Every startup has a culture by around employee twenty. The only question is whether anyone chose it.
It isn't the perks
Snacks, offsites, a values page in the wiki — none of that is culture. Culture is what actually happens: who gets promoted, what behaviour gets walked past, how disagreement is handled, what happens when someone underperforms. People read the real signals, not the poster.
The worst behaviour a founder walks past becomes the floor.
Four things that set it
What you hire for. The behaviours in your scorecards are the behaviours you're choosing to multiply.
What you reward. The first few promotions tell everyone what this company actually values. If the person who hit their number by burning the team through gets promoted, that's now the deal.
What you tolerate. Everyone calibrates to the lowest bar you let stand.
How you communicate under pressure. In a crisis, the team copies the founder. Calm and straight, or sharp and shifting — it sets the tone for months.
Write it down, but keep it short
Three to five values, specific enough that you'd actually part ways with someone for breaking one. If they could belong to any company, they're not yours yet.
Where to start this week
Name the one behaviour you keep tolerating that you know you shouldn't. That gap — not the values page — is where your culture is really being decided.