diff --git a/lib/utils/mutate.js b/lib/utils/mutate.js
new file mode 100644
index 0000000..3dc3f52
--- /dev/null
+++ b/lib/utils/mutate.js
@@ -0,0 +1,52 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+utils.mutate = {
+  text: function (str) {
+    let mutator = function (m) {
+      return random.number(4) === 1 ? m : make.text.any()
+    }
+    return str.replace(/[a-zA-Z]+?/g, mutator)
+  },
+
+  numbers: function (str) {
+    let mutator = function (m) {
+      return random.number(4) === 1 ? m : make.number.any()
+    }
+    return str.replace(/-?\d+(\.\d+)?/g, mutator)
+  },
+
+  units: function (str) {
+    let mutator = function (m) {
+      return random.number(4) === 1 ? m : make.unit.unit()
+    }
+    return str.replace(/(px|em|ex|ch|rem|mm|cm|in|pt|pc|%')/g, mutator)
+  },
+
+  random: function (str) {
+    let mutator = function (m) {
+      if (random.number(20) === 1) {
+        if (str.match(/[0-9]/g)) {
+          return make.number.any()
+        } else {
+          return make.text.any()
+        }
+      } else {
+        return m
+      }
+    }
+    return str.replace(/./g, mutator)
+  },
+
+  any: function (str) {
+    switch (random.number(3)) {
+      case 0:
+        return utils.mutate.text(str)
+      case 1:
+        return utils.mutate.numbers(str)
+      case 2:
+        return utils.mutate.units(str)
+    }
+  }
+}