Inheriting a Legacy System Without Losing Your Mind

A surprising amount of custom software work isn't greenfield — it's taking over a system someone else wrote, often years ago, often without much documentation. Here's the process that keeps that from turning into a rewrite-everything death spiral.

Read before you touch

Before changing anything, we map what the system actually does versus what everyone assumes it does. Legacy systems accumulate small, undocumented business rules that look like bugs but are actually load-bearing.

Add tests around the parts you need to change

You don't need full test coverage on day one. You need enough coverage around the specific area you're about to modify that you'll know immediately if you broke something a customer depends on.

Resist the urge to rewrite everything

It's tempting to say "this would be so much cleaner if we just rebuilt it." Sometimes that's true. More often, a full rewrite trades a known set of bugs for an unknown set of new ones, on a system that was quietly working. We look for the smallest change that solves the actual business problem first.

When a rewrite really is the answer

Sometimes the underlying platform is the ceiling — it can't scale, can't integrate with what you need, or costs more to keep alive than to replace. In those cases we plan a phased migration rather than a big-bang cutover, so the business keeps running while the new system comes online.