The free key's 100 requests a day sounds like a constraint until you run the arithmetic the other way: one request returns a whole sport board. Reading every sport you care about, live and prematch, costs a few dozen calls. An afternoon on the free key is enough to evaluate the entire shape of the feed before you spend anything.
The budget you are working with
The free tier is REST access to live and prematch markets with the full line depth, limited to 20 requests a minute and 100 a day, with no card and no expiry, as the free key page states, checked 2026-10-02. The key reaches the same endpoints and returns the same envelope as the paid plans, so everything you learn about the data carries over; only the rate changes later.
One request, one sport board
Each markets call takes a sport ID and returns every event on that board with its lines. There is no pagination marathon and no per-league fee: the evaluation plan is a short loop over the sport IDs you care about. A single busy soccer board can hold hundreds of events, which is why the per-day count goes further than it looks.
Two practical notes from the coverage page: the documented sport list, not any headline count, is the list to work from, because the published sport counts disagree; and prematch boards have their own documented route, so check both shapes against what your application needs.
What to look at in each response
Read the envelope before the prices: an events array plus the last cursor you would send back as since. Inside an event, the markets sit under period keys, and the full-match market is period 0. Confirm your parser finds the money line, the spreads and the totals where you expect them, and keep one raw response for debugging later.
This is also the moment to test your error handling: send a bad key once and read the 401, so the real errors never surprise you.
What an afternoon cannot tell you
Three things stay unevaluated. The SSE stream and the raw WebSocket are not on the free key; the three-day demo exists for those, on request. A 20-a-minute ceiling cannot show you how your loop behaves at 10 requests a second. And one afternoon is one slice of time: it proves the shape of the data, not its rhythm across a busy week.
Budget an hour for the boards, an hour for the parser, and keep the rest of the 100 calls for the questions that appear while you work. That is the whole evaluation, and it costs nothing but the afternoon.