ChatGPT social media automation: Actions vs MCP

ChatGPT cannot post to LinkedIn on its own, and neither can Claude. What differs is the plumbing available to fix that. Claude Desktop spawns local processes, so stdio MCP works. ChatGPT runs in a browser, so everything must arrive over HTTPS.

That leaves two routes, both of which work, and which are genuinely different in who they suit.

Route 1 — Custom GPT Actions

This is the route to pick when other people will use the GPT. The key lives in the GPT’s configuration, not in the user’s hands, so you can build “our marketing GPT” and share it with a team that never sees a credential.

1. 1
   Host the server in HTTP mode

   Setting a PORT starts the same npm package as an HTTP service that also serves an OpenAPI 3.0 document at /openapi.json and REST endpoints at /api/tools/:name. Deploy it anywhere that runs Node.

2. 2
   Create the GPT and import the schema

   In the GPT builder, add an Action and import from https://your-host/openapi.json. Every publishing tool arrives as an operation with its parameters already described.

3. 3
   Set authentication

   API key, with the header name Authorization or x-api-key. This is what keeps the credential out of the conversation and out of your users’ hands.

4. 4
   Write the system prompt like an operator, not a poet

   The instructions carry the workflow: always preflight before creating, always confirm copy before publishing, always ask for a timezone when scheduling. Actions have no approval dialog of their own, so the discipline has to live here.

Route 2 — an MCP connection

If you are working solo and already use the same server from Claude or Cursor, MCP gives you one surface everywhere. Tools are discovered rather than pasted, so a server-side change shows up without you re-importing a schema — which matters more than it sounds when a tool gains a parameter.

export POSTMCPAI_API_KEY="pmcp_sec_your_key_here"
export PORT=3000
npx -y @postmcpai/server

# then connect the client to:
# https://your-host/mcp?apikey=pmcp_sec_your_key_here

The server advertises OAuth 2.0 authorization-server metadata and RFC 9728 discovery, which is what remote connectors expect when they register themselves. Setup detail is on the ChatGPT integration page.

Prompts that actually work

Regardless of route, the same three habits separate a GPT that publishes well from one that publishes confidently and wrongly.

• Name the network and the constraint. “LinkedIn, first person, under 1,200 characters, no hashtags” produces a usable draft. “Write a post” produces a press release.
• Ask for a preflight before anything is created. It costs nothing, and it catches the 280-character overflow before Tuesday morning does.
• Say the timezone out loud. Scheduling defaults to UTC. “9am” for an IST account means 14:30 local — a mistake that is invisible until the post appears at lunchtime.

“Draft a launch post for LinkedIn and X. Preflight both. Show me the copy. Do not publish until I confirm.”

That single prompt encodes the whole safe workflow, and it is worth putting verbatim into a Custom GPT’s instructions.

Picking one

Choose Custom GPT Actions if the GPT is for other people, if you want the key held centrally, or if you want a purpose-built assistant with a fixed workflow baked into its instructions.

Choose MCP if it is for you, if you already run the same server in Claude or Cursor, and you want one tool surface rather than two things to keep in sync.

Both write to the same queue, so a post created by a Custom GPT is visible, editable and cancellable in the content calendar like any other. Changing your mind later costs nothing.