Taskcluster

Interact with Mozilla Taskcluster CI using the official taskcluster CLI.

Use this local skills checkout path for commands in this file:

SKILLS_ROOT=/Users/jwmoss/github_moz/agent-skills/skills
TC="$SKILLS_ROOT/taskcluster/scripts/tc.py"

Usage

# Query task status
uv run "$TC" status <TASK_ID>

# Get task logs
uv run "$TC" log <TASK_ID>

# List task artifacts
uv run "$TC" artifacts <TASK_ID>

# Get full task definition
uv run "$TC" definition <TASK_ID>

# Retrigger a task (uses in-tree action API for proper dependency handling)
uv run "$TC" retrigger <TASK_ID>

# Rerun a task (same task ID)
uv run "$TC" rerun <TASK_ID>

# Cancel a task
uv run "$TC" cancel <TASK_ID>

# List tasks in a group
uv run "$TC" group-list <TASK_GROUP_ID>

# Get task group status
uv run "$TC" group-status <TASK_GROUP_ID>

# Extract task ID from Taskcluster URL
uv run "$TC" status https://firefox-ci-tc.services.mozilla.com/tasks/fuCPrKG2T62-4YH1tWYa7Q

# --- In-Tree Actions (require authentication) ---

# List available actions for a task
uv run "$TC" action-list <TASK_ID>

# Confirm failures - re-run failing tests to determine if intermittent
uv run "$TC" confirm-failures <TASK_ID>

# Backfill - run test on previous pushes to find regression range
uv run "$TC" backfill <TASK_ID>

# Retrigger multiple times (default 5)
uv run "$TC" retrigger-multiple <TASK_ID> --times 10

# Trigger any action by name
uv run "$TC" action <TASK_ID> <ACTION_NAME> --input '{"key": "value"}'

Prerequisites

1. Taskcluster CLI

The skill uses the taskcluster CLI which should be installed via Homebrew:

brew install taskcluster

Check installation:

taskcluster version

2. Authentication (Optional)

Most read-only operations (status, logs, artifacts) work without authentication. For write operations (retrigger, cancel), you need Taskcluster credentials.

Option 1: Environment Variables

export TASKCLUSTER_ROOT_URL=https://firefox-ci-tc.services.mozilla.com
export TASKCLUSTER_CLIENT_ID=your-client-id
export TASKCLUSTER_ACCESS_TOKEN=your-access-token

Option 2: Configuration File

Create ~/.config/taskcluster/credentials.json or use the CLI:

taskcluster signin

Option 3: 1Password CLI

Store credentials in 1Password and configure in config.toml:

cd scripts
cp config.toml.example config.toml

Edit the config.toml to specify your 1Password item and vault.

Common Workflows

Debugging Task Failures

1. Check task status: uv run "$TC" status <TASK_ID>
2. View logs: uv run "$TC" log <TASK_ID>
3. Inspect full definition: uv run "$TC" definition <TASK_ID>
4. Check all tasks in group: uv run "$TC" group-list <GROUP_ID>

Working with Treeherder Tasks

When you have a Treeherder URL like:

https://treeherder.mozilla.org/jobs?repo=try&revision=ed901414ea5ec1e188547898b31d133731e77588

1. Use the treeherder skill to get task IDs
2. Use this skill to query individual tasks

Retriggering Failed Tasks

# Retrigger uses the in-tree action API for proper task graph handling
# This preserves dependencies and works correctly for Firefox CI tasks
uv run "$TC" retrigger <TASK_ID>

# Rerun attempts to rerun the same task (same task ID)
uv run "$TC" rerun <TASK_ID>

Note: The retrigger command uses the in-tree action API rather than the raw taskcluster task retrigger CLI command, which clears dependencies and breaks tasks that depend on upstream artifacts (like signing tasks needing build outputs).

In-Tree Actions (Confirm Failures, Backfill)

In-tree actions are defined in the Firefox taskgraph and triggered via Taskcluster hooks. These are the API equivalent of actions available in Treeherder’s “Custom Action” menu.

Required scopes: hooks:trigger-hook:project-gecko/in-tree-action-*

# List available actions for a failed task
uv run "$TC" action-list <TASK_ID>

# Confirm failures - re-runs failing tests to determine if intermittent or regression
# This is what Treeherder does when you: Select task > "..." > Custom Action > confirm-failures
uv run "$TC" confirm-failures <TASK_ID>

# Backfill - runs the test on previous pushes to find when a regression started
uv run "$TC" backfill <TASK_ID>

# Retrigger multiple times - useful for stress-testing intermittent failures
uv run "$TC" retrigger-multiple <TASK_ID> --times 10

# Trigger any action by name with custom input
uv run "$TC" action <TASK_ID> retrigger-custom --input '{"path": "test.js"}'

Common use case: Investigating image rollout failures

# 1. Find failed tasks using treeherder skill
uvx --from lumberjackth lj failures 2012615 -t autoland -p windows11-64-24h2 -n 5

# 2. Confirm if failures are intermittent or real regressions
uv run "$TC" confirm-failures <TASK_ID>

# 3. If regression, backfill to find the culprit push
uv run "$TC" backfill <TASK_ID>

URL Support

The skill automatically extracts task IDs from Taskcluster URLs:

# Both of these work identically:
uv run "$TC" status fuCPrKG2T62-4YH1tWYa7Q
uv run "$TC" status https://firefox-ci-tc.services.mozilla.com/tasks/fuCPrKG2T62-4YH1tWYa7Q

Supported URL formats:

• https://firefox-ci-tc.services.mozilla.com/tasks/<TASK_ID>
• https://stage.taskcluster.nonprod.cloudops.mozgcp.net/tasks/<TASK_ID>
• https://community-tc.services.mozilla.com/tasks/<TASK_ID>

Output Formats

All commands except log return JSON output that can be piped to jq:

# Get only failed tasks from a group
uv run "$TC" group-list <GROUP_ID> | jq '.tasks[] | select(.status.state == "failed")'

# List artifact names
uv run "$TC" artifacts <TASK_ID> | jq '.artifacts[].name'

Related Skills

• treeherder: Query CI job results by revision to get task IDs
• lando: Check landing job status
• os-integrations: Run Firefox mach try commands

References

• references/actions.md – Detailed guide to in-tree actions (confirm-failures, backfill, etc.)
• references/examples.md – Common usage patterns and workflows
• references/integration.md – Integration with other Mozilla tools
• references/worker-pools.md – Worker pool management, bulk operations, and emergency shutdown procedures

Documentation

• Taskcluster Docs: https://docs.taskcluster.net/
• Taskcluster CLI: https://github.com/taskcluster/taskcluster/tree/main/clients/client-shell
• Firefox CI: https://firefox-ci-tc.services.mozilla.com/
• Community Taskcluster: https://community-tc.services.mozilla.com/
• Actions Spec: https://docs.taskcluster.net/docs/manual/using/actions/spec