We built a founder's spreadsheet into a product its owner can trust.

Leave Dates began as a free Excel planner downloaded more than 10,000 times. OneSyntax helped turn that validated idea into a staff holiday product now used by thousands of customers — and has kept the same codebase healthy since the first commit in 2018.

Case Study 2 min read

Most products start as a workaround. For Leave Dates, it was a spreadsheet: a free Excel holiday planner that small businesses downloaded more than 10,000 times. That is about as strong a signal as an idea can get before it becomes software. People were already using it, and they were already running into its limits.

The question was not whether to build a product. It was how to build one that kept what people liked about the spreadsheet — it was simple, and it was theirs — while removing everything that made it fragile.

Keep the simple thing simple

A leave planner has a clear job: show who is away, let people ask for time off, and let someone approve it. Everything we added had to make that job easier, not bigger. New rules, teams and integrations arrived over the years, but the first screen still answers the first question: who is off, and when?

That meant saying no to some features and putting others behind sensible defaults. The product grew; the everyday experience did not.

The same team since the first commit: 8 years
Automated tests on every change: ~4,500
Major framework upgrades, never rewritten: 9

Earn trust one release at a time

A founder who has built something by hand is right to be careful about handing it over. Trust came from small, visible steps: working software every week, plain-English acceptance scenarios the business could read, and a test suite that runs before anything reaches a customer.

Over time those habits became the product's safety net. Today there are around 4,500 automated tests and more than 1,000 acceptance scenarios, so a change to one corner of the product does not quietly break another.

Never rewrite, keep upgrading

The same codebase has carried Leave Dates since 2018, through nine major framework upgrades. Keeping a product current in small steps is less exciting than a rewrite, and far less risky: customers never had to wait for a "new version" to get the next improvement.