Did you know that you could host a Discord bot in Vercel for free? I didn’t knew until I googled around. If you’re curious on how you could host your own bot in Vercel, follow along

The theory

I had made bots before, but they were like servers that are always on, so that the bot has an online status. But that was a long time ago. Discord supports webhooks for their slash commands, so when a user sends a command to your Discord bot, Discord will send a POST request. Vercel supports serverless functions, so it is perfect for this use case (despite them not recommending it).

Setting up your bot

You can create an application in Discord through their developer portal here. After creating your application, you will get an application ID and public key. The application ID will be used for registering/updating/deleting your commands, while the public key is for verifying if incoming requests come from Discord or not.

After that, head to the bot section and generate a token. Save it somewhere safe, because it is also used to register your slash commands.

Registering your slash command(s)

Registering your slash command can be done by sending a POST request to https://discord.com/api/v${versionNumber}/applications/${applicationId}/commands.

A sample python script is provided by Discord here, but you probably could just use Postman or even cURL. Just make sure to use Bot ${yourBotToken} for the Authorization header & follow their sample request body, the important sections are:

name: the name of your slash command (please make sure it is all lowercase, I had problems related to this before)
type: application command type, read this documentation for more info, but usually we would use 1
description: description of your slash command:
options: array of parameters, which consist of:
- name: name of your param
- description: description of your param
- type: param type, read this documentation for more info
- required: boolean, true if required, false if not, please make sure required params are first

Here is an example of my slash command:

get-random is the root name
the description is your root description

And here is an example of the option:

min-level/max-level/song-count is the name of the option
description of selected param is the description
Discord will validate the type, so if the user tries to enter text on an integer option, Discord will not send it

Creating the serverless bot

Vercel’s project structure looks like this:

api
└─index.js/ts

And their serverless function is pretty straightforward, something like this:

export default async function main(request, response) {
    // your code here
}

You will need to put a few things on the bot as the foundation:

Verify if incoming requests are from Discord or not

In order to validate if a request comes from Discord or not, the documentation here requires you to:

Make sure that X-Signature-Ed25519 exists on the request header
Make sure that X-Signature-Timestamp exists on the request header
Validate both values & the request body & your public key

Discord provides an example using tweetnacl, but I prefer discord-interactions (this npm package) because it has type definitions to help make my code tidier.

The validation would look something like this:

const signature = req.get('X-Signature-Ed25519');
const timestamp = req.get('X-Signature-Timestamp');
const isValidRequest = await verifyKey(req.rawBody, signature, timestamp, 'MY_CLIENT_PUBLIC_KEY');
if (!isValidRequest) {
    return res.status(401).end('Bad request signature');
}

Respond to pings

According to this documentation, the way Discord verifies if your endpoint works or not is by sending a PING request, so you have to respond with a PONG. It should look something like this:

if (message.type === InteractionType.PING) {
    const pingResponse: InteractionResponse = {
        type: InteractionResponseType.PONG,
    };
    response.send(pingResponse); // Basically send a {"type": 1}
}

Once you have both pieces of code in your function, you are ready to develop

Respond to slash commands

The full request send by Discord can be seen in this documentation. I will provide an example below:

if (message.type === InteractionType.APPLICATION_COMMAND) {
    switch (message.data.name.toLowerCase()) {
        case "get-song": // change with your command name
            const title = message.data.options[0].value; // access params
            const songs = await fetch(`some-api-url?title=${title}`);

            response.status(200).send({
              type: 4, // see https://discord.com/developers/docs/interactions/receiving-and-responding#interaction-response-object-interaction-callback-type
              data: {
                content: `This is the message`,
                embeds: songs.map((song) => ({ // embed is optional, just send content only if you want to
                  title: `This is top text of the embed`,
                  description: `This is directly below\nAnd it can be multiline`,
                  fields: song.difficulties.map((difficulty) => ({
                    name: "This will be bold",
                    value: `This is below the bold text`,
                  })),
                  image: {
                    url: "image url here",
                  },
                  url: `Hyperlink for the title of your embed`,
                })),
              },
            })
        default:
            response.status(400).end("Unknown command");
    }
}

Deploy to Vercel

Nothing special here, just do these steps:

Make sure your code is on GitHub, PLEASE MAKE SURE YOU DON’T PUSH YOUR CREDENTIALS
Create a new project in Vercel
Set up environment variables for your bot

Make sure Discord hits your Vercel project

If you go to your Discord applications detail, there should be a Interactions Endpoint URL on the General Information section. Put your vercel project URL there but append /api to it. If everything is set up properly, it should be good to go.

Conclusion

Now you too can create your own serverless Discord bot in Vercel. You can go as crazy as you want, as long as it is using Node.js (or Go or Python or Ruby if you want to still use Vercel’s runtime).

Render can host your API for free
Supabase has a free PostgreSQL instance
MongoDB has its own cloud provider, called MongoDB Atlas
Firebase can also store data, in theory it should work
I recommend looking around this resource for free tier services

The theory#

Setting up your bot#

Registering your slash command(s)#

Creating the serverless bot#

Verify if incoming requests are from Discord or not#

Respond to pings#

Respond to slash commands#

Deploy to Vercel#

Make sure Discord hits your Vercel project#

Conclusion#