This document shows how to define an action in-tree such that it shows up in supported user interfaces like Treeherder. For details on interface between in-tree logic and external user interfaces, see the actions.json spec.

At a very high level, the process looks like this:

  • The decision task produces an artifact, public/actions.json, indicating what actions are available.

  • A user interface (for example, Treeherder or the Taskcluster tools) consults actions.json and presents appropriate choices to the user, if necessary gathering additional data from the user, such as the number of times to re-trigger a test case.

  • The user interface follows the action description to carry out the action. In most cases (action.kind == 'task'), that entails creating an “action task”, including the provided information. That action task is responsible for carrying out the named action, and may create new sub-tasks if necessary (for example, to re-trigger a task).

Defining Action Tasks

There is one options for defining actions: creating a callback action. A callback action automatically defines an action task that will invoke a Python function of your devising.

Creating a Callback Action


You can generate actions.json on the command line with ./mach taskgraph actions.

A callback action is an action that calls back into in-tree logic. That is, you register the action with name, title, description, context, input schema and a python callback. When the action is triggered in a user interface, input matching the schema is collected, passed to a new task which then calls your python callback, enabling it to do pretty much anything it wants to.

To create a new callback action you must create a file taskcluster/gecko_taskgraph/actions/, that at minimum contains:

from __future__ import absolute_import, print_function, unicode_literals

from .registry import register_callback_action

    title='Say Hello',
    symbol='hw',  # Show the callback task in treeherder as 'hw'
    description="Simple **proof-of-concept** callback action",
    order=10000,  # Order in which it should appear relative to other actions
def hello_world_action(parameters, graph_config, input, task_group_id, task_id, task):
    print("Hello was triggered from taskGroupId: {}".format(task_group_id))

The arguments are:


an instance of taskgraph.parameters.Parameters, carrying decision task parameters from the original decision task.


an instance of taskgraph.config.GraphConfig, carrying configuration for this tree


the input from the user triggering the action (if any)


the target task group on which this action should operate


the target task on which this action should operate (or None if it is operating on the whole group)


the definition of the target task (or None, as for task_id)

The example above defines an action that is available in the context-menu for the entire task-group (result-set or push in Treeherder terminology). To create an action that shows up in the context menu for a task we would specify the context parameter.

The order value is the sort key defining the order of actions in the resulting actions.json file. If multiple actions have the same name and match the same task, the action with the smallest order will be used.

Setting the Action Context

The context parameter should be a list of tag-sets, such as context=[{"platform": "linux"}], which will make the task show up in the context-menu for any task with task.tags.platform = 'linux'. Below is some examples of context parameters and the resulting conditions on task.tags (tags used below are just illustrative).

context=[{"platform": "linux"}]:

Requires task.tags.platform = 'linux'.

context=[{"kind": "test", "platform": "linux"}]:

Requires task.tags.platform = 'linux' and task.tags.kind = 'test'.

context=[{"kind": "test"}, {"platform": "linux"}]:

Requires task.tags.platform = 'linux' or task.tags.kind = 'test'.


Requires nothing and the action will show up in the context menu for all tasks.


Is the same as not setting the context parameter, which will make the action show up in the context menu for the task-group. (i.e., the action is not specific to some task)

The example action below will be shown in the context-menu for tasks with task.tags.platform = 'linux':

from registry import register_callback_action

    symbol='re-c',  # Show the callback task in treeherder as 're-c'
    description="Create a clone of the task",
    context=[{'platform': 'linux'}]
def retrigger_action(parameters, graph_config, input, task_group_id, task_id, task):
    # input will be None
    print "Retriggering: {}".format(task_id)
    print "task definition: {}".format(task)

When the context parameter is set, the task_id and task parameters will provided to the callback. In this case the task_id and task parameters will be the taskId and task definition of the task from whose context-menu the action was triggered.

Typically, the context parameter is used for actions that operate on tasks, such as retriggering, running a specific test case, creating a loaner, bisection, etc. You can think of the context as a place the action should appear, but it’s also very much a form of input the action can use.

