API vs SDK vs MCP: What’s the Difference, and Why It Matters for Marketers

If you’ve spent any time around software in the last year, you’ve probably seen three acronyms thrown around interchangeably: API, SDK, and MCP. They’re related, but they solve different problems and the newest of the three, MCP, is quietly reshaping how marketers will work with tools like email platforms, CRMs, and analytics suites.

Here’s a plain guide to what each one is, how they differ, and why the rise of MCP matters if you’re running marketing campaigns.

The short answer

An API is how two pieces of software talk to each other.

An SDK is a toolkit that makes it easier for developers to build on top of an API.

An MCP is a standard that lets AI assistants use APIs on your behalf, in natural language.

If APIs are the plumbing and SDKs are the wrench, MCP is the assistant who knows how to use both and can do it because you asked with normal words.

What is an API?

API stands for Application Programming Interface. It’s a set of rules that lets one software system request information or actions from another.

When you log into a third-party app using your Google account, that’s an API at work. When your email platform pulls in subscribers from your e-commerce store, that’s an API too. APIs are the connective tissue of the modern internet.

For marketers, APIs matter because they’re what makes integrations possible. Your email tool, your CRM, your analytics dashboard – they all expose APIs so other tools (or your own developers) can read and write data.

The catch: using an API directly requires writing code. It’s powerful, but it’s developer territory.

What is an SDK?

SDK stands for Software Development Kit. It’s a bundle of tools, libraries, and documentation that wraps an API to make it easier to use.

If an API is the raw set of rules, an SDK is the pre-built helper that says “here’s how to do the most common things, without having to figure it out from scratch.” An SDK for an email platform might give a developer ready-made functions for createSubscriber() or sendCampaign() rather than asking them to construct each API request by hand.

SDKs speed up development, but they’re still tools for developers. A marketer can’t use an SDK directly. Usually, they need an engineer to build something on top of it.

What is MCP?

MCP stands for Model Context Protocol. It’s an open standard, introduced by Anthropic in late 2024, that lets AI assistants like Claude connect to external tools and data sources in a consistent way.

Think of MCP as USB-C for AI assistants. Before USB-C, every device had its own plug. Now there’s one standard, and anything that supports it works with anything else that supports it. MCP does the same thing for AI: any AI assistant that supports MCP can talk to any tool that exposes an MCP server.

The crucial difference: MCP isn’t for developers. It’s for end users. A marketer connects their email platform to Claude once, then operates the platform through conversation – no code or clicking through dashboards.

“Create a campaign for our Black Friday offer, target VIP subscribers, use our brand style, and schedule it for Friday at 9am.”

That sentence, in a chat window, becomes a real campaign in your email platform. That’s MCP.

API vs SDK vs MCP: side-by-side

| API | SDK | MCP
What it is | A set of rules for software to communicate | A toolkit that wraps an API for developers | A standard that lets AI assistants use tools
Who uses it | Developers | Developers | End users (marketers, analysts, anyone)
Interface | Code | Code | Natural language
Setup | Custom integration work | Install a library, write code | Connect once, then chat
Example | A REST endpoint that returns subscriber data | A Python library to manage subscribers | "Show me last week's top campaigns" — answered in chat
Best for | System-to-system integration | Speeding up development | Hands-on operation without leaving your AI assistant

Why MCP is a big deal for marketers

For most of software history, the pattern has been: developers build, end users click. If you wanted to do something with your email platform, you either clicked through the UI yourself or asked an engineer to build a custom integration.

MCP changes that. It puts a third option on the table: describe what you want, in plain language, and let the AI do it.

This matters for three reasons:

Speed. Tasks that take ten minutes of clicking become a single sentence. Building a segment, drafting a campaign, pulling a report, it all collapses into a conversation.

Less context-switching. Marketers already use AI assistants for drafting copy, brainstorming subject lines, and summarizing performance. With MCP, the execution happens in the same place as the thinking. No more copy-pasting between Claude and your marketing tool.

Lower technical barrier. You don’t need a developer to build a custom workflow. If you can describe it, the AI can do it.

Does MCP replace APIs and SDKs?

No and that’s an important point.

MCP runs on top of APIs. Behind the scenes, when you ask Claude to create a campaign, the MCP server translates that request into the same API calls a developer would make. The API is still doing the work. MCP is the new layer that lets non-developers tap into it.

So the stack now looks like this:

APIs still power system-to-system communication.

SDKs still help developers build apps and integrations faster.

MCP sits at the top and gives end users a way to operate those systems through natural language.

All three coexist. They serve different audiences and solve different problems.