# How to Post to Social Media with LangChain (2026) · PostLake

> Markdown version of https://postlake.dev/guides/langchain . The canonical page for humans.
> PostLake is the social media API for AI agents: https://postlake.dev/llms.txt

Post to social media with *LangChain*.

Wrap PostLake as one tool, or skip the wrapper and connect MCP. Either way the agent sees the same normalised Post response the Publishing docs describe.

**In short:** One LangChain tool (or MCP) that POSTs /v1/posts. Return the JSON so the agent can read targets[] and decide next steps.

## When this guide is for you

You're building a LangChain agent that should post or schedule without registering nine social tools.

## Before you start

Same setup the [docs quickstart](https://docs.postlake.dev/quickstart.md) uses. Do this once:

- Sign up at [app.postlake.dev](https://app.postlake.dev) and verify your email (unlocks free credits).
- On **Channels**, create a **profile** (e.g. `my-brand`) and connect at least one account. **Bluesky is the fastest first channel**: no app review. Instagram/TikTok/Facebook need each platform's review before API posting.
- Account menu → **API Keys** → create a key (`sk_live_…`). It shows once; treat it like a password.


## Working example in LangChain

Connect accounts once in the dashboard, then this is the publish call:

```
from langchain_core.tools import tool
import os, requests, uuid

@tool
def post_to_social(text: str, platforms: list[str] | None = None) -> dict:
    """Publish via PostLake. Returns the full Post object (check targets[])."""
    body = {"text": text, "profile": "my-brand"}
    if platforms:
        body["platforms"] = platforms  # filter only
    r = requests.post(
        "https://api.postlake.dev/v1/posts",
        headers={
            "Authorization": f"Bearer {os.environ['POSTLAKE_API_KEY']}",
            "Idempotency-Key": str(uuid.uuid4()),
        },
        json=body,
    )
    r.raise_for_status()
    return r.json()

# model.bind_tools([post_to_social]), or use MCP instead (no wrapper)
```

## Step by step

1. Prefer [MCP](https://docs.postlake.dev/mcp) (`https://api.postlake.dev/mcp`) if your LangChain host supports it, OAuth. No key in the tool.
1. Otherwise define one tool that POSTs `/v1/posts` and **returns the full JSON** (not just "ok").
1. Instruct the agent to read `state` and each `targets[].state` before claiming success.
1. Always set `Idempotency-Key` (new UUID per logical post) so tool retries don't double-post.

## Read the response (don't skip this)

You get one `Post` with an overall `state` and a `targets[]` array. One entry per account. **Always check each target**; partial success is normal.

```
{
  "id": "post_a1b2c3",
  "state": "partial",
  "targets": [
    { "platform": "bluesky",  "state": "published", "url": "https://bsky.app/…" },
    { "platform": "linkedin", "state": "failed",
      "error": { "type": "invalid_request", "message": "…", "retryable": false } }
  ]
}
```

- `published`: every target succeeded. `partial`: some published, some failed. `failed`: none published. `processing`: still going (async networks like TikTok).

- **You're only charged for targets that actually publish.** Failed targets cost nothing.

- Send an `Idempotency-Key` header on writes so a retry never double-posts.

- Full detail: [Publishing](https://docs.postlake.dev/publishing) · [Errors & retries](https://docs.postlake.dev/errors)

## Where the post goes

Same rules as the docs. Pick one addressing style:

- **By profile**: `"profile": "my-brand"` posts to every account under that profile (the name on Channels).

- **Filter networks**: `"platforms": ["bluesky", "linkedin"]` narrows that set. It is a **filter, not a selector**: if you have two Pinterest boards, both match `pinterest`.

- **By account id**: `"accounts": ["acc_…"]` for exact channels (copy an id on Channels, or `GET /v1/social-accounts`).

- One profile and you omit `profile`? PostLake uses that profile. Multiple profiles and you omit it? You'll get an error that names them.

See [Publishing: where to post](https://docs.postlake.dev/publishing).

## Do more (same API)

- **Schedule**: add `scheduledAt` as UTC (trailing `Z`), or a naive local time plus `timezone` (IANA, e.g. `Europe/London`). Credits charge when it fires. [Scheduling docs](https://docs.postlake.dev/scheduling) · [scheduling guide](/guides/schedule-posts-api).

- **Media**: `POST /v1/media`, then pass the `med_…` id in `media`. [Media docs](https://docs.postlake.dev/media).

- **Per-network caption**: `textOverrides` (e.g. shorter text for X). **Per-network options**: `platformOptions` (Pinterest `boardId`, TikTok privacy, …). Live option lists: `GET /v1/platforms/{platform}`.

- **Validate first**: `POST /v1/posts/validate` runs the same checks without publishing (free).

## Pitfalls specific to this path

- If the tool returns only a string "posted", the agent cannot handle partial failure, return the Post object.

- Don't give the agent a separate tool per network; one PostLake tool is enough.

- Validate long drafts with `POST /v1/posts/validate` (or the MCP validate tool) before publish.

Want zero wrapper code? Connect the hosted [MCP server](https://docs.postlake.dev/mcp) (`https://api.postlake.dev/mcp`) over OAuth. Same accounts and responses as this API path. [Agents overview](/agents/).

## Common questions

### How do I let a LangChain agent post to social media?

Either connect PostLake MCP, or bind one tool that POSTs /v1/posts with text + profile and returns the JSON. The agent then handles every connected network through that one tool.

### Do I need a tool per social network?

No. One tool calling PostLake covers the profile. Use platforms only as an optional filter.

### Can LangChain use PostLake over MCP?

Yes. Point the host at https://api.postlake.dev/mcp and complete OAuth. Tools for publish, schedule, validate, and analytics appear without a custom wrapper.

## Go deeper in the docs

These guides stay short on purpose. Canonical behaviour lives here:

    [Docs ### Quickstart Account, first channel, first post, MCP or API.](https://docs.postlake.dev/quickstart)
    [Docs ### Publishing Request body, addressing. Partial success, lifecycle.](https://docs.postlake.dev/publishing)
    [Docs ### Scheduling UTC or local time plus timezone, edit/cancel, fire-time credits.](https://docs.postlake.dev/scheduling)
    [Docs ### Platforms Limits, media rules, live platformOptions.](https://docs.postlake.dev/platforms)

Also: [Media](https://docs.postlake.dev/media) · [Errors](https://docs.postlake.dev/errors) · [MCP](https://docs.postlake.dev/mcp) · [Analytics](https://docs.postlake.dev/analytics)

## Related guides

- [Post with CrewAI](https://postlake.dev/guides/crewai.md)
- [Post with AutoGen](https://postlake.dev/guides/autogen.md)
- [Build an AI social agent](https://postlake.dev/guides/ai-social-media-agent.md)
- [Cross-platform analytics](https://postlake.dev/guides/social-media-analytics-api.md)

[All guides](https://postlake.dev/guides/index.md) · [Full docs](https://docs.postlake.dev/) · [llms.txt](https://postlake.dev/llms.txt)

Plain markdown for agents: https://postlake.dev/guides/langchain.md · https://postlake.dev/llms.txt