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Custom Data for CSS Language Service

In VS Code, there are two ways of loading custom CSS datasets:

  1. With setting css.experimental.customData
  2. With an extension that contributes contributes.css.experimental.customData

Both setting point to a list of JSON files. This document describes the shape of the JSON files.

Custom Data Format

🚧 The data format is in experimental phase and subject to change. 🚧


The JSON have one required property, version, and 4 other top level properties:

  "version": 1,
  "properties": [],
  "atDirectives": [],
  "pseudoClasses": [],
  "pseudoElements": []

Version denotes the schema version you are using. The latest schema version is V1.

You can find other properties' shapes at cssLanguageTypes.ts or the JSON Schema.

You might want to use the json.schemas setting to check your data against the schema and get auto-completion:

  "json.schemas": [
      "fileMatch": ["/css.json"],
      "url": ""


All top-level properties share two basic properties, name and description. For example:

  "properties": [
    { "name": "foo", "description": "Foo property" }
  "atDirectives": [
    { "name": "@foo", "description": "Foo at directive" }
  "pseudoClasses": [
    { "name": ":foo", "description": "Foo pseudo class" }
  "pseudoElements": [
    { "name": ":foo", "description": "Foo pseudo elements" }

You can also specify 2 additional properties for them:

  "properties": [
      "name": "foo",
      "description": "Foo property",
      "browsers": [
      "status": "standard"
  • browsers: A list of supported browsers. The format is browserName + version. For example: ['E10', 'C30', 'FF20']. Here are all browser names:

    export let browserNames = {
      E: 'Edge',
      FF: 'Firefox',
      S: 'Safari',
      C: 'Chrome',
      IE: 'IE',
      O: 'Opera'

    The browser compatibility will be rendered at completion and hover. Items that is supported in only one browser are dropped from completion.

  • status: The status of the item. The format is:

    export type EntryStatus = 'standard' | 'experimental' | 'nonstandard' | 'obsolete';

    The status will be rendered at the top of completion and hover. For example, nonstandard items are prefixed with the message 🚨️ Property is nonstandard. Avoid using it..