diff --git a/app/imports/api/properties/RollModifier.js b/app/imports/api/properties/RollModifier.js
new file mode 100644
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--- /dev/null
+++ b/app/imports/api/properties/RollModifier.js
@@ -0,0 +1,52 @@
+import SimpleSchema from 'simpl-schema';
+
+/*
+ * RollModifiers are reason-value attached to rolls
+ * that modify their final value in some way
+ * These are separate from effects because they are a always a result of the
+ * creature's stats, and never cause a recomputation themselves
+ */
+let RollModifierSchema = new SimpleSchema({
+	name: {
+		type: String,
+		optional: true,
+	},
+	operation: {
+		type: String,
+		defaultValue: 'add',
+		allowedValues: [
+			'damageBonus',
+      'rollBonus',
+		],
+	},
+	calculation: {
+		type: String,
+		optional: true,
+	},
+	// which tags the modifier is applied to
+  // all tags must match
+	'tags.$': {
+		type: String,
+		optional: true,
+	},
+});
+
+const StoredRollModifierSchema = new SimpleSchema({
+		_id: {
+			type: String,
+			regEx: SimpleSchema.RegEx.Id,
+			autoValue(){
+				if (!this.isSet) return Random.id();
+			}
+		},
+}).extend(RollModifierSchema);
+
+const ComputedRollModifierSchema = new SimpleSchema({
+	// The computed result of the effect
+	result: {
+		type: SimpleSchema.oneOf(Number, String),
+		optional: true,
+	},
+}).extend(RollModifierSchema);
+
+export { RollModifierSchema, StoredRollModifierSchema, ComputedRollModifierSchema };