AWS SAM YAML template - Unknown Tag !Ref

Solution 1:

You can add custom YAML tags in your settings.json:

"yaml.customTags": [
  "!Equals sequence",
  "!FindInMap sequence",
  "!GetAtt",
  "!GetAZs",
  "!ImportValue",
  "!Join sequence",
  "!Ref",
  "!Select sequence",
  "!Split sequence",
  "!Sub"
]

Solution 2:

First validate your extensions, I eliminated the extension called Redhat yaml and problems solved, I have the next extensions and everything is ok.

vscode-cfn-lint
Serverless IDE
aws-cloudformation-yaml
AWS Toolkit for Visual Studio Code

Solution 3:

This error message is almost certainly a false-positive from the YAML parser your IDE is using. To assess the correctness of the AWS SAM template, you should use cfn-python-lint instead, which comes with plugins for most major IDEs (unfortunately not for Visual Studio, but for Visual Studio Code).

Solution 4:

The CloudFormation Visual Studio Code extension should manage these tags for you

Solution 5:

The Ansible extension for Visual Studio Code was causing this error message for me. I removed it, and that solved the problem for my situation.