $'\'foo !bar'

# zsh
$ ./mach try fuzzy -q "'foo \!bar"

The third option is to use -e/--exact which reverses the behaviour of the ' character (see Additional Arguments for more details). Using this flag means you won’t need to escape the ' character as often and allows you to run your queries like this:

# bash and zsh
$ ./mach try fuzzy -eq 'foo !bar'

This method is only useful if you find you almost always prefix terms with ' (and rarely use fuzzy terms). Otherwise as soon as you want to use a fuzzy match you’ll run into the same problem as before.


All the examples in these three approaches will select the same set of tasks.

If you use fish shell, you won’t need to escape !, however you will need to escape $:

# fish
$ ./mach try fuzzy -q "'foo !bar baz\$"

Test Paths

One or more paths to a file or directory may be specified as positional arguments. When specifying paths, the list of available tasks to choose from is filtered down such that only suites that have tests in a specified path can be selected. Notably, only the first chunk of each suite/platform appears. When the tasks are scheduled, only tests that live under one of the specified paths will be run.


When using paths, be aware that all tests under the specified paths will run in the same chunk. This might produce a different ordering from what gets run on production branches, and may yield different results.

For suites that restart the browser between each manifest (like mochitest), this shouldn’t be as big of a concern.

Paths can be used with the interactive fzf window, or using the -q/--query argument. For example, running:

$ mach try fuzzy layout/reftests/reftest-sanity -q "!pgo !cov !asan 'linux64"

Would produce the following try_task_config.json:


Inside of these tasks, the reftest harness will only run tests that live under layout/reftests/reftest-sanity.

Additional Arguments

There are a few additional command line arguments you may wish to use:

-e/--exact By default, fzf treats terms as a fuzzy match and prefixing a term with ' turns it into an exact match. If passing in --exact, this behaviour is reversed. Non-prefixed terms become exact, and a ' prefix makes a term fuzzy.

--full By default, only target tasks (e.g tasks that would normally run on mozilla-central) are generated. Passing in --full allows you to select from all tasks. This is useful for things like nightly or release tasks.

-u/--update Update the bootstrapped fzf binary to the latest version.

For a full list of command line arguments, run:

$ mach try fuzzy --help

For more information on using fzf, run:

$ man fzf