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Welcome to the website of JKP Application Development Services

What I do


I offer services pertaining to any aspect of Excel and VBA. My Services page shows you examples of services I provide. You will also find a list of recent projects there.


I develop bespoke Excel tools for customers and also Excel add-ins for the general public, like my spreadsheet auditing tool RefTreeAnalyser. Check out products I have developed.


I offer both pre-scheduled trainings and custom-made courses. Content of trainings can be adapted to your needs. If preferred we also offer any course as an in-house training.


Subscribe to our news letter or check out the archive. There is no set frequency, I just post something when I have time. In any case, it is all about Excel.

Free Excel tools

I develop custom-made applications using Microsoft Office Excel® and VBA and Access and VBA to their full extent. Have a look at various (free) downloads, some of which have become the de facto standard for Excel developers around the world.

Who is Jan Karel?

Would you like to learn more About me? On this page you can get to know me a little better and also find a short list of presentations I've given over the past years.

What's new on this site

English and/or Dutch content

Getting rid of the "cannot find your add-in" message
Many users struggle with getting rid of an Excel add-in. In this article I show how to fix the infamous "Sorry, we could not find..." error message.
Wed, 14 Jul 2021 14:45:00 GMT

A self-installing add-in
Many users struggle with getting an add-in installed. In this article I show some VBA code that will ease that process: As soon as the user opens the add-in and enables macros, the add-in offers to install itself.
Mon, 12 Jul 2021 13:40:00 GMT

Office Script, de basis
Sinds 2020 kunnen Microsoft 365 gebruikers hun acties in Excel online opnemen tot Office Script macro's. Dit artikel laat zien hoe je daarmee begint. Later zal ik nog wat voorbeeld scripts plaatsen die niet kunnen worden opgenomen, maar wel handig kunnen zijn.
Thu, 08 Jul 2021 13:45:00 GMT

Excel LAMBDA functie, de basis
Een artikel over de nieuwe Excel LAMBDA functie: hoe maak ik mijn eigen Excel functies.
Tue, 06 Jul 2021 12:40:00 GMT

Office Script, the basics
Since 2020, Microsoft 365 users can record their actions in Excel on-line into Office Script macros. This article shows you how to get started. Later on, I will list some example scripts which you cannot record but might come in handy.
Mon, 05 Jul 2021 16:00:00 GMT

Excel LAMBDA function, converting VBA UDFs to Lambda functions
The new Excel LAMBDA function: how to convert well-known VBA structures into combinations of Excel functions in a Lambda.
Tue, 08 Jun 2021 16:50:00 GMT

Excel LAMBDA function, the basics
An article about the new Excel LAMBDA function: how to create your own Excel functions.
Wed, 02 Jun 2021 14:15:00 GMT

Updated various tools
I have updated GitHubVBAExporter, the form is now sizable.
Wed, 28 Apr 2021 11:00:00 GMT

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