Engineering / Going TypeScript end to end

2.6K WORDS · KOHTA KOUCHI

Going TypeScript end to end

Why I standardise the whole codebase on types — and what it actually buys a small team.

FIG · 1 · 2026.02

Types aren't about catching typos. The real win is that they turn a refactor from an act of courage into a chore the compiler walks you through. On a small team that difference is the difference between shipping and stalling.

When I standardised Simple's codebase on TypeScript during the migration, the payoff wasn't fewer bugs in week one — it was that six months later a new contributor could rename a field and trust the red squiggles to find every caller.

The cost is real: stricter code is slower to write the first time. I pay it anyway, because most code is read and changed far more than it's written.