LangChain Social Media: Post from a LangChain Agent

Why Posta + LangChain?

Path 1 — Posta MCP via langchain-mcp-adapters (recommended)

The langchain-mcp-adapters package converts MCP servers into LangChain tools. Load the Posta server once and every Posta capability is available to your agent.

pip install langchain-anthropic langchain-mcp-adapters langgraph

# agent.py
import os
from langchain_anthropic import ChatAnthropic
from langchain_mcp_adapters.client import MultiServerMCPClient
from langgraph.prebuilt import create_react_agent

async def main():
    client = MultiServerMCPClient({
        "posta": {
            "command": "npx",
            "args": ["-y", "posta-mcp"],
            "env": {"POSTA_API_TOKEN": os.environ["POSTA_API_TOKEN"]},
            "transport": "stdio",
        }
    })
    tools = await client.get_tools()
    agent = create_react_agent(ChatAnthropic(model="claude-sonnet-4-6"), tools)

    result = await agent.ainvoke({"messages": [
        ("user", "Draft and schedule a LinkedIn post about our new release for tomorrow 9am CET.")
    ]})
    print(result)

Path 2 — Wrap the REST API as a LangChain Tool

For deterministic chain steps where you don't need the agent to choose between tools, the REST API is simpler. One Tool, one POST.

from langchain_core.tools import tool
import os, requests

POSTA = "https://api.getposta.app"
HEADERS = {"Authorization": f"Bearer {os.environ['POSTA_API_TOKEN']}"}

@tool
def schedule_post(
    caption: str,
    social_account_ids: list[int],
    scheduled_at: str,
    media_ids: list[str] | None = None,
) -> dict:
    """Create a draft on the given social accounts, then schedule it.
    scheduled_at is an ISO 8601 timestamp. media_ids are Posta media IDs."""
    # Step 1 — create draft
    r = requests.post(
        f"{POSTA}/v1/posts", headers=HEADERS, timeout=30,
        json={
            "caption": caption,
            "socialAccountIds": social_account_ids,
            **({"mediaIds": media_ids} if media_ids else {}),
        },
    )
    r.raise_for_status()
    post_id = r.json()["id"]
    # Step 2 — schedule it
    r = requests.post(
        f"{POSTA}/v1/posts/{post_id}/schedule", headers=HEADERS, timeout=30,
        json={"scheduledAt": scheduled_at},
    )
    r.raise_for_status()
    return r.json()

Common patterns