This is a reprint of the README from my project simple-slack-slash-supplier.

This examples project showcases a simple way to create new slash commands without having to work too hard.

This example assumes you have access to AWS Lambda as well as have created a Slash command in Slack.

Handling application/x-www-form-urlencoded

Slack sends their POST requests using Content-Type: application/x-www-form-urlencoded. This is not a content type that Lambda supports out-of-the-box. We need to do some legwork in order to map that raw request body to JSON which we can understand more easily in our Node.js handler function.

Preliminary setup:

  • You must create a standalone POST resource action
  • Be sure “Integration type” is set to “Lambda Function”
  • Make sure Use Lambda Proxy integration is checked
  • Remove the original ANY resource action to be sure it doesn’t conflict

Mapping templates

In order to properly handle application/x-www-form-urlencoded, we need to make a mapping template for it.

Here are the steps:

  • Click on “Integration Request” when viewing the details of your POST resource action
  • Pop open the “Mapping templates” accordion
  • Click “Add mapping template”
  • Use application/x-www-form-urlencoded in the field that appears
  • Scroll down and see the new form to enter in your template details
  • Select “Method request passthrough” from the “Generate template” dropdown
  • Put the following content in the textarea:
##  Ripped from ""
    "body-json" : $input.json('$'),
    "params" : {
        #foreach( $token in $input.path('$').split('&') )
            #set( $keyVal = $token.split('=') )
            #set( $keyValSize = $keyVal.size() )
            #if( $keyValSize >= 1 )
                #set( $key = $util.urlDecode($keyVal[0]) )
                #if( $keyValSize >= 2 )
                    #set( $val = $util.urlDecode($keyVal[1]) )
                    #set( $val = '' )
                "$key": "$util.escapeJavaScript($val)"#if($foreach.hasNext),#end
    "stage-variables" : {
        #foreach($key in $stageVariables.keySet())
        "$key" : "$util.escapeJavaScript($stageVariables.get($key))"
    "context" : {
        "account-id" : "$context.identity.accountId",
        "api-id" : "$context.apiId",
        "api-key" : "$context.identity.apiKey",
        "authorizer-principal-id" : "$context.authorizer.principalId",
        "caller" : "$context.identity.caller",
        "cognito-authentication-provider" : "$context.identity.cognitoAuthenticationProvider",
        "cognito-authentication-type" : "$context.identity.cognitoAuthenticationType",
        "cognito-identity-id" : "$context.identity.cognitoIdentityId",
        "cognito-identity-pool-id" : "$context.identity.cognitoIdentityPoolId",
        "http-method" : "$context.httpMethod",
        "stage" : "$context.stage",
        "source-ip" : "$context.identity.sourceIp",
        "user" : "$context.identity.user",
        "user-agent" : "$context.identity.userAgent",
        "user-arn" : "$context.identity.userArn",
        "request-id" : "$context.requestId",
        "resource-id" : "$context.resourceId",
        "resource-path" : "$context.resourcePath"
  • Paste the content above in the textarea
  • Click “Save” to confirm the content of the textarea
  • From the “Actions” dropdown select “Deploy API”
  • Deploy the API changes as you normally would

Now you should now be able to handle POST requests with content type of application/x-www-form-urlencoded and they will be converted right into JSON automatically!


You can edit hello-command.json to add details about your command in order to test the different handlers. Add new files and new tests scripts to package.json to keep going.

Run the commands with:

npm install
npm run test