Some of the most important software a business runs on is also the most closed. It has no public API, or the vendor will sell you one at a price that only makes sense if you are a much larger company. Either way, the data you need is trapped inside a system you do not control.
The usual answer is to have a person re-key that data by hand, forever. I do not accept that answer. If a system will not hand me an API, I build one in front of it.
Read what it already emits
Almost every legacy system already talks. It sends confirmation emails, writes export files, or drops reports on a schedule. That output is a data source. I run a lightweight service beside the old system, set up an inbound address or a watched folder, and parse whatever arrives. Order numbers, tracking IDs, status changes, all of it becomes structured data.
From there it flows through a clean API into the modern system your team actually uses, and the customer gets notified automatically. The legacy codebase is never touched, and nobody had to pay a toll for access.
Where the care goes
Parsing someone else’s output is brittle by nature. Formats drift, a template changes, an edge case shows up that you did not plan for. So the bridge is only as good as its testing and its alerting. I validate every field, log every message, and fail loudly when something does not match, instead of silently passing bad data downstream. Done that way, a closed system becomes a dependable, connected part of the stack.