Using MCP Servers in ChatGPT: Developer Mode + Apps SDK
ChatGPT supports MCP now — the same open protocol Anthropic introduced in late 2024 — which means the same servers that power Claude can power ChatGPT. This guide walks through enabling Developer Mode, connecting a custom MCP server, and using Apps SDK integrations, with Carly as the working example. If you’ve been waiting for ChatGPT to catch up on tool use, this is it.
Looking beyond ChatGPT? MCP servers by category covers the rest.
What ChatGPT’s MCP support actually does
MCP is a standard for letting an AI client call external tools — calendar, CRM, GitHub, your internal database, anything. ChatGPT can now connect to MCP servers and call those tools mid-conversation, which is what Claude has been doing in Claude Desktop and Claude Code for over a year. The one meaningful difference: ChatGPT only supports remote MCP servers — HTTPS endpoints you connect to over the network. It doesn’t support local stdio servers (the node my-server.js kind that Claude Desktop and Cursor run on your laptop). So you either need a hosted MCP endpoint, or you need to expose a local server as a remote one with a bridge like mcp-remote.
Plan availability
Custom MCP connectors live behind ChatGPT’s Developer Mode, which is available on Plus, Pro, Team, Enterprise, and Edu plans. Free ChatGPT does not support custom connectors. Apps SDK is the separate, developer-facing path: it’s how teams build integrations that show up in ChatGPT’s official app catalog for any user to install — no Developer Mode required on the user side. If you’re a builder, OpenAI’s MCP docs cover both paths and the Apps SDK examples repo has working code.
Two ways to connect
There are two flavors of “MCP in ChatGPT” and they get conflated all the time:
- Custom Connectors / Developer Mode — for individuals adding an MCP server to their own ChatGPT account. You paste in a URL, OAuth or paste a token, and the tools show up in your chats. Good for personal workflows and trying servers nobody has packaged yet.
- Apps SDK — for developers publishing an MCP-backed integration that any ChatGPT user can install from the app catalog. Apps SDK uses MCP under the hood but adds UI components, OAuth scaffolding, and review/distribution.
We’ll walk through Custom Connectors first because that’s what most people are searching for.
Step-by-step: enable Developer Mode in ChatGPT
- Open ChatGPT (web or desktop).
- Click your profile picture → Settings.
- Go to Connectors.
- Click Advanced at the bottom.
- Toggle Developer mode on.
You’ll get a warning that custom connectors run third-party code on your behalf. Read it, accept it, and you’re in. A new Add custom connector button appears in the Connectors panel.
If you don’t see the Advanced section, double-check you’re on Plus or higher and that your workspace admin (on Team/Enterprise) has allowed Developer Mode.
What MCP still won’t do for you
Once you have connectors working, the ceiling becomes obvious fast: MCP is request-response. You ask, a tool answers. Nothing in an MCP server can start a conversation.
That means the jobs people actually want automated stay manual. “When a customer replies, draft the follow-up and send it.” “When the deploy goes red, tell the on-call engineer.” “Every Friday, pull the numbers and email the summary.” None of those are expressible in MCP, because MCP has no way to notice anything happened.
MCP has no trigger mechanism and no scheduler. Its own Triggers and Events working group opens by conceding that clients learn about server-side changes by polling, and that work is still listed as on the horizon rather than shipped.
That gap is what Carly is built for, and it’s worth being precise about how the two relate.
Carly does publish an MCP server, but it’s deliberately narrow: it scopes to booking pages and the bookings made through them — create a booking link, change its availability rules, list who booked. It doesn’t read your calendar, and it isn’t where Carly’s value is. The install guide for Claude Code, Claude Desktop, Cursor, Windsurf, Zed, and VS Code is in the Carly MCP post.
Carly’s actual product is the layer MCP doesn’t cover:
- Workflows that fire on events — an email arrives, a form is submitted, a record changes, a schedule hits, and the work runs. No one has to open a chat.
- It sends, rather than drafts — real email through Gmail and Outlook, from your address, with attachments.
- Multi-step across apps — one trigger can update a CRM, book a calendar slot, post to Slack, and reply to the customer as a single flow.
- Agents with their own email addresses — you can CC one on a thread and it participates, rather than you copying output out of a chat window.
- Free plumbing — Zapier-style workflow steps that don’t use AI run free and unlimited, and AI agents start at $35/month.
So the honest framing: use MCP connectors to give ChatGPT reach inside a conversation. Use Carly for the work that has to happen when you aren’t in one.
Best MCPs to try in ChatGPT right now
Most of the MCP servers worth using in ChatGPT today are ones that already publish hosted/remote endpoints. A starting set:
- Cloudflare — official remote MCP servers for Workers, R2, KV, and observability. Hosted by Cloudflare.
- Stripe — official Stripe MCP server for payments, customers, invoices.
- Linear — official Linear MCP server, OAuth-based, great for “what’s blocking my team this week.”
- GitHub — GitHub’s hosted MCP server covers issues, PRs, code search.
- Notion, Asana, Intercom, Sentry — all ship official remote MCP servers in 2025–2026; pull the URLs from each vendor’s docs.
For a wider catalog, see the official MCP server registry. And for the protocol itself, what is MCP? covers the architecture without the install commands.
Limitations and gotchas
A few things will trip you up:
- No local stdio servers. If a server’s setup says
command: "node"orcommand: "npx", ChatGPT can’t run it directly. Bridge it withmcp-remoteor wait for a hosted version. - OAuth happens inside ChatGPT. Servers that use OAuth will prompt you in a popup the first time. Make sure popups aren’t blocked, and re-auth if your token expires.
- Tools aren’t available in shared chats. Custom connectors are scoped to your account. If you share a conversation, the recipient won’t be able to re-run the tool calls.
- Rate limits apply. ChatGPT enforces its own per-tool rate limits on top of whatever the MCP server enforces. High-volume agentic loops will hit ceilings faster than they would in Claude Code.
- Team/Enterprise admin controls. On Team and Enterprise plans, admins can disable Developer Mode org-wide or allowlist specific connectors. If your toggle is missing, it’s likely a workspace policy.
- Apps SDK ≠ Custom Connectors. If you’re trying to publish a connector for other people to use, you want Apps SDK and its review process — pasting your URL into a friend’s ChatGPT works, but it’s not how you ship to the catalog.
For installing MCP in Claude, Cursor, or Windsurf instead, see the install guide.
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