Specifying an Input Schema

In call examples so far the input parameter for the callbacks has been None. To make an action that takes input you must specify an input schema. This is done by passing a JSON schema as the schema parameter.

When designing a schema for the input it is important to exploit as many of the JSON schema validation features as reasonably possible. Furthermore, it is strongly encouraged that the title and description properties in JSON schemas is used to provide a detailed explanation of what the input value will do. Authors can reasonably expect JSON schema description properties to be rendered as markdown before being presented.

The example below illustrates how to specify an input schema. Notice that while this example doesn’t specify a context it is perfectly legal to specify both input and context:

from registry import register_callback_action

    title='Run All Tasks',
    symbol='ra-c',  # Show the callback task in treeherder as 'ra-c'
    description="**Run all tasks** that have been _optimized_ away.",
        'title': 'Action Options',
        'description': 'Options for how you wish to run all tasks',
        'properties': {
            'priority': {
                'title': 'priority'
                'description': 'Priority that should be given to the tasks',
                'type': 'string',
                'enum': ['low', 'normal', 'high'],
                'default': 'low',
            'runTalos': {
                'title': 'Run Talos'
                'description': 'Do you wish to also include talos tasks?',
                'type': 'boolean',
                'default': 'false',
        'required': ['priority', 'runTalos'],
        'additionalProperties': False,
def retrigger_action(parameters, graph_config, input, task_group_id, task_id, task):
    print "Create all pruned tasks with priority: {}".format(input['priority'])
    if input['runTalos']:
        print "Also running talos jobs..."

When the schema parameter is given the callback will always be called with an input parameter that satisfies the previously given JSON schema. It is encouraged to set additionalProperties: false, as well as specifying all properties as required in the JSON schema. Furthermore, it’s good practice to provide default values for properties, as user interface generators will often take advantage of such properties.

It is possible to specify the schema parameter as a callable that returns the JSON schema. It will be called with a keyword parameter graph_config with the graph configuration <taskgraph-graph-config> of the current taskgraph.

Once you have specified input and context as applicable for your action you can do pretty much anything you want from within your callback. Whether you want to create one or more tasks or run a specific piece of code like a test.

Conditional Availability

The decision parameters taskgraph.parameters.Parameters passed to the callback are also available when the decision task generates the list of actions to be displayed in the user interface. When registering an action callback the availability option can be used to specify a callable which, given the decision parameters, determines if the action should be available. The feature is illustrated below:

from registry import register_callback_action

    title='Say Hello',
    symbol='hw',  # Show the callback task in treeherder as 'hw'
    description="Simple **proof-of-concept** callback action",
    # Define an action that is only included if this is a push to try
    available=lambda parameters: parameters.get('project', None) == 'try',
def try_only_action(parameters, graph_config, input, task_group_id, task_id, task):
    print "My try-only action"

Properties of parameters are documented in the parameters section. You can also examine the parameters.yml artifact created by decisions tasks.

Context can be similarly conditionalized by passing a function which returns the appropriate context:

context=lambda params:
    [{}] if int(params['level']) < 3 else [{'worker-implementation': 'docker-worker'}],

Creating Tasks

The create_tasks utility function provides a full-featured way to create new tasks. Its features include creating prerequisite tasks, operating in a “testing” mode with ./mach taskgraph test-action-callback, and generating artifacts that can be used by later action tasks to figure out what happened. See the source for more detailed docmentation.

The artifacts are:

task-graph.json (or task-graph-<suffix>.json:

The graph of all tasks created by the action task. Includes tasks created to satisfy requirements.

to-run.json (or to-run-<suffix>.json:

The set of tasks that the action task requested to build. This does not include the requirements.

label-to-taskid.json (or label-to-taskid-<suffix>.json:

This is the mapping from label to taskid for all tasks involved in the task-graph. This includes dependencies.

More Information

For further details on actions in general, see the actions.json spec. The hooks used for in-tree actions are set up by ci-admin based on configuration in ci-configuration.