JSON Schema based on https://concourse-ci.org/tasks.html#schema.task.

.vscode∕extensions.json

{
    "recommendations": [
        "redhat.vscode-yaml"
    ]
}

.vscode∕settings.json

{
    "files.eol": "\n"
    , "json.schemas": [
        {
          "fileMatch": ["*.yaml"],
          "url": "./.jsonschema/concourse.task.schema.json"
        }
      ]
    , "yaml.schemas": {
      "./.jsonschema/concourse.task.schema.json": [
        "*.yaml"
      ]
    }
}

concourse.task.schema.json

{
    "$id": "https://concourse-ci.org/concouse.task.schema.json",
    "$schema": "http://json-schema.org/draft-07/schema#",
    "title": "Task",
    "description": "Schema based on https://concourse-ci.org/tasks.html#schema.task",
    "type": "object",
    "properties": {
        "platform": {
            "description": "The platform the task should run on. This determines the pool of workers that the task can run against.",
            "$ref": "#/definitions/platform_type"
        },
        "image_resource": {
            "description": "The container image to run with, as provided by an anonymous resource definition",
            "$ref": "#/definitions/anonymous_resource"
        },
        "inputs": {
            "type":"array",
            "items": {
                "$ref": "#definitions/input"
            }
        },
        "outputs": {
            "type":"array",
            "items": {
                "$ref": "#definitions/output"
            }
        },
        "caches": {
            "type":"array",
            "items": {
                "$ref": "#definitions/cache"
            }
        },
        "params": {
            "$ref": "#definitions/env-vars"
        },
        "run": {
            "$ref": "#definitions/command"
        },
        "rootfs_uri": {
            "type": "string"
        },
        "container_limits": {
            "$ref": "#definitions/container_limits"
        }
    },
    "additionalProperties": false,
    "required": ["platform", "image_resource", "run"],
    "definitions": {
        "platform_type": {
            "type": "string",
            "enum": ["linux", "darwin", "windows"]
        },
        "anonymous_resource": {
            "type": "object",
            "properties" : {
                "type": {
                    "$ref": "#definitions/resource_type_name"
                },
                "source": {
                    "$ref": "#definitions/config"
                },
                "params": {
                    "$ref": "#definitions/config"
                },
                "version": {
                    "$ref": "#definitions/version"
                }
            },
            "additionalProperties": false,
            "required": ["type", "source"]
        },
        "resource_type_name": {
            "type": "string",
            "enum": ["registry-image", "docker-image","git"]
        },
        "config": {
            "type": "object",
            "propertyNames": {
                "pattern": "^[A-Za-z_][A-Za-z0-9_]*$"
            }
        },
        "version": {
            "type": "object",
            "additionalProperties": { "type": "string" }
        },
        "input": {
            "type": "object",
            "properties": {
                "name":{"$ref": "#definitions/identifier"},
                "path":{"$ref": "#definitions/dir-path"},
                "optional":{"type": "boolean"}
            },
            "additionalProperties": false,
            "required": ["name"]
        },
        "output": {
            "type": "object",
            "properties": {
                "name":{"$ref": "#definitions/identifier"},
                "path":{"$ref": "#definitions/dir-path"}
            },
            "additionalProperties": false,
            "required": ["name"]
        },
        "cache": {
            "type": "object",
            "properties": {
                "path":{"$ref": "#definitions/dir-path"}
            },
            "additionalProperties": false,
            "required": ["path"]
        },
        "env-vars": {
            "type": "object",
            "additionalProperties": { "type": "string" }
        },
        "command": {
            "type": "object",
            "properties": {
                "path":{"$ref": "#definitions/file-path"},
                "args":{"type": "array", "items":{"type": "string"}},
                "dir": {"$ref": "#definitions/dir-path"},
                "user": {"type": "string"}
            },
            "additionalProperties": false,
            "required": ["path"]
        },
        "identifier": {
            "type": "string",
            "pattern": "^[a-z].*$"
        },
        "dir-path": {"type": "string"},
        "file-path": {"type": "string"},
        "container_limits": {
            "type": "object",
            "properties": {
                "cpu":{"type":"number", "minimum": 0},
                "memory":{"type":"number", "minimum": 0}
            },
            "additionalProperties": false
        }
    }
}