Microsoft 365 and Office add-ins
Excel, Word and Outlook add-ins in OfficeJS, VSTO maintenance, and the migration between the two.
A real process runs inside a spreadsheet, and the alternative on the table is replacing it with software nobody wants to use. There is also a fair chance you are maintaining a VSTO add-in your Mac users cannot open at all.
- Starts with
- A 30-minute call
- Timezone
- UTC+05:30 · overlaps EU mornings and US evenings
What you get
- A cross-platform add-in with a signed manifest, working on Windows, Mac and Office on the web.
- A backend API with Entra ID single sign-on, so nobody has to type a second password.
- A centralised deployment your tenant admin installs once for everyone, plus a compatibility note for existing VSTO users.
How it runs
Watch the real workflow
Including the workarounds. The workarounds are the requirements; the documented process usually is not.
Pick the surface
Task pane, ribbon command or custom function — each has different capability and permission limits, and choosing wrong gets discovered late.
Test on all three platforms
OfficeJS behaves differently on Windows, Mac and the browser, which is where the classic failure on the one machine that matters comes from.
Questions
Should we migrate our VSTO add-in to OfficeJS?
If any of your users are on Mac or Office on the web, yes — VSTO cannot reach them at all. If everyone is on Windows desktop and the add-in is stable, the case is much weaker and worth measuring before you spend anything.
Do you handle AppSource publishing?
Including the parts that get submissions rejected: manifest validation, privacy and support URLs, and evidence of cross-platform testing.
If this sounds like your situation, the next step is a call.