The button in the ribbon you never clicked
There is a Get Add-ins button sitting in the ribbon of Word, Excel, Outlook, and PowerPoint, and most people have never touched it. Then a colleague mentions an add-in that logs emails to their CRM, or checks grammar as they type, or builds a report at the press of a button, and the question surfaces: what are Office add-ins, exactly? The short version is that an Office add-in is a small app that lives inside an Office application and adds features Microsoft did not build in. This guide explains what they are in plain language, the types that exist, how they work behind the scenes, where to get them, whether they are safe to use, and what is involved if you want a custom one built for your own workflow.
Key Takeaways
An add-in is an app inside Office
It adds buttons, panels, and features to Word, Excel, Outlook, PowerPoint, and OneNote that are not part of the app by default.
Modern add-ins are web apps
They are built with web technology and run in a small sandboxed panel inside Office, so the same add-in works on Windows, Mac, and the web.
There are a few types
Task pane add-ins open a side panel, content add-ins sit inside a document, and command add-ins add ribbon buttons.
You get them from the store or your admin
Public add-ins come from the Office Store (AppSource); company add-ins are deployed by an administrator; custom ones are built to order.
They run in a safe sandbox
Add-ins cannot freely access your machine, and public ones are reviewed by Microsoft before they reach the store.
You can build your own
When no existing add-in fits your workflow, a custom add-in puts your exact process inside Office.
What is an Office add-in?
An Office add-in is a small application that runs inside a Microsoft Office app such as Word, Excel, Outlook, or PowerPoint, adding features that are not built in. Modern Office add-ins are web applications built with HTML, CSS, and JavaScript that run in a sandboxed panel inside the app, which lets the same add-in work across Windows, Mac, and the web.
Think of Office as a house and add-ins as appliances you plug in. The house comes with the essentials, and add-ins let you bolt on extras the builder never included: a grammar checker in Outlook, a live data feed in Excel, a contract assembler in Word, a slide generator in PowerPoint. They extend what the app can do without you switching to a different program.
Under the surface, a modern Office add-in is a web app. It is made of the same web technologies as a website, hosted on a server, and Office loads it into a small panel inside the application. Because it is web-based, one add-in runs across Office on Windows, Mac, and the browser. This is the model Microsoft now uses across the suite, and it is why add-ins feel consistent wherever you open them.
People sometimes call these plugins, extensions, or add-ons. In the Office world the official term is add-in, and in 2026 it almost always means the modern web kind described here, rather than the older desktop technology covered further down.
What are the different types of Office add-ins?
Add-ins come in a few shapes depending on how they appear in the app.
Task pane add-ins. The most common type. They open a panel along the side of the document or email where you interact with the add-in: enter settings, run an action, review results. A CRM logging tool or a report builder usually lives here.
Content add-ins. These embed inside the document itself rather than off to the side, often used in Excel to show a custom visualisation or interactive element right on the sheet.
Command add-ins. These add buttons to the ribbon or to menus, so you can trigger an action with one click without opening a panel. Many add-ins combine a ribbon button with a task pane.
You can also group add-ins by which app they extend: Outlook add-ins for mail and calendar, Excel add-ins for spreadsheets, Word add-ins for documents, PowerPoint add-ins for presentations, and OneNote add-ins for notebooks. Each host has its own capabilities, which is why an add-in built for one app does not automatically work in another.
How do Office add-ins actually work?
Two pieces make an add-in: the web app and the manifest. The web app is the code that does the work, hosted on a server somewhere. The manifest is a small configuration file that tells Office where that web app lives, what buttons to add, and what permissions the add-in needs. When you install an add-in, Office reads the manifest, adds the buttons it describes, and loads the web app into a panel when you open it.
The add-in talks to the document through a programming interface called the Office JavaScript API, often shortened to Office.js. That is how an add-in reads the email you are looking at, writes values into a spreadsheet, or inserts text into a document. If you are curious about that layer, our field guide to Office.js explains it in more depth.
Crucially, the add-in runs in a sandbox, a fenced-off area that cannot freely reach your files or other programs on your computer. That boundary is deliberate. It keeps a misbehaving add-in from harming your machine and is a big part of why add-ins are safer than the old desktop plugins.
How are add-ins different from the old plugins?
If you have used Office for many years, you may remember add-ins that installed directly onto your Windows machine and could do almost anything on it. Those are COM add-ins, and the related VSTO add-ins, built with desktop technology rather than the web. They are powerful but tied to Windows, and they do not run on Mac, on the web, or in the new Outlook.
The modern web add-in is the replacement. It gives up the deep machine access of the old plugins in exchange for working everywhere and being far safer and easier to manage. Microsoft is steering the whole platform toward web add-ins, which is why new add-ins are built this way. We cover the older technology in our explainer on what a COM add-in is, if you have run into one and wondered what it was.
For a normal user, the practical takeaway is simple: the add-ins you install from the store today are the modern, safe, cross-platform kind, and the ones that worried IT departments years ago were a different, older breed.
Where do you get Office add-ins, and how do you install one?
