Extended YAML Support adds embedded-language highlighting and optional visual boundaries to tagged YAML block scalars in Visual Studio Code.

Use an explicit tag such as !python or !md before a literal (|) or folded (>) block. The block keeps normal YAML structure while its contents are highlighted as the selected language.

Features

Embedded syntax highlighting for Markdown, Python, JSON, TypeScript, Rust, shell scripts, Ruby, diffs, and TOML
Literal and folded YAML block scalars, including indentation and chomping indicators
Configurable background decorations for embedded blocks
XML-style tag highlighting and content boundaries inside embedded Markdown
No telemetry, network requests, external commands, or file writes
Supports untrusted and virtual workspaces

Examples

prompt: !md |
  # Review instructions

  <system-reminder priority="high">
  Check every assumption before editing.
  </system-reminder>

script: !python |-
  from pathlib import Path

  print(Path.cwd())

config: !json >
  {"enabled": true, "retries": 3}

implementation: !typescript |
  const enabled: boolean = true;

query: !shell |
  printf '%s\n' "ready"

Supported tags

Embedded language	Tags
Markdown	`!md`, `!markdown`
Python	`!py`, `!python`
JSON	`!json`
TypeScript	`!ts`, `!typescript`
Rust	`!rs`, `!rust`
Shell	`!bash`, `!sh`, `!shell`
Ruby	`!rb`, `!ruby`
Diff	`!diff`, `!patch`
TOML	`!toml`

Tags are case-sensitive. The tag must be attached to a YAML block scalar.

Installation

Install Extended YAML Support from the Visual Studio Code Extensions view, or run:

code --install-extension CenterForAgenticAI.extended-yaml-support

Settings

Setting	Default	Purpose
`extendedYaml.decorations.enabled`	`true`	Enables editor decorations without affecting syntax highlighting.
`extendedYaml.decorations.codeBlockBackground`	`rgba(0, 0, 0, 0.15)`	Background for embedded code.
`extendedYaml.decorations.markdownBlockBackground`	`rgba(30, 60, 90, 0.15)`	Background for embedded Markdown.
`extendedYaml.decorations.xmlTagColor`	`#e06c75`	Foreground for XML-style tags in Markdown blocks.
`extendedYaml.decorations.xmlContentBackground`	`rgba(224, 108, 117, 0.08)`	Background for paired XML-style tag contents.
`extendedYaml.decorations.debounceMilliseconds`	`75`	Delay before decorations are refreshed after an edit.

Set extendedYaml.decorations.enabled to false if you want embedded syntax highlighting without backgrounds.

YAML validation

This extension adds editor presentation only; it does not replace a YAML parser or validator. If your YAML validation extension reports the custom tags as unknown, configure that validator to recognize the tags as scalar tags.

For the Red Hat YAML extension, the equivalent setting begins like this:

{
  "yaml.customTags": [
    "!md scalar",
    "!markdown scalar",
    "!py scalar",
    "!python scalar",
    "!json scalar",
    "!ts scalar",
    "!typescript scalar"
  ]
}

Add the remaining tags you use from the table above.