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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

Updated: Enabling Drag and Drop between two Listboxes on a VBA Userform

I have updated the article about enabling drag and drop between two listboxes on an Excel userform with some improvements, including making the target box scroll up or down when there are more items than fit in the height of the listbox.

Tue, 11 Jan 2022 10:30:00 GMT

Office Script, more examples

I have added an example to my Office script examples page. Office Script does not (yet) offer a way to prompt for input. I invented a work-around: Check for a presence of an input sheet. If not there, Insert it into the file and populate it with a prompt and labelled input cells. If it is already there, assume all inputs are ready and continue running the script and perform its actions.

Mon, 13 Dec 2021 16:45:00 GMT

Updated : Flexfind

Flexfind has been updated: Now allows search in threaded comments.

Mon, 06 Dec 2021 14:35:00 GMT

Office Script, The basics updated

I've updated this article with the new feature to start a script from a button on a sheet.

Tue, 30 Nov 2021 10:55:00 GMT

Office Script, De basis is bijgewerkt

Ik heb dit artikel bijgewerkt met een nieuwe optie om een script te starten middels een knop op het werkblad

Tue, 30 Nov 2021 10:55:00 GMT

Updated: Compare Two Tables

I've updated the tool with some UI improvements.

Mon, 15 Nov 2021 10:15:00 GMT

Update: RefTreeAnalyser

RefTreeAnalyser 2.0 has just been updated to build 170. Improved sorting of chart series nodes on Objects dialog and fixed truncation of some labels on dialogs.

Wed, 10 Nov 2021 10:45:00 GMT

A tombola, built in Excel

Excel is a very serious and powerful business application. That doesn't mean we can't have some fun with it. This file shows how to use circular references to have a tombola, no programming involved!

Fri, 29 Oct 2021 13:45:00 GMT

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