Carvel YTT Language Support

VS Code language support for Carvel ytt, with a focus on safe YAML coexistence and first-class support for YTT directives, annotations, and comments.

Highlights

• Dedicated ytt language mode for .ytt.yaml and .ytt.yml
• YAML injection grammar for YTT markers inside regular .yaml files
• Syntax highlighting for:
  • #@ directives like if, elif, else, for, def, load, and return
  • #@overlay/..., #@data/..., #@schema/..., and #@yaml/... annotations
  • Inline expressions like name: #@ data.values.name
  • Text templates like (@= value @)
  • #! YTT comments
• YTT-aware folding for control blocks, YAML documents, and nested YAML blocks
• Quick fix to convert plain # comments into #! comments in YTT-aware files
• Snippets for common YTT authoring patterns
• Optional ytt CLI validation command

Comment Syntax

YTT treats comment-like lines differently depending on the prefix:

• #@ executes YTT directives and annotations
• #! is the recommended YTT comment syntax
• # is plain YAML comment syntax and may be undesirable in templated files

When a file is opened as ytt, the extension uses #! for the editor line comment action.

#! this is a YTT comment
#@ load("@ytt:data", "data")

#@ if data.values.enabled:
apiVersion: v1
kind: ConfigMap
metadata:
  name: demo
data:
  owner: #@ data.values.owner
#@ else:
#! fallback branch for disabled config
data: {}
#@ end

Commands

• YTT: Preview Markers Shows the YTT directives, annotations, comments, and templates detected in the active file.
• YTT: Validate Current File Runs ytt -f <current-file> and surfaces any CLI errors as diagnostics.

Settings

• yttLanguageSupport.comments.warnOnPlainYamlComments Warn when plain # ... comments appear in YTT-aware files.
• yttLanguageSupport.validation.mode off, manual, or onSave.
• yttLanguageSupport.validation.binaryPath Path to the ytt binary used by the validation command.

Snippets

The extension contributes snippets for:

• ytt-if
• ytt-if-else
• ytt-for
• ytt-def
• ytt-load
• ytt-overlay-match
• ytt-data-values
• ytt-data-values-schema
• ytt-comment

Development

npm install
npm test

Known Notes

• The extension intentionally avoids taking over all .yaml files.
• YTT-specific folding and diagnostics only activate for ytt files or YAML files that contain YTT markers.