Roughly speaking, organisations that rate/assess charities fall into two categories:

Those that include thoughtful, impact-oriented, cost-effectiveness-aware analysis tend not to use a formulaic or index-based or scalable approach. Examples of this sort of organisation include GiveWell. I created this chart some time back, since then Founders Pledge could probably added to this category.

In the opposite corner is those organisations whose methodology is more formulaic/scalable.

At the time I created this chart, there was a gap for analysis that was scalable, but also impact-oriented and cost-effectiveness-aware.

Since then I've set up SoGive to resolve this gap. You can have a look on https://app.sogive.org/ and search for charities or cause areas there. Some charities are assessed as Gold, Silver, or Bronze. We are still working through the charities, so not all of them have a rating. If you click through to a charity's page, you'll see a tab called analysis. Lots (but not all) major UK charities are covered her. In the US the closest organisation to SoGive (in terms of approach) is Impact Matters.