pre-commit "check-yaml...Failed" in CI

By Daniel Zoghalchali·Latchkey

The pre-commit check-yaml hook loads every staged YAML file. When one does not parse, the hook prints "Failed" with the parser error and the file, and the run exits non-zero.

What this error means

pre-commit output shows "check-yaml...............Failed" followed by the YAML parse error and the offending filename.

check-yaml...............................................................Failed
- hook id: check-yaml
- exit code: 1

config.yaml: could not determine a constructor for the tag '!Ref'
mapping values are not allowed here
  in "config.yaml", line 6, column 12

Common causes

A genuine YAML syntax error

A tab, bad indentation, an unquoted colon, or a duplicate key stops the parser, exactly as it would in any consumer.

Custom tags the loader rejects

CloudFormation !Ref/!GetAtt or other custom tags fail the default safe loader unless --unsafe is set to allow syntax-only checking.

How to fix it

Fix the reported YAML

1. Open the file at the line:column in the hook output.
2. Correct the syntax (quote colons, remove tabs, dedupe keys).
3. Re-run pre-commit run check-yaml --all-files.

pre-commit run check-yaml --all-files

Allow custom tags with --unsafe

For CloudFormation and similar custom tags, pass --unsafe so check-yaml validates syntax without resolving the tags.

- repo: https://github.com/pre-commit/pre-commit-hooks
  rev: v4.6.0
  hooks:
    - id: check-yaml
      args: [--unsafe]

How to prevent it

• Run pre-commit locally so YAML errors never reach CI.
• Use --unsafe only for files with legitimate custom tags.
• Pair check-yaml with yamllint for style plus syntax.

Frequently asked questions

Related guides

References

• GitHub Actions documentation