Why ship behind a flag?

A feature flag is a switch in your code. The new feature ships off by default. You flip it on for a slice of users, watch what happens, then expand — or roll back in seconds if something breaks. No re-deploy, no panic.

Most teams build flags themselves, badly, three times before they admit they need a real one. Here are the four moments when the cost-of-not-having-a-flag shows up.

1. The risky release

You're shipping a checkout rewrite. It works on staging. It worked in code review. It will probably work in production. "Probably" is the word that costs you weekends. Ship it behind a flag, flip it on for 5%, watch your conversion rate for an hour. If it holds, expand. If it doesn't, you flip it back in the time it takes to refresh a dashboard.

2. The A/B test you keep meaning to run

Sheepit experiments are flags with two variants and a metric attached. Same code path, same SDK, same audit log. You don't need a second tool, a third dashboard, or a stats consultant — just pick a flag, pick a goal, split traffic, wait for significance.

3. The paid feature

Pro-tier features are the same switch, gated by a different rule. Free users get false. Pro users get true. Trial users get true for 14 days. Internal users get true forever. All of that is one flag and a handful of rules.

4. The beta group

You're showing the new dashboard to your three friendliest customers before everyone else sees it. Create a cohort ("emails ending in @acme.com"), attach the flag, done. When you're ready to expand, you change the rule — not the code.