diff --git a/app/assets/javascripts/workers/aether_worker.js b/app/assets/javascripts/workers/aether_worker.js
index 560b70c4e..810537599 100644
--- a/app/assets/javascripts/workers/aether_worker.js
+++ b/app/assets/javascripts/workers/aether_worker.js
@@ -1,7 +1,7 @@
 var window = self;
 var Global = self;
 
-importScripts("/javascripts/lodash.js", "/javascripts/aether.js");
+importScripts("/javascripts/lodash.js", "/javascripts/aether.js", "/javascripts/esper.js");
 //console.log("Aether Tome worker has finished importing scripts.");
 var aethers = {};
 var languagesImported = {};
diff --git a/app/assets/javascripts/workers/worker_world.js b/app/assets/javascripts/workers/worker_world.js
index 65ba1b42e..7d03e647e 100644
--- a/app/assets/javascripts/workers/worker_world.js
+++ b/app/assets/javascripts/workers/worker_world.js
@@ -63,7 +63,7 @@ var console = {
 console.error = console.warn = console.info = console.debug = console.log;
 self.console = console;
 
-self.importScripts('/javascripts/lodash.js', '/javascripts/world.js', '/javascripts/aether.js');
+self.importScripts('/javascripts/lodash.js', '/javascripts/world.js', '/javascripts/aether.js', '/javascripts/esper.js');
 var myImportScripts = importScripts;
 
 var languagesImported = {};
diff --git a/app/assets/main.html b/app/assets/main.html
index 6c38316e0..717b8985b 100644
--- a/app/assets/main.html
+++ b/app/assets/main.html
@@ -61,6 +61,7 @@
   <script src="/javascripts/box2d.js"></script>
   <script src="/javascripts/vendor.js"></script>
   <script src="/javascripts/aether.js"></script>
+  <script src="/javascripts/esper.js"></script>
   <script src="/javascripts/app.js"></script>
   <![endif]-->
   <!-- IE9 cors support breaks analytics logging: http://caniuse.com/#feat=cors -->
@@ -71,6 +72,7 @@
   <script src="/lib/ace/ace.js" defer></script>
   <script src="/javascripts/vendor.js" defer></script>
   <script src="/javascripts/aether.js" defer></script>
+  <script src="/javascripts/esper.js" defer></script>
   <script src="/javascripts/app.js" defer></script>
   <![endif]>
   <script>
diff --git a/app/lib/aether_utils.coffee b/app/lib/aether_utils.coffee
index 258f1b15a..63c99dd58 100644
--- a/app/lib/aether_utils.coffee
+++ b/app/lib/aether_utils.coffee
@@ -1,3 +1,5 @@
+utils = require 'core/utils'
+
 Aether.addGlobal 'Vector', require './world/vector'
 Aether.addGlobal '_', _
 
@@ -27,6 +29,7 @@ module.exports.createAetherOptions = (options) ->
     #functionParameters: # TODOOOOO
     executionLimit: 3 * 1000 * 1000
     language: options.codeLanguage
+    useInterpreter: !!utils.getQueryVariable('esper') 
   parameters = functionParameters[options.functionName]
   unless parameters
     console.warn "Unknown method #{options.functionName}: please add function parameters to lib/aether_utils.coffee."
diff --git a/bower.json b/bower.json
index 3bc0a2f44..f21566e2c 100644
--- a/bower.json
+++ b/bower.json
@@ -32,7 +32,7 @@
     "firepad": "~0.1.2",
     "marked": "~0.3.0",
     "moment": "~2.5.0",
-    "aether": "~0.4.0",
+    "aether": "~0.4.5",
     "underscore.string": "~2.3.3",
     "firebase": "~1.0.2",
     "d3": "~3.4.4",
@@ -48,7 +48,8 @@
     "backfire": "~0.3.0",
     "fastclick": "~1.0.3",
     "three.js": "~0.71.0",
-    "lscache": "~1.0.5"
+    "lscache": "~1.0.5",
+    "esper.js": "http://files.codecombat.com/esper.tar.gz"
   },
   "overrides": {
     "backbone": {
diff --git a/config.coffee b/config.coffee
index 3085e53d9..73af9e603 100644
--- a/config.coffee
+++ b/config.coffee
@@ -93,12 +93,12 @@ exports.config =
         #- vendor.js, all the vendor libraries
         'javascripts/vendor.js': [
           regJoin('^vendor/scripts/(?!(Box2d|coffeescript|difflib|diffview|jasmine))')
-          regJoin('^bower_components/(?!(aether|d3|treema|three.js))')
+          regJoin('^bower_components/(?!(aether|d3|treema|three.js|esper.js))')
           'bower_components/treema/treema-utils.js'
         ]
         'javascripts/whole-vendor.js': if TRAVIS then [
           regJoin('^vendor/scripts/(?!(Box2d|jasmine))')
-          regJoin('^bower_components/(?!aether)')
+          regJoin('^bower_components/(?!aether|esper.js)')
         ] else []
 
         #- Other vendor libraries in separate bunches
@@ -109,6 +109,7 @@ exports.config =
         'javascripts/box2d.js': regJoin('^vendor/scripts/Box2dWeb-2.1.a.3')
         'javascripts/lodash.js': regJoin('^bower_components/lodash/dist/lodash.js')
         'javascripts/aether.js': regJoin('^bower_components/aether/build/aether.js')
+        'javascripts/esper.js': 'bower_components/esper.js/esper.js'
         'javascripts/app/vendor/aether-clojure.js': 'bower_components/aether/build/clojure.js'
         'javascripts/app/vendor/aether-coffeescript.js': 'bower_components/aether/build/coffeescript.js'
         'javascripts/app/vendor/aether-io.js': 'bower_components/aether/build/io.js'
@@ -158,6 +159,7 @@ exports.config =
           'bower_components/tv4/tv4.js'
           # Aether before box2d for some strange Object.defineProperty thing
           'bower_components/aether/build/aether.js'
+          'bower_components/esper.js/esper.js'
           'bower_components/fastclick/lib/fastclick.js'
           'bower_components/d3/d3.min.js'
           'vendor/scripts/async.js'
diff --git a/package.json b/package.json
index 8d8c4c5b7..c5a0c4377 100644
--- a/package.json
+++ b/package.json
@@ -52,7 +52,7 @@
   "dependencies": {
     "JQDeferred": "~2.1.0",
     "ace-builds": "https://github.com/ajaxorg/ace-builds/archive/3fb55e8e374ab02ce47c1ae55ffb60a1835f3055.tar.gz",
-    "aether": "~0.4.0",
+    "aether": "~0.4.5",
     "async": "0.2.x",
     "aws-sdk": "~2.0.0",
     "bayesian-battle": "0.0.7",