Substack has always made it easy to take your email list and leave. You can export your subscribers and import them into another platform, and because your payments run through your own Stripe account, you can connect that account elsewhere and keep your paid subscribers. If you use a custom domain, you can take your web address with you as well, pointing it at another host while keeping the links your readers and Google already know.
What you could never do is directly connect Substack to outside tools. There was no official API or developer tooling, so publishers were stuck with messy workarounds to integrate their publication with other platforms. In practice, each of these fixes comes with a catch:
To analyze your own data, you needed to export a CSV and rebuild your charts every time you wanted an update, because whatever analysis tool you set up could not refresh on its own.
To integrate new subscribers with an email automation tool like Kit, you still need to create a Zap that watches your Gmail for Substack’s subscription notifications and adds each new address to Kit, with no way to sync back to Substack when someone unsubscribes through a Kit email.
To manage Notes, you needed to rely on unofficial tools that ran inside your own logged-in browser session, so they only fired while your browser stayed open, and were likely against Substack’s terms of use.
To embed content from another website (Substack only natively supports a few), you still have to upload a screenshot, which can go against other platforms' terms and give readers who use a screen reader, or who want to interact with the content, a worse experience.
Two things changed that recently.
Substack released an MCP server, the first official way to connect your publication’s data to an AI assistant like Claude or ChatGPT.
Substack integrated with Typefully, the first outside social media management tool it has officially supported. (Maybe Buffer will be next!)
I’m surprised neither of these updates has received much attention. For a company that had never opened its platform to outside tools before, doing so twice within a couple of months is a big shift in strategy.
What Is a Walled Garden in Technology?
A walled garden is a closed platform where the company restricts which outside tools can connect to it. The phrase started in cable television, where John Malone of Tele-Communications Inc. is generally credited with it, describing a system where the operator, not the customer, decides which channels reach you.1 In the internet era, the term was first used to describe AOL, which curated the set of services and content its subscribers could access.
Apple runs the best-known walled garden today with the App Store, where it decides which apps are allowed to run on your phone. (Android is more open, since it lets users install apps from outside its store). The opposite approach is a platform that invites outside tools in. WordPress runs on a huge ecosystem of third-party plugins, and Shopify has an entire app store and API that other developers build on.
Walled gardens exist for a reason. They protect the company’s business, and the control makes the experience smoother and safer for users, since everything inside is vetted to work together. The App Store’s tight control is a big part of why iPhones are so hard to infect with malware, and you cannot easily break your Substack the way a WordPress site can break after a plugin update.
You own your subscribers and can leave and take them with you anytime you want, but until now nothing on the outside could connect in.
Let’s take a closer look at what has changed.
Substack’s MCP Server
Substack’s MCP server lets an AI assistant like Claude or ChatGPT read your publication data, but only Bestseller (paid) publications can use it.
What Is an MCP Server?
An MCP server is a connector that lets an AI assistant read data from an outside service in real time. MCP stands for Model Context Protocol, an open standard for linking AI tools to sources of data. When a company builds an MCP server, it gives assistants like Claude and ChatGPT a defined, permission-based way to see specific information and interact with it.
Substack built an MCP server for publications, and once you connect it, your assistant can read your data while you chat, without exporting anything or leaving the conversation.
Really Good Business Ideas runs one too. Premium subscribers can connect it to Claude and access tools and datasets like 200 proven hook templates, a database of what other Substacks offer their paid subscribers, a reader persona builder, and a content style guide creator.
How Substack’s MCP Server Works
Substack’s MCP server lets you give an AI assistant read-only access to your publication data. Once connected, your agent can pull your dashboard metrics, subscriber counts, revenue, retention, traffic sources, and post performance, and it can read your publication settings. It cannot publish a post, send a Note, or change your account, and it has no access to your profile or Notes activity.
The benefit of that access is analysis. Substack’s built-in analytics are limited to a fixed set of dashboard views, and any CSV you export is a static snapshot that goes stale quickly. That makes it difficult to assess your performance in depth or refine your strategy with confidence. With the server connected, your assistant works from live data you can question in plain language, so investigating a growth slowdown becomes a natural part of how you already work rather than a daunting major project. I'll share more about how I use the MCP server in an upcoming post.
MCP server access is limited to admins of paid publications with a Bestseller badge, using an AI client that supports MCP connectors like Claude, ChatGPT, and Cursor. Plenty of software products limit their MCP servers to higher-tier plans, so it is no surprise Substack restricts this one to Bestsellers, given the cost of serving data this way. It’s also probably a strong play, since Bestsellers are more likely to run their publications like businesses and expect a higher level of service. Tools that help them operate more effectively give them a reason to stay.
Substack’s Typefully Integration
Typefully is a social media management tool creators can use to schedule and publish content across platforms from one place. Substack announced Typefully’s integration in August,2 making it the first outside tool of its kind Substack has officially supported. With it connected, you can schedule your Substack Notes ahead of time and cross-post them to X, Threads, LinkedIn, Mastodon, and Bluesky.
In one way, Typefully is the bigger crack in the wall of the two. The MCP server only reads your data, while Typefully acts on your account by scheduling and posting your Notes. Officially letting an outside tool do that is a bigger step for Substack than letting one read your numbers. Personally, I think publishers should be free to choose the tools that work best for them, so I hope we'll see more tools like Buffer get access soon. Plenty of publishers have also built their own Substack-specific tools out of the workarounds available today, so hopefully those get officially supported too.
Will Substack’s Walled Garden Keep Cracking Open?
Substack likely opened the MCP server to Bestsellers because they drive most of its revenue, and their success is essential to Substack’s own. The Typefully integration supports the growth of Substack Notes, which has become a notable social platform in its own right. Both support Substack’s growth and hint at what might come next.
I expect Substack will keep opening up to tools that drive platform growth and help creators become more invested in the platform. An MCP server that can write, not just read, is the obvious next step, since it helps publishers scale and some competitors, like Ghost, already support it.
Conversely, Substack will likely keep its walls up around anything that helps a competitor or encourages readers and revenue to move off the platform. For example, I don’t think we’ll see a Kit integration anytime soon. Substack has spent the past year building deeper segmentation and email automation features that can start to replace Kit, so it’s clear it has decided to solve this limitation internally rather than through external partnerships.
So far, Substack has opened up on tightly controlled terms. The MCP server is limited to read-only access to your own data, and only through an AI tool. Typefully is the only outside social media management partner that can connect to Substack Notes. We still don’t have an open API that anyone can build on, and I don’t expect that to change anytime soon, even as more official integrations arrive. A truly open API would be a much bigger change, since it would let publishers connect any tool they wanted, including a competitor like Kit.
Substack is increasingly building solutions for larger publishers that treat their publications like a business, because they bring in the most revenue and are also the ones most likely to outgrow it and move off the platform. But publishers of all sizes can benefit from most of these features. In fact, these features can make it much easier for a smaller publication to grow into a larger one. Those who start taking advantage of these tools now will benefit most as the platform continues to open up.
To endless possibilities,
Casandra
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