Would it be possible to have certain rules and height restrictions of displayed in JEI via JER? Right now JER can show which biomes and what which light levels a mob can spawn (sometimes it is not accurate though), but I plan to heavily customize spawn rules for certain mobs and wanted a concise way to deliver this information to the end-user (such as JEI).

Not sure how you would represent these json rules in a player friendly manner?

So using this as an example: https://imgur.com/a/B9RVB

There is still some whitespace for about 5-6 lines of text, possibly more if the image of the blaze and its loot table is shifted down lower. As long as the rule isn't modified or doesn't show up in the JSON, it won't appear in JER- but if there is something new modifying endermen spawn height it will show up. ]

Formatting could be alphabetical order and only the following rules only need to be communicated to players in my opinion.

Blaze

Block: {string}
Dimension: {dimensionID}
Height: {minheight} - {maxheight}
Light Level: {minlight} - {maxlight}
Time: {mintime} - {maxtime}
Needs Sky: {boolean}
Weather: {string}

I do not think it would be possible to represent more complicated rules, like endermen spawning in the End above a certain Y level will have more health or deal more damage, but the basic rules regarding where a mob can spawn should be communicated (only if the behavior is altered). Another problem I see is a modpack maker inputing an extremely large list of blocks for the block spawn, which could clutter up the entire JEI screen, but that only seems to be a corner case.

@McJty I would also be interested. Precisely because it is completely wrong information:

[
  {
    "mob": "mysticalworld:frog",
    "removeall": true
  },
  {
    "mob": "mysticalworld:frog",
    "item": "quark:frog_leg",
    "itemcount": "1"
  }
]