You get Office add-ins from the Office Store (Microsoft AppSource) through the Get Add-ins or Add-ins button in the ribbon, from your organisation's administrator who can deploy add-ins to your account, or as a custom add-in built specifically for you. To install a store add-in, open Get Add-ins, search, and select Add.
There are three routes. The first is the Office Store, also called AppSource. In Word, Excel, PowerPoint, or Outlook, look for the Get Add-ins or Add-ins button, which opens a panel where you can search the store, pick an add-in, and add it. It installs and appears in your ribbon, and because you signed in with your Microsoft account, it follows you across your devices.
The second route is your administrator. In a company, IT can deploy add-ins centrally so they appear for staff automatically, with no store visit needed. This is how businesses roll out internal tools and approved third-party add-ins.
The third route is custom. When no existing add-in does what you need, one is built to order and either deployed by your admin or published to the store. That is the path for company-specific workflows, which is most of what we build at Orfys.
If you have looked through the store and nothing quite fits the way your team actually works, that is the moment a custom add-in earns its place. We build add-ins that put your specific process, your data, and your systems directly inside Office. See the kind of work we do on our page, and we will tell you honestly whether a custom build or an existing add-in is the smarter call.Office Add-in development services
What can Office add-ins do? Real examples
The range is wide, but a few examples show the pattern.
In Outlook, add-ins log emails to a CRM, check messages before they send, translate mail, and surface customer information next to a message. Our guide to Outlook add-in development goes deeper here.
In Excel, add-ins pull live data from databases and APIs, add custom formulas, automate reports, and run analysis tailored to a business. The Excel add-in development guide covers what is possible.
In Word, add-ins assemble contracts from clause libraries, enforce house style, and draft or proofread with AI.
In PowerPoint, add-ins build slides from data, enforce brand templates, and generate first-draft decks.
Across all of them, AI features have become common: drafting, summarising, classifying, and translating, with the heavy lifting done by a service behind the add-in. The unifying idea is that an add-in brings an outside capability or an outside system into the app where you already work, so you stop switching tools.
Are Office add-ins safe, and are they free?
On safety, the design works in your favour. Add-ins run in a sandbox that cannot freely access your computer, and any add-in in the public store has passed Microsoft's review, which checks things like secure connections and a valid privacy policy before the add-in is allowed in. That is a meaningfully higher bar than the old desktop plugins ever had to clear. As with anything, use add-ins from publishers you trust and pay attention to the permissions an add-in requests, but the platform itself is built to contain them.
On cost, it varies. Many add-ins are free, some are free with paid upgrades, and some are paid or subscription-based, often billed through the publisher rather than Microsoft. Company-deployed and custom add-ins are simply part of whatever your business arranges. There is no single answer, but you will see the pricing before you commit to anything in the store.
Office add-in types at a glance
| Type | Where it appears | Typical use |
|---|---|---|
| Task pane | A panel beside the document or email | Settings, actions, results (CRM, reports) |
| Content | Embedded inside the document | Custom visuals or interactive elements |
| Command | Buttons on the ribbon or menus | One-click actions |
| Mail (Outlook) | Reading or composing an email | Logging, compliance, translation |
Frequently asked questions
What is an Office add-in in simple terms?
It is a small app that runs inside an Office program like Word, Excel, or Outlook and adds features that are not built in, such as a grammar checker or a CRM logger. Modern add-ins are web apps that run in a panel inside the app and work across Windows, Mac, and the web.
How do I install an add-in in Office?
In Word, Excel, PowerPoint, or Outlook, open the Get Add-ins or Add-ins button in the ribbon, search the store, and select Add. The add-in installs and appears in your ribbon, and because it is tied to your Microsoft account, it follows you across devices.
Are Office add-ins safe to use?
Generally yes. They run in a sandbox that cannot freely access your computer, and add-ins in the public store pass a Microsoft review that checks secure connections and a privacy policy. As always, use add-ins from publishers you trust and review the permissions they request.
Are Office add-ins free?
It depends on the add-in. Many are free, some are free with paid upgrades, and some are paid or subscription-based, usually billed by the publisher. You will see the pricing before you install anything from the store. Company-deployed and custom add-ins are arranged by your business.
What is the difference between an add-in and a plugin?
People use the words interchangeably, but in Office the official term is add-in. Modern add-ins are web apps that work across platforms. The older desktop plugins, called COM or VSTO add-ins, install on Windows only and are being phased out in favour of the web model.
Can I get a custom add-in built for my business?
Yes. When no existing add-in fits your workflow, a custom add-in puts your exact process, data, and connected systems inside Office. It is then deployed by your administrator or published to the store, and it works across the platforms its features support.
Small apps, big time savings
Office add-ins are one of the more useful and least understood parts of Microsoft 365. They are small apps that live inside Word, Excel, Outlook, PowerPoint, and OneNote, built on web technology so they run wherever you do, and contained in a safe sandbox so they cannot run wild on your machine. You get them from the store, from your IT department, or as a custom build, and they exist to bring an outside capability into the app you already use so you stop hopping between tools. If your team has a workflow that no off-the-shelf add-in quite covers, that is exactly where a custom one pays off. Tell us what your people do by hand and we will show you what an add-in could take off their plate. Reach out through our contact page anytime.