Build an Autonomous Social Media Bot in One Afternoon

What you'll build

A bot that takes a high-level instruction ("post about our launch this week"), drafts per-platform captions with Claude, schedules them via Posta, and reacts when each post publishes — replying to early comments, pinging Slack, or branching the next campaign step.

The stack

Step 1 — Wire Posta MCP into your client

Get a Posta API token from your dashboard, then add the Posta MCP server to your client's MCP config. The server runs on demand via npx — no separate install step. Restart the client and the Posta tools appear in the tool list.

// claude_desktop_config.json (or your client's MCP config)
{
  "mcpServers": {
    "posta": {
      "command": "npx",
      "args": ["-y", "posta-mcp"],
      "env": { "POSTA_API_TOKEN": "posta_xxx" }
    }
  }
}

Step 2 — Prompt Claude to draft and schedule

With the MCP server wired in, Claude picks the right Posta tool based on the prompt. No prompt-engineered API docs needed.

"This week I'm announcing v2 of our SDK.
 Draft a LinkedIn post (long-form), a Bluesky thread (short),
 and a Threads post. Schedule LinkedIn for Tuesday 9am CET,
 the others for Wednesday 10am CET. Use the launch image from
 my media library."

Claude calls listMedia to find the image, drafts three per-platform captions, and calls createPost three times with the right scheduling. Output ends up in your Posta dashboard as scheduled drafts.

Step 3 — Receive HMAC webhooks

Configure a webhook endpoint in Posta's settings. When a post publishes (or fails), Posta POSTs an HMAC-signed payload to your URL. A minimal receiver in Node:

// webhook.js
import { createHmac, timingSafeEqual } from 'node:crypto'
import express from 'express'

const app = express()
app.use(express.json({ verify: (req, _, buf) => { req.raw = buf } }))

app.post('/posta-webhook', (req, res) => {
  const sig = req.headers['x-posta-signature']
  if (!sig) return res.sendStatus(401)
  const expected = createHmac('sha256', process.env.POSTA_WEBHOOK_SECRET)
    .update(req.raw).digest('hex')
  const sigBuf = Buffer.from(sig)
  const expBuf = Buffer.from(expected)
  if (sigBuf.length !== expBuf.length || !timingSafeEqual(sigBuf, expBuf)) {
    return res.sendStatus(401)
  }

  const { event, platform, platformPostUrl } = req.body
  console.log(`${event} on ${platform}: ${platformPostUrl}`)
  // → trigger next agent action here
  res.sendStatus(200)
})
app.listen(3000)

Step 4 — Close the loop

Now the bot has feedback: each publish fires a webhook, and the receiver can kick off the next action — call Claude back, post a Slack note, branch a multi-day campaign, retry on failure. Some common closed-loop patterns:

Where to go from here

Three good next steps once the basic loop works: