Taskcluster

Interact with Mozilla Taskcluster CI. Use the native taskcluster CLI for most operations. The Python helper script (tc.py) handles only what the native CLI cannot.

Prerequisites

Taskcluster CLI

brew install taskcluster
taskcluster version

Authentication

Read-only operations (status, logs, artifacts) work without auth. Write operations require credentials.

# Sign in interactively (recommended for local use)
export TASKCLUSTER_ROOT_URL=https://firefox-ci-tc.services.mozilla.com
taskcluster signin

# Or set credentials directly
export TASKCLUSTER_CLIENT_ID=your-client-id
export TASKCLUSTER_ACCESS_TOKEN=your-access-token

Native CLI — Use for Most Operations

Always set the root URL when targeting Firefox CI:

export TASKCLUSTER_ROOT_URL=https://firefox-ci-tc.services.mozilla.com

Task Operations

# Task status
taskcluster task status <TASK_ID>

# Stream task log
taskcluster task log <TASK_ID>

# Full task definition (JSON)
taskcluster task def <TASK_ID>

# Rerun a task (same task ID)
taskcluster task rerun <TASK_ID>

# Cancel a task
taskcluster task cancel <TASK_ID>

Task Group Operations

# List all tasks in a group (with state filter options)
taskcluster group list --all <TASK_GROUP_ID>
taskcluster group list --failed <TASK_GROUP_ID>
taskcluster group list --running <TASK_GROUP_ID>

# Group status summary
taskcluster group status <TASK_GROUP_ID>

# Cancel all tasks in a group
taskcluster group cancel --force <TASK_GROUP_ID>

Worker Pool Operations

For worker pool management (list workers, terminate, bulk cancel), see references/worker-pools.md. These use taskcluster api workerManager and taskcluster api queue directly.

Python Helper — tc.py

Use this local skills checkout path:

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

The helper handles two categories the native CLI doesn't cover well:

Artifact Listing (Full JSON with URLs)

The native taskcluster task artifacts only lists names. Use tc.py when you need URLs, content types, or expiry dates to locate and download specific artifacts.

# Full artifact listing as JSON (URLs, content types, expiry)
uv run "$TC" artifacts <TASK_ID>

# For a specific run
uv run "$TC" artifacts <TASK_ID> --run 0

# Pipe to jq to find specific artifacts
uv run "$TC" artifacts <TASK_ID> | jq '.artifacts[] | select(.name | contains("log")) | .url'

Group Status with State Counts (JSON)

The native taskcluster group status output is not structured JSON. Use tc.py when you need machine-readable state counts for scripting or analysis.

# Structured JSON with totalTasks and stateCounts breakdown
uv run "$TC" group-status <TASK_GROUP_ID>

In-Tree Actions (require authentication)

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

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

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

# Retrigger via in-tree action (preserves task graph dependencies)
# Use this instead of `taskcluster task retrigger`, which clears dependencies
uv run "$TC" retrigger <TASK_ID>

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

# Confirm failures — re-runs failing tests to determine intermittent vs regression
uv run "$TC" confirm-failures <TASK_ID>

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

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

The tc.py action commands accept both task IDs and full Taskcluster URLs:

uv run "$TC" retrigger https://firefox-ci-tc.services.mozilla.com/tasks/fuCPrKG2T62-4YH1tWYa7Q

Common Workflows

Debugging Task Failures

export TASKCLUSTER_ROOT_URL=https://firefox-ci-tc.services.mozilla.com

# 1. Check task status
taskcluster task status <TASK_ID>

# 2. View logs
taskcluster task log <TASK_ID>

# 3. Inspect full definition
taskcluster task def <TASK_ID>

# 4. Check all tasks in group
taskcluster group list --all <GROUP_ID>

Retriggering Failed Tasks

# Retrigger via in-tree action (correct for Firefox CI — preserves dependencies)
uv run "$TC" retrigger <TASK_ID>

# Rerun the same task (same task ID, no new task created)
taskcluster task rerun <TASK_ID>

Note: taskcluster task retrigger clears dependencies and breaks Firefox CI tasks that depend on upstream artifacts (e.g., signing tasks needing build outputs). Always use uv run "$TC" retrigger for Firefox CI tasks.

Investigating Intermittent Failures

# 1. Check historical pass/fail rate for the test
treeherder-cli --history "test_name" --history-count 20 --repo autoland --json

# 2. Compare the failed job against similar past jobs
treeherder-cli --similar-history <JOB_ID> --similar-count 50 --repo autoland --json

# 3. Check error lines for known bug suggestions
uvx --from lumberjackth lj errors autoland <JOB_ID>

# 4. If triage suggests intermittent, confirm in CI
uv run "$TC" confirm-failures <TASK_ID>

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

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

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/
• Actions Spec: https://docs.taskcluster.net/docs/manual/using/actions/spec