Every American charity files one. Anyone can read it. Five lines answer most of what donors actually want to know.

The first time I tried to check whether a charity was any good, I did what most people do. I looked at a rating site, saw a number out of a hundred, and gave.
It took me two years of reading filings to understand that the number told me almost nothing, and that the document it was derived from told me a great deal. That document is the Form 990.
Total expenses, against line twelve, total revenue, over three years. You are not looking for a ratio. You are looking for whether the organisation is growing, shrinking, or spending down reserves.
A 990 will tell you what an organisation spent. It will not tell you whether the spending worked.
Read the filing before you give. It takes twenty minutes and it tells you more than any rating site will.