Buildkite Preflight

Buildkite Preflight

Preflight runs CI builds against changes in the local working tree. It's intended to provide a feedback loop for evaluating local changes in CI by providing a single command to run the entire commit/push/run loop.

When to Run Preflight

• After completing the requested implementation and local tests pass, use preflight to run the whole test suite on CI
• Before a long unsupervised session ends if you've made multiple changes
• After fixing a failure from a previous preflight run
• Not for trivial changes like typos, comment-only edits, or single-line config tweaks unless the user asks
• When the user asks to verify changes work in CI

Before Running

• Prefer an explicit pipeline in {org}/{pipeline} form
• Ensure bk auth is pointed at the right Buildkite organization when the pipeline slug relies on local config
• Requires a git repository with at least one commit and push access to origin
• Requires read_builds, write_builds, and read_pipelines scopes; and read_suites for Test Engine results.
• Run preflight in a subagent

Running Preflight

# Human-readable output that works well in agent shells
bk preflight --pipeline my-org/my-pipeline --watch --text

# Start a run and return as soon as the build enters the failing state
bk preflight --pipeline my-org/my-pipeline --watch

# Wait for a terminal build state instead of fast-failing
bk preflight --pipeline my-org/my-pipeline --watch --exit-on=build-terminal

# Start the build and exit immediately
bk preflight --pipeline my-org/my-pipeline --no-watch

# Leave the remote preflight branch and build running on early exit
bk preflight --pipeline my-org/my-pipeline --watch --no-cleanup

# Wait for 30s after build completion for Test Engine summaries
bk preflight --pipeline my-org/my-pipeline --watch --await-test-results 30s

Do not set a timeout on a watched preflight run.

How It Works

Preflight executes the following workflow:

1. Snapshot - Captures staged, unstaged, and untracked files using a temporary git index, without modifying the real index or working tree.
2. Commit - Creates a distinct preflight commit on top of HEAD, even when the tree is clean, so the run has its own commit status context.
3. Push - Pushes that commit to refs/heads/bk/preflight/<uuid> on origin.
4. Create Build - Calls the Buildkite Create Build API and sets PREFLIGHT=true, PREFLIGHT_SOURCE_COMMIT, and PREFLIGHT_SOURCE_BRANCH when available.
5. Monitor - Watches the build and emits operation events, build status updates, job failures, retry-passed jobs, and a final summary.
6. Cleanup - Deletes the remote preflight branch when the run finishes unless --no-cleanup is set. With the default --exit-on=build-failing, early exit also cancels the remote build unless --no-cleanup is set.

The working tree is never disrupted, so you can keep editing while the build runs.

Reading the Result

• The default exit policy is build-failing, so the preflight command exits as soon as the build enters the failing state.
• --exit-on=build-terminal waits for a terminal build state (passed, failed, canceled).
• --await-test-results waits after build completion for Test Engine rollups when test runs exist.
• Final job summaries cover hard-failed script jobs and exclude non-script, broken, and soft-failed jobs
• Failed job output includes the job id. Use bk job log -b <build-number> -p <org>/<pipeline> <job-id> to inspect logs.
• When analytics are available, the final summary shows per-suite passed/failed/skipped counts and up to 10 failed tests.
• Test failures include the test name and location; reproduce the failure locally and fix it.
• If a failure is flaky/unrelated to your changes, note it to the user rather than trying to fix it.

Extracting results from the JSON build_summary event:

Just the failed jobs from the summary:

bk preflight --pipeline my-org/my-pipeline --watch --json \
  | jq -nrc --unbuffered 'inputs | select(.type == "build_summary") | .failed_jobs'

Just the failed tests from the summary:

bk preflight --pipeline my-org/my-pipeline --watch --json \
  | jq -nrc --unbuffered 'inputs | select(.type == "build_summary") | .tests.failures'

Output Modes

• Use --text for plain text logs that are easy to read in tool output
• Use --json when you need structured event data
• If neither flag is set, bk uses the interactive TTY UI when stdout is a terminal and plain text otherwise

Running a Preflight Build

Basic usage

# Run preflight and watch until completion
bk preflight --pipeline my-org/my-pipeline --watch

# Run without watching (starts the build and exits)
bk preflight --pipeline my-org/my-pipeline --no-watch

# Skip confirmation prompts (useful in scripts)
bk preflight --pipeline my-org/my-pipeline --watch --yes

# Keep the remote preflight branch after the build finishes
bk preflight --pipeline my-org/my-pipeline --watch --no-cleanup

# Use plain text output in non-interactive environments
bk preflight --pipeline my-org/my-pipeline --watch --text

# Use JSONL output when another tool needs structured events
bk preflight --pipeline my-org/my-pipeline --watch --json

# Wait for 10s for Test Engine results after build completion
bk preflight --pipeline my-org/my-pipeline --watch --await-test-results 10s

Do not set a timeout on the bash tool running preflight.

Pipeline resolution

The --pipeline flag accepts either a pipeline slug or {org slug}/{pipeline slug}:

# With org prefix (explicit)
bk preflight --pipeline my-org/my-pipeline --watch

# Pipeline slug only (org resolved from bk config)
bk preflight --pipeline my-pipeline --watch

Flags

Exit Codes

Check the exit code to determine the build result:

Further Reading

• Buildkite CLI overview
• CLI command reference
• CLI installation

Optional Workflow: Act On A Failure And Check Back Later

Begin fixing the first failure as soon as preflight exits with an incomplete build result because the build is failing. Check the same build's summary while it continues, then query failed jobs directly for subsequent failures. This allows you to quickly iterate on the first failure, and gather further failures in parallel. Use the bk preflight --no-cleanup option to ensure that build is not canceled on fast failure.

bk preflight --pipeline my-org/my-pipeline --watch --no-cleanup --text

bk preflight will return as soon as the build transitions to failing, using the default --exit-on=build-failing behavior. Setting the --no-cleanup flag is required if you want the build to continue running to completion.

Workflow:

1. Wait for preflight to exit on build failing (the default --exit-on condition).
2. Inspect the failed build's jobs logs and test failures and start fixing the issue immediately.
3. Keep the build number or preflight UUID from the run output.
4. Check the build state without downloading jobs, artifacts, annotations, or expanded pipeline details. Query failed jobs separately through the REST List Jobs endpoint:

bk build view 429 -p my-org/my-pipeline --summary --text
bk job list --pipeline my-org/my-pipeline --build 429 --state failed --no-limit --text

5. After the build reaches a terminal state and you no longer need the remote preflight branch, clean it up explicitly:

bk preflight cleanup --pipeline my-org/my-pipeline --preflight-uuid <uuid> --yes --text

bk preflight cleanup only deletes completed preflight branches, so run it after the build has finished.