Check Your YAML Before It Checks You

By: Michael R. Bagnall

Last Updated: July 14, 2026

Every Probo build starts with your .probo.yaml file, which makes it the single most important file in your repository - and the easiest one to break. YAML is unforgiving: one tab character where a space should be, one misaligned indent, one missing space after a colon, and your builds quietly stop triggering. No error page, no failing step. Just silence, and a pull request with no environment attached.

We see it in support requests all the time, so we built something to catch it earlier.

The YAML Syntax Checker

Our new YAML syntax checking tool lives right in the documentation. Paste in the contents of your .probo.yaml file, click Check YAML, and you get an immediate answer. Syntax errors come back with the line and column, the reason, and a snippet pointing at the offending line. Valid files get a summary of your top level keys and every build step you have defined, so you can confirm the file says what you think it says before you commit it.

The whole thing runs in your browser. Nothing you paste is ever sent to us or anyone else, so it is safe to check configurations that reference private URLs or internal hostnames.

Good YAML Is Documentation

While we have your attention on the subject: treat your .probo.yaml file like the code it is. Give every step a name that says what it actually does. Keep your indentation consistent. And use comments - lines beginning with # are ignored by the parser, and they cost you nothing:

steps:
  - name: Site Setup
    plugin: Drupal
    # Trimmed copy of production - refresh it monthly.
    database: dev.sql.gz
    databaseGzipped: true

Six months from now, the teammate staring at a failing build will not remember why that database asset is named what it is or why a step exists at all. A one-line comment answers the question before it gets asked. Comment generously; your future self is the audience.

Try the checker the next time you touch your configuration, and happy building.

Related Articles & Information

---

Checking & Debugging YAML Configuring the .probo.yaml File Builds Don't Trigger