The Hex Editor I Built as a Hobby Became My Work

This spring, a Windows hex editor I had built as a hobby went viral.

A hex editor. Of all things.

I’m Yutaka Hirata, a Japanese programmer and writer living in Japan. When I speak Japanese, I have a Kansai accent. You probably won’t hear it in my English, but it’s there.

I’m in my fifties now, and I’m noticing more often that I don’t have the stamina I used to. Still here, though.

This summer was scorching again. Having the heat drain what energy you have is no small thing.

Recently, I visited Kanazawa Institute of Technology to check where I’d be taking an IT certification exam run by Japan’s Information-technology Promotion Agency. Seeing the young people on campus made me feel that perhaps I still had a few things left in me. It gave me a little energy.

Of course, feeling inspired doesn’t restore your physical stamina. Those are separate matters.

A hex editor displays the contents of a file in hexadecimal and lets you edit them directly. You use it to examine files that don’t make sense in an ordinary text editor, or to see how data is laid out. Familiar territory for programmers, perhaps, but hardly something everyone with a computer needs.

YuHex, the hex editor I built, displaying hexadecimal data alongside text containing Japanese characters and emoji.

Yet this rather unassuming tool attracted more attention than I expected. Even after years of writing software, you can’t predict these things.

I hadn’t identified a promising market, designed a product, and scored a hit exactly as planned. That would make a splendid story. Unfortunately, it isn’t mine. I made something, people noticed it, and only then did I start wondering what to do next.

How do you keep a hobby going?

When you write software as a hobby, you decide how to spend your time. Work on it when you feel like it. Find something else interesting, and spend your time on that instead. If you’re the only user, nobody is inconvenienced.

Once other people start using it, things change a little.

To the person who wrote it, it may be one program among many. To the person using it, it’s a tool they need. If it’s part of their daily work, “I got bored, so development is over” is going to be a problem.

I don’t think that means hobby developers owe everyone free maintenance forever. Software doesn’t eat, but the person making it does. Electricity costs money, too, and development time has to come from somewhere.

So I’m now developing this hex editor as a business. The point is to keep working on it.

People say turning a hobby into a job can make you hate something you once loved. It’s true that you can no longer do only the enjoyable parts. In my case, though, I decided to treat it as work because I wanted to continue. If I tried to fit everything into my spare time, other paid work would keep taking priority.

As a business, it gives me a reason to set aside time for development. It also means I need to bring in enough revenue to justify that time. In a way, I’m hiring myself to do the job. The client and the fellow struggling to implement the requests are the same middle-aged man.

A hex editor finds customers overseas

The software is called YuHex, and I distribute it through the Microsoft Store.

It’s quietly making sales.

“Went viral” may make it sound as though I’m earning enormous sums. Attention and paid purchases are different things. You can’t simply count everyone who talked about a program as a customer.

Still, people are paying for something I made. That feels good. They didn’t just take a look and move on. They chose it as a tool to install on their own computers and use.

There have been sales outside Japan as well. I’m grateful for that.

Somebody in another country is using my software. I understand how that works, of course, but seeing an actual sale still feels a little strange. Something I’m developing on the computer in front of me is being used across the sea.

Binary data is binary data, whether you look at it in Japan or somewhere else. 0A is 0A. FF is FF. Hexadecimal has no borders, I found myself thinking. Of course, you can’t write the user instructions entirely in hex, so that part needs separate attention.

Once there’s revenue, continuing development becomes more than a matter of enthusiasm. Spend time improving the software, then put those improvements into people’s hands. I don’t know where it will lead, but I’ve at least reached the point where I want to try continuing that way.

New tools, familiar questions

I use Visual Studio 2026—VS2026—to develop it. That’s the environment where I write the code, run it, and investigate what it’s doing.

For someone who has been programming for a long time, just seeing “2026” in the name of a development tool makes me feel we’ve come quite a way. My own age keeps increasing too, so perhaps I’m in no position to be surprised by numbers.

The tools change, but the questions involved in making software often don’t. What data are we handling? What counts as valid input? What happens when an unexpected value arrives? Building a screen and getting it to run feels good. What comes afterward takes rather longer.

For example, once you reach the end of a file, there’s no more data. But perhaps the interface looks as though you can select one more position. What should happen if someone presses a key there? These small questions aren’t really small.

A hex editor changes the contents of files. A display error is bad enough. Saving the wrong contents is worse. Before adding eye-catching features, I need to check that ordinary use produces ordinary, correct results. It sounds obvious when written down. Building up those obvious things, one by one, is much of what development involves.

I’ve worked on things such as the Linux kernel and embedded software—parts of computing that aren’t usually visible from the outside. A hex editor is another tool for looking at something normally hidden: the contents of a file. The subject changes, but perhaps I’ve always liked this sort of thing.

I look at rows of numbers on a screen and try to work out what’s in there. Even if I figure it out, someone unfamiliar with it might reasonably ask, “And?” But I find it interesting. As a reason to start a hobby, that was enough.

Now that I’m in my fifties, I sometimes wonder how long I’ll keep doing this. My stamina is declining, and I don’t expect determination to carry me through everything. Continuing exactly as I did when I was young is probably becoming unrealistic.

Still, I’d be sad to stop making new things. Software I made in the spring attracted attention, and now I’m developing it as a business. If I’d stopped simply because of my age, none of this would have happened.

Watching the young people at the university, I thought about all the things they might go on to make. I still have things I want to make, too.

For now, I want to keep this hex editor going, and do it properly.

Adapted from my Medium essay, originally written in Japanese for @IT Engineer Life.

AI tools assisted with the English translation and editing of my original Japanese essay. The experiences described are my own.