Mastra Social Media: Posta MCP & Tools for Mastra Agents

Why Posta + Mastra?

Path 1 — Posta MCP via Mastra MCPClient (recommended)

Mastra's MCP client loads any MCP server's tools and exposes them as a toolset on your Agent.

npm i @mastra/core @mastra/mcp @ai-sdk/anthropic

// src/mastra/index.ts
import { Mastra } from '@mastra/core/mastra'
import { Agent } from '@mastra/core/agent'
import { MCPClient } from '@mastra/mcp'
import { anthropic } from '@ai-sdk/anthropic'

const mcp = new MCPClient({
  servers: {
    posta: {
      command: 'npx',
      args: ['-y', 'posta-mcp'],
      env: { POSTA_API_TOKEN: process.env.POSTA_API_TOKEN! },
    },
  },
})

const publisher = new Agent({
  name: 'social-publisher',
  instructions: "Draft and schedule social posts. Match each platform's voice.",
  model: anthropic('claude-sonnet-4-6'),
  tools: await mcp.getTools(),
})

export const mastra = new Mastra({ agents: { publisher } })

// later:
const res = await publisher.generate(
  'Draft a LinkedIn post and a Bluesky post about our v2 launch and schedule both for tomorrow 9am CET.'
)
console.log(res.text)

Path 2 — createTool() around the REST API

Use when you want one deterministic call exposed to the agent — no MCP transport, no tool discovery.

import { createTool } from '@mastra/core/tools'
import { z } from 'zod'

const POSTA = 'https://api.getposta.app'
const headers = () => ({
  'Authorization': `Bearer ${process.env.POSTA_API_TOKEN}`,
  'Content-Type': 'application/json',
})

export const schedulePost = createTool({
  id: 'schedule-post',
  description: 'Create a Posta draft on the given social accounts and schedule it. scheduledAt is ISO 8601.',
  inputSchema: z.object({
    caption: z.string(),
    socialAccountIds: z.array(z.number()),
    scheduledAt: z.string(),
    mediaIds: z.array(z.string()).optional(),
  }),
  outputSchema: z.object({ id: z.string(), scheduledAt: z.string() }),
  execute: async ({ context }) => {
    // Step 1 — create the draft
    const createRes = await fetch(`${POSTA}/v1/posts`, {
      method: 'POST',
      headers: headers(),
      body: JSON.stringify({
        caption: context.caption,
        socialAccountIds: context.socialAccountIds,
        ...(context.mediaIds?.length ? { mediaIds: context.mediaIds } : {}),
      }),
    })
    if (!createRes.ok) throw new Error(`Posta create ${createRes.status}`)
    const { id } = await createRes.json()

    // Step 2 — schedule it
    const scheduleRes = await fetch(`${POSTA}/v1/posts/${id}/schedule`, {
      method: 'POST',
      headers: headers(),
      body: JSON.stringify({ scheduledAt: context.scheduledAt }),
    })
    if (!scheduleRes.ok) throw new Error(`Posta schedule ${scheduleRes.status}`)
    return { id, scheduledAt: context.scheduledAt }
  },
})

Common patterns