The Best Substack Extensions 2025

Tools for Substack to Extend the Capabilities & Workflow

May 22, 2025

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Intro

Substack is simple on purpose — and that’s part of what makes it great.

But if you’re publishing regularly, trying to grow your audience, want more control over how things look and work, or need extended capabilities, there are a few tools and extensions worth knowing about.

Here’s a short list of helpful add-ons that can make your newsletter workflow easier, more flexible, and a little more professional.

1. SubstackAPI.com

This site offers a few handy tools for Substack. The main one (and the one I used for a long time) is the subscribe form to add to any website.

As you may know, Substack does offer an official subscription form that you can get in the settings of your Substack publication and add to your website. It’s a simple iframe. And that's the problem. You can’t do much with it. You can’t change the design, form function, or anything really. And it doesn’t look great at all.

That’s where substackapi.com comes in. Here, you can create a customizable and stunning, yet simple embed form for your Substack to use on your websites. It’s easy to do, and you simply need to paste the code to your website at the end. It also works flawlessly.

Why it’s useful:

Substack may be your newsletter and blog outlet, but you may have a separate website or blog as your home base. Sending potential subscribers from this homepage to your Substack publication is usually a multistep process, and you’ll lose people along the way. With this simple embed form, you can make subscribing a single step process from anywhere.

2. Sidestack.io*

Substack isn’t Gumroad or Etsy. It’s for writing.

But many writers do sell stuff. Courses, products, services. Whatever it is, you can use Gumroad and other platforms to create and host products, and link to those within your Substack. That's one option. Or you can use Sidestack.io.

This handy little tool lets you create and host products to link to on Substack in an easy and well-designed way that looks a lot like a native Substack tool.

Why it’s useful:

Don’t bother with separate platforms if you just want to sell (or give away) a few products. Sign up for Sidestack.io* (for free), connect to Stripe, and sell your stuff on Substack in what feels like a native extension.

3. SubstackTools.com

Less a tool, more a resource hub. It collects guides, comparisons, and tips for Substack writers. But it also offers a few simple but useful tools. Like an enhanced search for Substack, a discover engine, a shareX tool that creates shareable links to your posts for X, and a downloader to read Substack posts offline.

Why it’s useful:

You might want to share your issues on X, but Elon doesn’t like links that take you off X. So, X doesn’t play nice with Substack links. ShareX solves this. The other tools are helpful as well.

4. Substack Notes Scheduler*

A browser extension that lets you schedule Substack Notes* in advance. You can’t do that natively. This tool was developed by Finn Tropy and it’S a pretty cool extension for Substack Notes. Finn also offers some other tools on his Gumroad page*. It’s worth checking out.

Why it’s useful:

Sometimes, your greatest Notes ideas come in the middle of the night. To avoid posting right there and then, schedule your Note to go live the next morning. Simple but powerful.

5. Substack Messaging Extension (Chrome Web Store)

An unofficial tool that allows you to send direct messages to batches of your subscribers. Now, I don’t use this. I don’t want to get spammy. But for some, this can be a very useful extension for Substack.

Why it’s useful:

If you want to send a short note to new paid subscribers, or reach out to a specific segment of your audience, this tool can help. Just be careful — it’s not officially supported, and misusing it could affect your email deliverability, not to mention your reputation.

The Bottom Line

None of these tools are essential — Substack works just fine on its own.

But if you’ve reached a point where you want more control, better forms, or helpful additions, these are worth exploring. Pick what fits your workflow and leave the rest.

Simple as that.