In Depth Tutorial on Writing a Slackbot

(This is a repost of an article I wrote on Monsoon’s blog prior to Capital One acquiring us.)

At Monsoon (my employer), we are avid users of Slack. It’s a great collaboration tool in addition to adding a new social dimension to the office. We just crossed 500k messages sent over the platform and we’ve only been on it for a few months!

We recently held a 4-hour slackathon at Monsoon where people were tasked with writing the most useful Slack bot they could think up. The winner was a secret polling script that we use to vote on controversial topics such as what to name our teams or who the coolest person in the office is. We chose to do our event using Hubot, a popular open source bot framework written by Github. Half of the participants were mobile developers, so JavaScript, the hubot scripting language, was foreign to them. We spent a few minutes prior to the event training everybody on how to write scripts to ensure an even playing field.

I’d like to share our Slack tutorial with the rest of the community.

Setting it up takes 5 minutes

To get started with the tutorial, you’ll need to setup your machine by installing Hubot. The most important step is the first two: clone the repo and then run:

$ npm install

Once you’ve done that, you’re ready to write scripts! In the scripts folder you’ll find a file called This example script is a more feature-rich set of examples than the default that comes with Hubot. We’ll go over these examples in greater detail below.

The first thing to notice is that this is a “coffee” file. CoffeeScript is a language that compiles into JavaScript. It is popular with some communities due to its terseness compared to JavaScript. If you don’t like it, you’re welcome to write scripts in JavaScript by naming your file .js instead of .coffee.

Talking to the Bot – robot.respond

In the next step, we start working with a bot.  All bot behaviors start with a listener. The first one we’ll review listens for messages directed at the bot.

When you mention the bot directly in a room via @botname, followed by the command, the bot will execute the above block of code. In this case, it will look for the text “@botname sleep it off.” This behavior will also trigger if you privately message the bot with the text “sleep it off.”

Either of these will trigger the bot to run the command msg.send ‘zzz…’

Making the Bot Say Stuff – msg.send

Now that the bot is listening for messages directed at it, let’s see if we can get it to talk back.  The msg.send command tells the bot to send out a message to the current chat room (that told it to “sleep it off”). In this case, the bot will say, “zzz…” publicly. msg.send always replies in the same channel it detects the original message.

It Sees Everything – robot.hear

We’ve already programmed a bot to respond to messages directed at it, but you can program a bot to listen to conversation anywhere in the office, and respond to a specific word or phrase.  The second type of listener is robot.hear, a blanket listener that reacts to a phrase regardless of who it is directed at.

In this example, we are using the regular expression looking for the word (and not just a phrase containing) “up.” If anybody says “up,” this block will trigger. It will also trigger if you direct “up” at the bot; both of these would trigger the behavior:

Michi: up
Michi: @botname up

It Can Remember – robot.brain

Bots can also store information for retrieval later.  In the “up” example above, the robot initializes and/or increments a value which we save as everything_uppity_count. It does nothing more. In this case, a user can say, “up” all they want and nothing will seemingly happen while the counter increases. This is done through the “brain,” which is a simple key-value store.

Note that the “brain” uses Redis to store its contents. This way, if the bot restarts, the data is preserved. If Redis is not running, the bot will still function, but all data is lost next time the bot restarts.

In the second example of robot.hear, the bot retrieves the current value of everything_uppity_count and displays it via msg.send. As a reminder, this means the robot would just reply in the chat room that it heard the “are we up?” statement.

Calling People Out – msg.reply

Bots can add tailored prefixes to their responses. You can use the command msg.reply for this. msg.reply probably does *not* do what you think it does. Rather, it acts similarly to msg.send except that it prefixes whoever authored the original message it is replying to.

In the above example, the script will simply reply to the original sender as illustrated in the following theoretical exchange:

Michi: What’s up!
Bot: @Michi What’s up!

Note that the reply is in the channel where you sent the original message. If this was a private chat room between you and the bot, the reply would have appeared there.

Replying to Private Messages – Advanced msg.send

Handling private messages is a little more tricky. This is because Hubot doesn’t treat private messages differently from any other types of message. Instead, you have to examine the room that the message is sent in.

In order to reply to a private message, you need to check if the room shares the name with the bot. If the channel names are the same, it is implied that the channel is a private channel. We’ve provided the helper methods to accomplish this:

Starting New Private Conversations – robot.messageRoom

Sending unsolicited private messages is more straightforward. Just remember that private messages are just another room named after a user. To accomplish this, simply tell the bot to message a room:

Notice that an error can be thrown if the channel is invalid. In that case, it’s a good idea to catch the error so that the bot does not crash.

More Examples!

The example script file also includes an example of how to run a web service in the bot to listen for external data sources (such as a github webhook) and how to trigger/watch custom events. Take a look – and when you’ve finished, hopefully you’ll have as much fun designing bots and expanding your office interactions and conversations as we have had here at Monsoon!