I often use F3 to look at entity data, sometimes block data too. I often even /data get @e[...] to see more detailed data of an entity. Being able to see these as a info toggles would be a great feature.

Choosing to see info details on the right hand side of the screen would also help a lot, so you can customize the output. Currently we have a boolean true/false to show or hide it. I suggest changing this to false/left/right.

There are already some basic things that you can view as info lines, such as the entity registry name and the health of living entities, and the block registry name and block state properties. I will probably add more things such as the block tags that are on the F3 screen, and probably the entity or block entity NBT data as well.

And I'm also thinking I will probably add additional configurable info line "groups", so that you can create more info line groups and select a number of info lines for each group, and then select the location of the group (top left, top right, bottom left etc.) And fully customizable info line formats are also planned (and partially implemented in a dev branch). Unfortunately I'm very badly backlogged, and new features are still added in 1.12.2 first, so the ETA for all of these to end up in the latest (such as 1.15.2 or 1.16.1) versions is totally unknown, and not any time soon.

I'm looking through the code, and I can't for the life of me figure out which class is the one adding info to the panel, nor which class is the actual renderer of the infopanel. I'll gladly help out if I learn how the mod works.

There are already some basic things that you can view as info lines, such as the entity registry name and the health of living entities, and the block registry name and block state properties. I will probably add more things such as the block tags that are on the F3 screen, and probably the entity or block entity NBT data as well.

And I'm also thinking I will probably add additional configurable info line "groups", so that you can create more info line groups and select a number of info lines for each group, and then select the location of the group (top left, top right, bottom left etc.) And fully customizable info line formats are also planned (and partially implemented in a dev branch). Unfortunately I'm very badly backlogged, and new features are still added in 1.12.2 first, so the ETA for all of these to end up in the latest (such as 1.15.2 or 1.16.1) versions is totally unknown, and not any time soon.

Isn't the data we now have access to accessed through the NBT data? Being able to customize a query to the NBT data of the selected block/entity might make it easier for both development and usage.

There is currently nothing based on NBT data in the info lines. All the data comes from various different sources (method calls on entities/blocks/the world object etc.). Well actually I think the bee hive info line is based on the bee hive block entity NBT data, but that's currently the only thing.

All the info lines are generated here:

And yes, that stuff needs clean-up and a rewrite. And the customizable info lines stuff will basically get rid of all of this old code.

Or you can use the ClientCommands /cgetdata for more NBT stuff