posterly

MCP connector

Slack MCP server

Post to Slack channels from Claude or ChatGPT, as the posterly app or as yourself.

This is the posterly MCP server, used for Slack. The same connection works from Claude, ChatGPT, Cursor, and other MCP clients. It is not a separate Slack-only download.

Get Starter + API · $10/moHow to connect the MCP server

What you can do on Slack

Connect a Slack workspace with the standard Add to Slack flow, choose the public or private channels you want, and each channel becomes its own connected account. Your AI client can then post text up to 3,000 characters, images, videos, and groups of up to 10 files, each up to 10 MiB.

Messages can be sent as the posterly app or, after you grant user posting access, as yourself. For richer layouts the assistant can send Slack markdown or Block Kit blocks. When a public channel needs it, posterly joins the channel automatically. File uploads depend on your workspace policy. Ask Claude to draft in the tone your team already uses, then approve the preview before it sends.

It works well for scheduled updates to a team or a customer community: a Monday plan, a release announcement, or a weekly digest drafted by Claude and sent to the right channel at the right time. The MCP server posts to Slack but does not read channels or analytics.

  • Text posts
  • Images
  • Video
  • Multi-image

Post types: text, image, video, carousel. Analytics are not read for this platform.

Tools

These are the tools your AI client uses for Slack. Ask it to call list_platforms with view=schema and the account_id before it sets anything specific to Slack.

Account and connection

  • whoamiWho am I

  • list_accountsConnected accounts

  • list_platformsPlatforms

  • create_connect_sessionStart a connect session

Posts

  • validate_postValidate a post

  • create_postCreate a post

    Show the caption, account, and time, then wait for confirmation before confirm=true.

  • create_posts_batchCreate posts in bulk

    1 to 25 posts in one confirmed request.

  • update_postEdit a post

    Show the caption, account, and time, then wait for confirmation before confirm=true.

  • list_postsPosts

  • get_postOne post

  • delete_postDelete posts

    Live removal needs an eligible connection and confirm_published. A refusal keeps the posterly record.

  • find_available_slotFind a free slot

  • generate_captionsGenerate captions

Media

  • upload_mediaUpload media

    Hosted requests are about 4MB, so this path is for small files. Large files use create_signed_upload or create_media_drop.

  • create_signed_uploadSigned upload link

  • create_media_dropMedia drop link

  • list_mediaMedia library

How to connect

  1. Add the hosted server in Claude, ChatGPT, Cursor, or another MCP client. Server URL: https://www.poster.ly/api/mcp. Sign in with posterly OAuth and press Allow. Use the www host. In ChatGPT, write actions need a Business, Enterprise, or Edu plan.
  2. Or, in a client that can run a local process (Cursor, Claude Code, Windsurf, and similar), use npx -y posterly-mcp-server@latest with a POSTERLY_API_KEY placeholder in that client's MCP config.
  3. Call whoami and list_accounts so you know which workspace the client is using.
  4. Connect Slack with the method below, then call list_platforms with view=schema and the account_id.

Slack

Ask your AI client to start a connection, open the link it gives you, and approve access on the platform.

  • After install, pick one or more channels; each channel becomes a connected account.
Connect Slack in the dashboard

Example prompts

  • Post the weekly priorities to #team-updates on Slack on Monday at 9am, with a short bulleted list and the sprint board link.
  • Send this release note to #customers on Slack on Thursday at 2pm with the screenshot attached.
  • Schedule a Block Kit announcement in #general for the company all-hands on Friday morning.

Slack limits

Caption or text
3,000 characters.
Media count
Up to 10 media items. Up to 10 images.

Request rates depend on your plan. The posterly MCP page lists them.

Pricing

API and MCP access is an add-on to any posterly plan. Starter plus API is $10 a month, charged now with no free trial on this checkout.

Get Starter + API · $10/moSee every plan

FAQ

What is the Slack MCP server?

It is the posterly MCP server, not a separate product. Connect it once and the same connection covers Slack and 17 other platforms, from Claude, ChatGPT, Cursor, and other MCP clients.

How do I connect Slack?

Add the hosted server at https://www.poster.ly/api/mcp and sign in with posterly, or run npx -y posterly-mcp-server@latest in a client that can start a local process. Slack: Ask your AI client to start a connection, open the link it gives you, and approve access on the platform.

Can Claude post to private Slack channels?

Yes. After you add posterly to your workspace you pick the channels you want, public or private, and each one becomes a connected account. For public channels posterly can join automatically when it needs to. A private channel needs the posterly bot invited to it first, using /invite in that channel.

Can Slack messages come from me instead of the posterly app?

Yes. Turn on posting as yourself in the Slack settings in posterly after you grant user posting access, and messages go out as you. It is a setting on the connection rather than a choice per post, and otherwise the app sends them.

Keep reading

MCP

posterly MCP server

Hosted OAuth setup, the local npm package, and the full tool list.

Scheduler

Slack scheduler

Schedule Slack from the posterly calendar and composer.

Guide

Slack guide

Read the long Slack guide, then come back to connect it.

Pricing

posterly pricing

Compare plans, then add API and MCP at checkout.

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