YAML001 — invalid-yaml

Severity: blocker · Category: YAML · Platforms: GitHub Actions, Azure Pipelines

What it checks

Flags a pipeline file that isn't valid YAML at all — a stray tab used for indentation (YAML disallows tabs in indentation entirely), an unclosed {/[, mismatched quotes, or anything else the parser itself rejects.

Why it matters

Before this rule existed, a file that failed to parse printed an error to stderr and was silently skipped from the rest of the scan — vlotpipe check still exited 0 and reported "All checks passed!", exactly backwards for a CI gate whose entire job is to catch broken pipeline files. This is the one rule in the whole tool that can't be argued with: if the YAML doesn't parse, the platform running it won't be able to either.

Examples

Flagged — a tab character where YAML requires spaces:

jobs:
  build:
    runs-on: ubuntu-latest
    steps:
      - run: echo hi
      extra: this line is indented with a tab

Flagged — an unclosed flow mapping:

steps:
  - run: echo hi
    with: {foo: unclosed

Fixed: whatever the parser's specific complaint is, addressed — there's no generic template for "valid YAML," only the specific syntax error reported in the message.

Suppressing

No inline # vlotpipe: ignore comment — there's no parsed tree to attach one to when parsing itself is what failed. .vlotpipe.yml still works, though it's rarely the right tool here: a file that doesn't parse isn't a policy disagreement to file an exception for, it's broken.

ignore:
  - code: YAML001
    path: "vendor/generated-pipeline.yml"
    reason: "generated file with a known, tolerated templating artifact; upstream issue filed"