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Cast Action

We’ll also validate the requests using Neynar’s frame validator which provides analytics as well! Before we begin, you can access the complete source code for this guide on GitHub. Let’s get started!

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Creating a new frames project

We will use bun and frog for building the cast action in this guide, but feel free to use framejs, onchainkit, or anything else as well! Enter this command in your terminal to create a new app: 
bunx create-frog -t bun
Enter a name for your project and it will spin up a new project for you. Once the project is created install the dependencies: 
cd <project_name>
bun install
Now, let’s install the dependencies that we are going to need to build out this action: 
bun add @neynar/nodejs-sdk dotenv

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Creating the cast action route

Head over to the src/index.ts file. Here, you’ll be able to see a starter frame on the / route. But first, let’s change the Frog configuration to use /api as the base path and use neynar for hubs like this: 
export const app = new Frog({
  hub: neynar({ apiKey: "NEYNAR_FROG_FM" }),
  basePath: "/api",
});
You also might need to import neynar from “frog/hubs”: 
import { neynar } from "frog/hubs";
Now, we’ll create a new post route which will handle our cast actions. So, create a new route like this: 
app.hono.post("/followers", async (c) => {
  try {
    let message = "GM";
    return c.json({ message });
  } catch (error) {
    console.error(error);
  }
});
This route will return a GM message every time the action is clicked, but let’s now use the neynar SDK to get the follower count of the cast’s author! Create a new src/lib/neynarClient.ts file and add the following: 
import { NeynarAPIClient, Configuration } from "@neynar/nodejs-sdk";
import { config } from "dotenv";
config();

if (!process.env.NEYNAR_API_KEY) {
  throw new Error("Make sure you set NEYNAR_API_KEY in your .env file");
}
// make sure to set your NEYNAR_API_KEY .env
// don't have an API key yet? get one at neynar.com
const configuration = new Configuration({
  apiKey: process.env.NEYNAR_API_KEY,
});

const neynarClient = new NeynarAPIClient(configuration);

export default neynarClient;
Here, we initialise the neynarClient with the neynar api key which you can get from your dashboard:
Neynar API key
Add the api key in a .env file with the name NEYNAR_API_KEY. Head back to the src/index.tsx file and add the following in the followers route instead of the GM message: 
try {
  const body = await c.req.json();
  const result = await neynarClient.validateFrameAction({
     messageBytesInHex:body.trustedData.messageBytes}
  );

  const { users } = await neynarClient.fetchBulkUsers({
   fids: [Number(result.action.cast.author.fid)],
  });

  if (!users) {
    return c.json({ message: "Error. Try Again." }, 500);
  }

  let message = `Count:${users[0].follower_count}`;

  return c.json({ message });
} catch (e) {
  return c.json({ message: "Error. Try Again." }, 500);
}
Here, we use the neynar client that we just initialised to first validate the action and get the data from the message bytes. Then, we use it to fetch the user information using the fetchBulkUsers function. Finally, we return a message with the follower count!

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Creating a frame with add cast action button

I am also adding a simple frame that allows anyone to install the action. But for that, you need to host your server somewhere, for local development you can use ngrok. If you don’t already have it installed, install it from here. Once it’s installed, authenticate using your auth token and serve your app using this command: 
ngrok http http://localhost:5173/
This command will give you a URL which will forward the requests to your localhost:
Ngrok URL
You can now head over to the cast action playground and generate a new URL by adding in the info as such:
Farcaster Cast action playground
Copy the install URL and paste it into a new variable in the index.tsx like this: 
const ADD_URL =
  "https://warpcast.com/~/add-cast-action?actionType=post&name=Followers&icon=person&postUrl=https%3A%2F%2F05d3-2405-201-800c-6a-70a7-56e4-516c-2d3c.ngrok-free.app%2Fapi%2Ffollowers";
Finally, you can replace the / route with the following to have a simple frame which links to this URL: 
app.frame("/", (c) => {
  return c.res({
    image: (
      <div
        style={{
          alignItems: "center",
          background: "black",
          backgroundSize: "100% 100%",
          display: "flex",
          flexDirection: "column",
          flexWrap: "nowrap",
          height: "100%",
          justifyContent: "center",
          textAlign: "center",
          width: "100%",
        }}
      >
        <h2
          style={{
            color: "white",
            fontSize: 60,
            fontStyle: "normal",
            letterSpacing: "-0.025em",
            lineHeight: 1.4,
            marginTop: 30,
            padding: "0 120px",
            whiteSpace: "pre-wrap",
          }}
        >
          gm! Add cast action to view followers count
        </h2>
      </div>
    ),
    intents: [<Button.Link href={ADD_URL}>Add Action</Button.Link>],
  });
});
If you now start your server using bun run dev and head over to http://localhost:5173/dev you’ll be able to see a frame somewhat like this:
Frog frame dev env
Click on Add action and it’ll prompt you to add a new action like this:
Add farcaster action
Once you have added the action, you can start using it on Warpcast to see the follower count of various people! 🥳

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Analytics

Since we are using the validateFrameAction function, we also get analytics out of the box. Head over to the usage tab and click on the frame that you are currently using. It will provide you with various analytics like total interactors, interactions per cast, etc.
Frame analytics

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Conclusion

This guide taught us how to create a Farcaster cast action that shows the follower count of the cast’s author! If you want to look at the completed code, check out the GitHub repository. Lastly, make sure to share what you built with us on Farcaster by tagging @neynar, and if you have any questions, reach out to us on warpcast or Slack!