A start at a render.yaml json schema

render.schema.json

{
  "$schema": "http://json-schema.org/draft-07/schema#",
  "type": "object",
  "properties": {
    "services": {
      "type": "array",
      "items": {
        "type": "object",
        "properties": {
          "type": {"type": "string"},
          "name": {"type": "string"},
          "env": {"type": "string"},
          "repo": {"type": "string"},
          "region": {"type": "string"},
          "plan": {"type": "string"},
          "branch": {"type": "string"},
          "rootDir": {"type": "string"},
          "dockerCommand": {"type": "string"},
          "numInstances": {"type": "integer"},
          "healthCheckPath": {"type": "string"},
          "envVars": {
            "type": "array",
            "items": {
              "type": "object",
              "properties": {
                "key": {"type": "string"},
                "fromService": {
                  "type": "object",
                  "properties": {
                    "type": {"type": "string"},
                    "name": {"type": "string"},
                    "property": {"type": "string"}
                  },
                  "required": ["type", "name", "property"]
                },
                "fromGroup": {"type": "string"},
                "generateValue": {"type": "boolean"},
                "sync": {"type": "boolean"},
                "value": {"type": "string"}
              },
              "required": ["key"]
            }
          },
          "disk": {
            "type": "object",
            "properties": {
              "name": {"type": "string"},
              "mountPath": {"type": "string"},
              "sizeGB": {"type": "integer"}
            },
            "required": ["name", "mountPath"]
          },
          "scaling": {
            "type": "object",
            "properties": {
              "minInstances": {"type": "integer"},
              "maxInstances": {"type": "integer"},
              "targetMemoryPercent": {"type": "integer"},
              "targetCPUPercent": {"type": "integer"}
            },
            "required": ["minInstances", "maxInstances"]
          },
          "buildCommand": {"type": "string"},
          "startCommand": {"type": "string"},
          "domains": {
            "type": "array",
            "items": {"type": "string"}
          },
          "autoDeploy": {"type": "boolean"},
          "schedule": {"type": "string"},
          "dockerfilePath": {"type": "string"},
          "dockerContext": {"type": "string"},
          "staticPublishPath": {"type": "string"},
          "pullRequestPreviewsEnabled": {"type": "boolean"},
          "buildFilter": {
            "type": "object",
            "properties": {
              "paths": {
                "type": "array",
                "items": {"type": "string"}
              },
              "ignoredPaths": {
                "type": "array",
                "items": {"type": "string"}
              }
            },
            "required": ["paths", "ignoredPaths"]
          },
          "headers": {
            "type": "array",
            "items": {
              "type": "object",
              "properties": {
                "path": {"type": "string"},
                "name": {"type": "string"},
                "value": {"type": "string"}
              },
              "required": ["path", "name", "value"]
            }
          },
          "routes": {
            "type": "array",
            "items": {
              "type": "object",
              "properties": {
                "type": {"type": "string"},
                "source": {"type": "string"},
                "destination": {"type": "string"}
              },
              "required": ["type", "source", "destination"]
            }
          },
          "ipAllowList": {
            "type": "array",
            "items": {
              "type": "object",
              "properties": {
                "source": {"type": "string"},
                "description": {"type": "string"}
              },
              "required": ["source", "description"]
            }
          },
          "maxmemoryPolicy": {"type": "string"}
        },
        "required": ["type", "name", "env"]
      }
    },
    "databases": {
      "type": "array",
      "items": {
        "type": "object",
        "properties": {
          "name": {"type": "string"},
          "databaseName": {"type": "string"},
          "user": {"type": "string"},
          "ipAllowList": {
            "type": "array",
            "items": {
              "type": "object",
              "properties": {
                "source": {"type": "string"},
                "description": {"type": "string"}
              },
              "required": ["source", "description"]
            }
          }
        },
        "required": ["name", "databaseName"]
      }
    },
    "envVarGroups": {
      "type": "array",
      "items": {
        "type": "object",
        "properties": {
          "name": {"type": "string"},
          "envVars": {
            "type": "array",
            "items": {
              "type": "object",
              "properties": {
                "key": {"type": "string"},
                "value": {"type": "string"},
                "generateValue": {"type": "boolean"},
                "sync": {"type": "boolean"}
              },
              "required": ["key"]
            }
          }
        },
        "required": ["name", "envVars"]
      }
    }
  },
  "required": ["services", "databases", "envVarGroups"]
}