A trait can now only be level up once within the same tier

module/data/actor/character.mjs

@@ -171,6 +171,13 @@ export default class DhCharacter extends BaseDataActor {
     }
 
     prepareBaseData() {
+        const currentLevel = this.levelData.level.current;
+        const currentTier =
+            currentLevel === 1
+                ? null
+                : Object.values(game.settings.get(SYSTEM.id, SYSTEM.SETTINGS.gameSettings.LevelTiers).tiers).find(
+                      tier => currentLevel >= tier.levels.start && currentLevel <= tier.levels.end
+                  ).tier;
         for (let levelKey in this.levelData.levelups) {
             const level = this.levelData.levelups[levelKey];
 
@@ -181,6 +188,7 @@ export default class DhCharacter extends BaseDataActor {
                     case 'trait':
                         selection.data.forEach(data => {
                             this.traits[data].bonus += 1;
+                            this.traits[data].tierMarked = selection.tier === currentTier;
                         });
                         break;
                     case 'hitPoint':

module/data/item/class.mjs

@@ -17,7 +17,6 @@ export default class DHClass extends BaseDataItem {
         return {
             ...super.defineSchema(),
             domains: new fields.ArrayField(new fields.StringField(), { max: 2 }),
-
             classItems: new fields.ArrayField(new ForeignDocumentUUIDField({ type: 'Item' })),
             evasion: new fields.NumberField({ initial: 0, integer: true }),
             features: new fields.ArrayField(new ForeignDocumentUUIDField({ type: 'Item' })),

module/data/levelup.mjs

@@ -1,3 +1,4 @@
+import { abilities } from '../config/actorConfig.mjs';
 import { chunkify } from '../helpers/utils.mjs';
 import { LevelOptionType } from './levelTier.mjs';
 
@@ -129,6 +130,35 @@ export class DhLevelup extends foundry.abstract.DataModel {
             .every(this.#levelFinished.bind(this));
     }
 
+    get unmarkedTraits() {
+        const possibleLevels = Object.values(this.tiers).reduce((acc, tier) => {
+            if (tier.belongingLevels.includes(this.currentLevel)) acc = tier.belongingLevels;
+            return acc;
+        }, []);
+
+        return Object.keys(this.levels)
+            .filter(key => possibleLevels.some(x => x === Number(key)))
+            .reduce(
+                (acc, levelKey) => {
+                    const level = this.levels[levelKey];
+                    Object.values(level.choices).forEach(choice =>
+                        Object.values(choice).forEach(checkbox => {
+                            if (
+                                checkbox.type === 'trait' &&
+                                checkbox.data.length > 0 &&
+                                Number(levelKey) !== this.currentLevel
+                            ) {
+                                checkbox.data.forEach(data => delete acc[data]);
+                            }
+                        })
+                    );
+
+                    return acc;
+                },
+                { ...abilities }
+            );
+    }
+
     get classUpgradeChoices() {
         let subclasses = [];
         let multiclass = null;