Can you take over something another developer built?

Yes, and it comes up more than anyone in this industry admits publicly.

The call usually starts apologetically, as if it reflects badly on the client. It rarely does.

What I check first

• Do you have the code? Not "does it exist" — do you have it, in a repository in your name. If the answer is that the developer has it, that is the first problem to solve, and it is a commercial problem, not a technical one.
• Are the infrastructure accounts yours? Hosting, domain, database. If they are in the developer's name, sort this before anything else.
• Is anything documented? Usually not. This is survivable, just slower.
• Is it running? Something live and imperfect is a much better starting point than something half-finished.

The honest bit

Sometimes the right answer is to rebuild rather than inherit. I do not say that lightly, because it sounds exactly like what a new supplier would say to increase their fee.

So I will show you the reasoning: how long it takes to understand what exists, versus how long to rebuild the parts you actually use. Frequently the answer is inherit the working parts and rebuild one area.

What I will not do

I will not run down the previous developer. Some of these projects went wrong for reasons that were not the developer's fault at all — scope that moved, a client who could not give time, a spec nobody pinned down. I have been on the other side of that.

What I will do is tell you plainly what state it is in.