Grabbed dndbeyond's source code

```
~/go/bin/sourcemapper -output ddb -jsurl https://media.dndbeyond.com/character-app/static/js/main.90aa78c5.js
```

ddb_main/packages/rules-engine/es/engine/RuleData/derivers.js

@@ -0,0 +1,51 @@
+import { getDamageAdjustments, getDiceValues, getLevelProficiencyBonuses, getStatModifiers, getStats, } from './accessors';
+/**
+ *
+ * @param ruleData
+ */
+export function deriveStatKeyLookup(ruleData) {
+    return getStats(ruleData).reduce((acc, stat) => {
+        acc[stat.id] = stat.key === null ? '' : stat.key.toLowerCase();
+        return acc;
+    }, {});
+}
+/**
+ *
+ * @param adjustmentType
+ * @param ruleData
+ */
+export function deriveDamageAdjustmentsByType(adjustmentType, ruleData) {
+    return getDamageAdjustments(ruleData).filter((adjustment) => adjustment.type === adjustmentType);
+}
+/**
+ *
+ * @param ruleData
+ */
+export function deriveLevelProficiencyBonusesLookup(ruleData) {
+    return getLevelProficiencyBonuses(ruleData).reduce((acc, item) => {
+        acc[item.level] = item.bonus;
+        return acc;
+    }, {});
+}
+/**
+ *
+ * @param ruleData
+ */
+export function deriveStatModifiersLookup(ruleData) {
+    return getStatModifiers(ruleData).reduce((acc, item) => {
+        acc[item.value] = item.modifier;
+        return acc;
+    }, {});
+}
+/**
+ *
+ * @param ruleData
+ */
+export function deriveVersatileDieLookup(ruleData) {
+    return getDiceValues(ruleData).reduce((acc, dieValue) => {
+        const diceValues = getDiceValues(ruleData);
+        const versatileIdx = Math.min(diceValues.length - 1, diceValues.indexOf(dieValue) + 1);
+        acc[dieValue] = diceValues[versatileIdx];
+        return acc;
+    }, {});
+}