Custom Code

Programs consist of text that people write and computers execute. This text is called code. Many companies buy ready-made programs, such as off-the-shelf accounting software. Custom code is the opposite: code that a company writes itself, or has written, specifically for its own operations. The comparison to clothing fits well. An off-the-rack suit is cheaper and available immediately, a tailor-made suit fits better and costs more.

Why companies still program things themselves

Standard software covers what many customers need. But it cannot capture what makes a single company special. A logistics company might have its own method for planning routes. That very method is its advantage over the competition. There is no product to buy for something like this, so it has to be programmed.

A second reason is connecting different systems. Almost every company uses several programs side by side that originally know nothing about each other. For data to flow between them, someone writes connecting pieces. These intermediate pieces are almost always custom code and are often invisible, but indispensable.

The price for this is ongoing. Ready-made software is maintained by the manufacturer, who closes security gaps themselves. A company’s own code must be maintained by itself for as long as it runs. Experts estimate that over the years, significantly more money flows into maintenance than into the initial development. Anyone who writes custom code is thus taking on a long-term commitment.

From wish to running program

At the beginning there is a requirement from the specialist department. Someone describes what the program should be able to do. Developers translate this description into code. In doing so, they mostly use ready-made building blocks, so-called libraries, that is, collections of already-solved standard tasks. Only the part that doesn’t exist anywhere yet is really written from scratch.

After that comes testing. Automated tests check after every change whether everything still works. Only then does the code go into real operation. This process repeats constantly, often several times a week. Software is never finished, it is merely left unchanged for a while.

For a few years now, AI tools have been getting involved. Assistants suggest entire sections of code while someone types. Studies show that a noticeable share of code at large companies is now generated by machines as a result. This shifts the work, but does not eliminate it. Someone still has to understand, review, and take responsibility for what ultimately runs.

Custom code in companies, apps, and headlines

You mainly encounter this term in the business world. When a bank announces it is modernizing its legacy systems, it is almost always about decades-old custom code. Such systems run reliably, but hardly anyone still fully understands them. The overhaul then costs hundreds of millions of euros and takes years.

The term also comes up with payment software. Providers of cloud services, meaning software that runs on the internet rather than on your own computer, often allow custom extensions. Customers write small add-on programs that are hooked into the purchased solution. That is custom code within a standard product.

A common misconception is equating custom code with bad code. The two have nothing to do with each other. In-house code only becomes problematic when nobody documents it and the original developers leave the company. It should also be distinguished from no-code tools, with which you click workflows together instead of programming them. These are faster, but quickly hit their limits.