What's the difference between an 'Office plugin' and an 'Office add-in'?

'Plugin' is the old term, usually meaning a Windows-only VSTO/COM add-in. Modern Office add-ins are web apps built on Office.js that run across Windows, Mac, iPad, and the web — that's what I build.

Do you build PowerPoint add-ins?

Yes — as a PowerPoint add-in developer I build slide generation, template automation, and content insertion so decks stay on-brand automatically.

Will the add-in run on Mac and Office on the web?

Yes. Office.js add-ins are cross-platform; I add capability checks where a specific host or platform exposes different APIs.

Can you migrate our old VSTO or COM plugin?

Yes. I move legacy Windows-only plugins to the Office.js web add-in model so they work across platforms and don't break with Office updates.

Are you an experienced Office.js developer?

Yes — Office.js is core to my work across Outlook, Word, Excel, and PowerPoint, including manifests, permissions, and AppSource submission.

Microsoft Office

Office Plugin Development

Custom Office add-ins for Word, Excel, Outlook, and PowerPoint built with Office.js — the modern, cross-platform replacement for old COM/VSTO plugins, running on Windows, Mac, iPad, and the web.

Email me Chat on WhatsApp

What I build

What's included

Add-ins for every Office host

Task panes and ribbon commands for Word, Excel, Outlook, and PowerPoint — often sharing one Office.js codebase across hosts.

PowerPoint add-in development

Slide generation, brand-template automation, and content insertion so decks come out on-brand without manual formatting.

Cross-platform delivery

One add-in that runs on Office for Windows, Mac, iPad, and the web, with graceful checks where a host's API differs.

VSTO / COM migration

Moving legacy Windows-only plugins to the supported Office.js web add-in model so they work everywhere and survive Office updates.

Problems this solves

Sound familiar?

A legacy VSTO/COM plugin that breaks on Office updates and doesn't run on Mac or the web.
Repetitive Office tasks — formatting decks, assembling documents — done by hand daily.
PowerPoint decks that drift off-brand because there's no automation enforcing templates.
Needing the same tool available in more than one Office app.

Example use cases

What this looks like in practice

Branded deck builder

A PowerPoint add-in that turns a short form into a fully branded slide deck using approved templates and layouts.

Clause inserter for Word

A Word add-in that drops approved, formatted clauses into contracts from a central library.

Shared tool across hosts

A single add-in running in both Word and Excel, sharing logic while adapting its UI to each host.

Tech stack

The tools I use for this

Core

Office.js
TypeScript
React

Tooling

Yeoman generator
Unified app manifest

Hosts

Word
Excel
Outlook
PowerPoint

Delivery

Azure Static Web Apps
AppSource
Sideloading

Process

How it works

Pick hosts & scope

Decide which Office apps and what the add-in does in each.

Build with Office.js

Task panes/commands with shared, typed code.

Test cross-platform

Verify on desktop, Mac, and web.

Publish

AppSource or internal deployment with a clean manifest.

This is the overview page. For the two hosts I'm asked for most, see Outlook plugin development and Excel add-in development. It's all part of my broader Microsoft 365 development work.

Related services

FAQ

Questions, answered

What's the difference between an 'Office plugin' and an 'Office add-in'?: 'Plugin' is the old term, usually meaning a Windows-only VSTO/COM add-in. Modern Office add-ins are web apps built on Office.js that run across Windows, Mac, iPad, and the web — that's what I build.
Do you build PowerPoint add-ins?: Yes — as a PowerPoint add-in developer I build slide generation, template automation, and content insertion so decks stay on-brand automatically.
Will the add-in run on Mac and Office on the web?: Yes. Office.js add-ins are cross-platform; I add capability checks where a specific host or platform exposes different APIs.
Can you migrate our old VSTO or COM plugin?: Yes. I move legacy Windows-only plugins to the Office.js web add-in model so they work across platforms and don't break with Office updates.
Are you an experienced Office.js developer?: Yes — Office.js is core to my work across Outlook, Word, Excel, and PowerPoint, including manifests, permissions, and AppSource submission.

Let's build it together

Email me with what you need — I'll reply with a clear plan and next steps. Prefer chat? WhatsApp works too.