schemas/metadata.schema.json

{
  "$schema": "https://json-schema.org/draft/2019-09/schema",
  "type": "object",
  "required": ["platforms"],
  "additionalProperties": false,
  "properties": {
    "platforms": {
      "type": "object",
      "additionalProperties": false,
      "patternProperties": {
        "^(?![0-9])([A-Z0-9][a-z0-9]*-?)+(?<!-)$": {
          "type": "string"
        }
      }
    }
  }
}