Why I Built String GOAT: How a Tennis Player's Frustration Became an App

I picked up my first tennis racket in 1999. Over 20 years of playing, I've restrung my rackets countless times — but I could barely remember which string I used at what tension, or how it actually felt during a match. That frustration became String GOAT — a tennis string tracking app with feedback analysis and AI-powered recommendations.

Depending on the Stringer

I always left stringing to the shop. Whatever the stringer recommended, I went with it. But at some point, something felt wrong.

I was the one playing with those strings, yet I was depending entirely on someone else to make the choice. The irony? That stringer had never once watched me play with the setup they prepared.

My racket, my play style, my performance — only I could know how a string actually felt on court. But none of that data was being recorded anywhere.

The Spreadsheet Limitation

So I started logging everything in Google Sheets. String brand, model, tension, and detailed feedback — control, power, spin, comfort, feel, durability — six dimensions for every restring.

The actual spreadsheet I used. As data grew, it became harder to manage.

But as the data grew, the problems became clear.

• Mobile input was painful. Right after a match, when the feeling was fresh, I wanted to log it instantly. Spreadsheets weren't built for that.
• No data visualization. Dozens of records piled up, but I still couldn't answer: "So what's the best string for me?"
• Patterns were invisible. The correlation between tension and spin, seasonal tension changes — insights buried in rows and columns.

Why Existing Solutions Didn't Work

String management software does exist — but it's built for stringing shops. B2B tools designed for customer management and job tracking, not for the player who actually plays with those strings.

There was nothing for recreational players like me.

The Stringing Machine and My Wife's Words

Having studied Sports Science in university, I understood that the impact of strings and tension on performance wasn't just a gut feeling — it was something that could be systematically analyzed. But the data needed for that analysis simply didn't exist.

As tennis grew more popular in Korea, shop wait times got longer and restringing costs went up. So I decided to buy a stringing machine.

The math was simple: string my racket and my wife's a few times, and the machine pays for itself. After that, it's basically free money. Spoiler: my math was wrong.

But buying the machine sparked something bigger. Combined with my frustration over spreadsheets, I wanted to build something better.

When I told my wife I wanted to build an app, she said one thing:

"Then build it!"

Without that moment, String GOAT would never have existed.

String GOAT Was Born

I started building it purely for myself. An app to quickly log strings, leave feedback, and let AI analyze the data to recommend the best string and tension for my game.

The core problems String GOAT solves are simple:

• Log in 30 seconds. Right on court, right after a match, from your phone
• Feedback system. Rate control, power, spin, comfort, feel, and durability
• AI analysis. The more data you log, the smarter the recommendations get
• Cloud sync. Same data on the app and web dashboard, anywhere
• Import your data. Already have records in Excel or Google Sheets? AI auto-detects and imports them. No need to start from scratch

178 Countries, 15,000+ Downloads

I never expected an app I built for myself to be downloaded over 15,000 times across 178 countries.

What I discovered along the way: tennis players around the world love experimenting with the endless combinations of strings. It's a hobby within a hobby. Beyond just playing the game, there's a passion for constantly optimizing their racket setup.

String GOAT adds data and AI to that passion.

Now and Beyond

Today, String GOAT is available on iOS, Android, and a web dashboard. It supports 13 languages, and AI analyzes your records to recommend optimal strings and tension.

The String GOAT web dashboard. Manage the same data on a bigger screen.

I still think about it every day — how can I help self-stringers and tennis players around the world even more? Each answer gets built into the service, one update at a time.

Still tracking your strings in a spreadsheet?

Start free on iOS or Android. You can also check the web dashboard.

Want to understand the science behind when poly strings go dead? Read the dead string science guide →