Introduction

In this article I’ll show you how to create a UDF library for Excel in C# from scratch.
By “from scratch” I mean without using Visual Studio, only low-level tools : a simple text-editor like Notepad and the C# compiler.
This is of course not the way you’ll do it usually but it will hopefully help you to better understand how things work under the hood.

The pretext for this sample is a set of functions that provides financial data like the last bid and ask prices for a stock.
It uses the Yahoo finance REST API which is rich and simple and that you could use as a base for developing more advanced tools.
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