Requires the library mod Collective.

Enchantment Level Cap Indicator is a client-side mod that helps players determine whether an enchantment on an item is maxed out. While more experienced players have each level cap memorized, new adventurers do not. A symbol is placed next to the enchantment level when it has reached its maximum potential. By default a golden star is used, though you can change this to whatever you prefer in the config.

Works in the enchantment table, anvil and inventory item tool tips.

Configurable: ( how do I configure? )
maxLevelSymbol (default = "⭐"): The symbol used to show that an enchantment is the maximum level. By default a star.
maxLevelSymbolColourIndex (default = 6, min 0, max 15): The colour index value used for the max level symbol. Possible values; 0: black, 1: dark_blue, 2: dark_green, 3: dark_aqua, 4: dark_red, 5: dark_purple, 6: gold, 7: gray, 8: dark_gray, 9: blue, 10: green, 11: aqua, 12: red, 13: light_purple, 14: yellow, 15: white

Easily see what enchantments are maxed on your tools!

Here's a GIF showing the full mod functionality:

Shows the symbol next to the enchantment clue:

Works in the anvil as well:

Don't like the star? Use your own custom symbol and colour!

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You may freely use this mod in any modpack, as long as the download remains hosted within the CurseForge ecosystem.

Serilum.com contains an overview and more information on all mods available.

Comments are disabled as I'm unable to keep track of all the separate pages on each mod.
For issues, ideas, suggestions or anything else there is the Github repo. Thanks!