As Donald Trump was fighting with Congress over the shutdown and funding for a border wall, his administration implemented a new rule that could be a game-changer for health care.

Starting this month, hospitals must publicly reveal the contents of their master price lists — called “chargemasters” — online. These are the prices that most patients never notice because their insurers negotiate them down or they appear buried as line items on hospital bills. What has long been shrouded in darkness is now being thrown into the light.

For the moment, these lists won’t seem very useful to the average patient — and they have been criticized for that reason. They are often hundreds of pages long, filled with medical codes and abbreviations. Each document is an overwhelming compendium listing a rack rate for every little item a hospital dispenses and every service it performs: A blood test for anemia. The price of lying in the operating suite and recovery room (billed in 15-minute intervals). The scalpel. The drill bit. The bag of IV salt water. The Tylenol pill. No item is too small to be bar coded and charged.

But don’t dismiss the lists as useless. Think of them as raw material to be mined for billing transparency and patient rights. For years, these prices have been a tightly guarded industrial secret. When advocates have tried to wrest them free, hospitals have argued that they are proprietary information. And, hospitals claim, these rates are irrelevant, since — after insurers whittle them down — no one actually pays them.