When you need this

The system your site has to talk to is old, or specific to your trade. Warehouse software. An accounting package with one way in, documented years ago. A supplier’s price file that arrives every week with the columns in a slightly different order.

The last developer who looked at it said it cannot be done, or quoted for replacing the whole thing. Usually neither is true.

What I actually build

A look inside first, as a small job with its own fixed price. Pricing an unexplored old system blind is how both sides end up unhappy; once I know what it can do, the build gets its own fixed price in writing.
One small piece of code that knows the other system’s quirks; the rest of your site talks to it in plain terms. When that system is finally replaced, one piece is replaced and nothing else.
Bad data caught at the door. A file from a system nobody maintains will one day arrive broken, half-sent, or with the accents turned into question marks. It stops there with a message to you, not in your catalogue.
What happens if the other side changes without warning, agreed in writing — because sooner or later it will.

Where this shows up in my work

None of the published cases is a connection to an old system. The nearest is A rental fleet with four contracts and one booking flow: no booking plugin fitted twelve-month hire, so I wrote the missing piece instead of bending a plugin — the same approach, applied to a system nobody has a plugin for.

What you get

A working connection, one replaceable piece between your site and the old system, and a written account of what that system actually does. Priced above a standard connection because the unknowns are harder, not the code — and saying so up front is what keeps the project from quietly overrunning.