Failures, on_end and limits

When a script fails

Any error in a script fails the build. That includes an uncaught exception, a syntax error, a missing import, a non-zero exit code, a crash, and running too long. Output on stderr with exit code 0 counts as success.

Where the failure shows

1. Your script's full output in the build log under build action <hook>, including the whole Python traceback or Node stack trace.
2. The build action <hook> step marked failed on the build page.
3. A summary at the end of the log that repeats the last lines of your script's error output:

=== BUILD ACTION FAILED: pre_build (.dsl/build_actions/pre_build.py) ===
reason:   exited with code 1
runtime:  python 3.14.7                 cwd: <project folder>
duration: 4.2 s
last lines of stderr:
  Traceback (most recent call last):
    File ".../.dsl/build_actions/pre_build.py", line 12, in <module>
  FileNotFoundError: [Errno 2] No such file or directory: 'Assets/Gen/config.json'

Reading the build log and its steps is covered in Your first build.

Fail a build on purpose

Exit non-zero: sys.exit(1) in Python or process.exit(1) in Node. Use it for checks that should stop a build, such as a missing asset or a version that does not match.

Platform faults

Reporting results with on_end

on_end always runs last and is told how the build went:

This on_end.py posts the result to a chat webhook whose URL is stored as the secret CHAT_WEBHOOK_URL (see Secrets in build actions):

# .dsl/build_actions/on_end.py - post the result to a chat webhook
import json, os, urllib.request

secrets = json.load(open(os.environ["DSL_SECRETS_FILE"]))
result = os.environ["DSL_BUILD_RESULT"]
text = f'{os.environ["DSL_PROJECT"]} {os.environ["DSL_VERSION"]}.{os.environ["DSL_BUILD_NUMBER"]} ({os.environ["DSL_CONFIGURATION"]}): {result}'
if result != "success":
    text += f' - {os.environ.get("DSL_FAILED_PHASE", "")}: {os.environ.get("DSL_FAILURE_MESSAGE", "")}'

req = urllib.request.Request(secrets["CHAT_WEBHOOK_URL"], data=json.dumps({"text": text}).encode(),
                             headers={"Content-Type": "application/json"})
urllib.request.urlopen(req, timeout=30)

on_end does not run when a build is canceled or interrupted by maintenance.

Limits

A script stopped by a limit fails the build, and the log names the limit it hit. For long work, split it across hooks or print progress as you go.