The in-network file is the largest and most useful MRF. For each covered item or service, identified by a billing code, it lists the negotiated rates and which providers each rate applies to.
Rates carry details that matter for comparison: whether the rate is professional or institutional, the place of service it applies to, any billing code modifiers, and the type of rate, such as a fixed negotiated dollar amount, a percentage, or a per diem.
Providers are referenced by NPI and TIN, often through shared provider reference lists so the same group of providers isn't repeated for every rate.