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Post message to WebSocket connection.


To install this middleware you can use NPM:

npm install --save @middy/ws-response
npm install --save-dev @aws-sdk/client-apigatewaymanagementapi


  • AwsClient (object) (default ApiGatewayManagementApiClient): ApiGatewayManagementApi class constructor (i.e. that has been instrumented with AWS XRay). Must be from @aws-sdk/client-apigatewaymanagementapi.
  • awsClientOptions (object) (default undefined): Options to pass to ApiGatewayManagementApiClient class constructor.
  • awsClientAssumeRole (string) (default undefined): Internal key where secrets are stored. See @middy/sts on to set this.
  • awsClientCapture (function) (default undefined): Enable XRay by passing captureAWSv3Client from aws-xray-sdk in.
  • disablePrefetch (boolean) (default false): On cold start requests will trigger early if they can. Setting awsClientAssumeRole disables prefetch.


  • Lambda is required to have IAM permission for execute-api:ManageConnections
  • If awsClientOptions.endpoint is not set it will be set using event.requestContext.{domainName,stage}
  • If response does not contain ConnectId, it will be set from event.requestContext.connectionId

Sample usage

API Gateway

import middy from '@middy/core'
import wsResponse from '@middy/ws-response'

export const handler = middy((event, context) => {
return 'message'



import middy from '@middy/core'
import wsResponse from '@middy/ws-response'

const lambdaHandler = (event, context) => {
return {
ConnectionId: '...',
Data: 'message'

export const handler = middy()
awsClientOptions: {
endpoint: '...'


To exclude @aws-sdk add @aws-sdk/client-apigatewaymanagementapi to the exclude list.