diff --git a/doc/usage.md b/doc/usage.md
index f9daf47ff2..46baecce82 100644
--- a/doc/usage.md
+++ b/doc/usage.md
@@ -95,6 +95,15 @@ to5.transformFile("filename.js", options, function (err, result) {
 });
 ```
 
+### to5.transform.fromAst(ast, [code], [opts])
+
+```javascript
+var result = to5.transform(ast, "var a = 2;", opts);
+result.code;
+result.map;
+result.ast;
+```
+
 #### Options
 
 ```javascript
diff --git a/lib/6to5/file.js b/lib/6to5/file.js
index de9957fe79..0e1207b023 100644
--- a/lib/6to5/file.js
+++ b/lib/6to5/file.js
@@ -156,14 +156,16 @@ File.prototype.errorWithNode = function (node, msg, Error) {
   return err;
 };
 
-File.prototype.parse = function (code) {
+File.prototype.addCode = function (code) {
   code = (code || "") + "";
+  this.code = code;
+  return this.parseShebang(code);
+};
 
+File.prototype.parse = function (code) {
   var self = this;
 
-  this.code = code;
-
-  code = this.parseShebang(code);
+  this.addCode(code);
 
   return util.parse(this.opts, code, function (tree) {
     self.transform(tree);
diff --git a/lib/6to5/transformation/transform.js b/lib/6to5/transformation/transform.js
index 497d65d376..94afc696c4 100644
--- a/lib/6to5/transformation/transform.js
+++ b/lib/6to5/transformation/transform.js
@@ -2,6 +2,7 @@ module.exports = transform;
 
 var Transformer = require("./transformer");
 var File        = require("../file");
+var util        = require("../util");
 var _           = require("lodash");
 
 function transform(code, opts) {
@@ -9,6 +10,15 @@ function transform(code, opts) {
   return file.parse(code);
 }
 
+transform.fromAst = function (ast, code, opts) {
+  ast = util.normaliseAst(ast);
+
+  var file = new File(opts);
+  file.addCode(code);
+  file.transform();
+  return file.generate();
+};
+
 transform._ensureTransformerNames = function (type, keys) {
   _.each(keys, function (key) {
     if (!_.has(transform.transformers, key)) {
@@ -30,9 +40,9 @@ transform.moduleFormatters = {
 
 _.each({
   // spec
-  _blockHoistFunctions:      require("./transformers/spec-block-hoist-functions"),
-  _noForInOfAssignment:      require("./transformers/spec-no-for-in-of-assignment"),
-  _noDuplicateProperties:    require("./transformers/spec-no-duplicate-properties"),
+  specBlockHoistFunctions:   require("./transformers/spec-block-hoist-functions"),
+  specNoForInOfAssignment:   require("./transformers/spec-no-for-in-of-assignment"),
+  specNoDuplicateProperties: require("./transformers/spec-no-duplicate-properties"),
 
   // playground
   methodBinding:             require("./transformers/playground-method-binding"),
@@ -70,8 +80,8 @@ _.each({
   generators:                require("./transformers/es6-generators"),
 
   // spec
-  _propertyLiterals:         require("./transformers/spec-property-literals"),
-  _memberExpressioLiterals:  require("./transformers/spec-member-expression-literals"),
+  specPropertyLiterals:        require("./transformers/spec-property-literals"),
+  specMemberExpressioLiterals: require("./transformers/spec-member-expression-literals"),
 
   // wrap up
   _aliasFunctions:           require("./transformers/_alias-functions"),
diff --git a/lib/6to5/util.js b/lib/6to5/util.js
index 7bfe4e5ac3..ab43d7a30e 100644
--- a/lib/6to5/util.js
+++ b/lib/6to5/util.js
@@ -212,6 +212,20 @@ exports.repeat = function (width, cha) {
   return new Array(width + 1).join(cha);
 };
 
+exports.normaliseAst = function (ast, comments, tokens) {
+  if (ast && ast.type === "Program") {
+    ast = t.file(ast, comments || [], tokens || []);
+
+    traverse(ast, function (node, parent) {
+      node._parent = parent;
+    });
+
+    return ast;
+  } else {
+    throw new Error("Not a valid ast?");
+  }
+};
+
 exports.parse = function (opts, code, callback) {
   try {
     var comments = [];
@@ -231,11 +245,7 @@ exports.parse = function (opts, code, callback) {
 
     estraverse.attachComments(ast, comments, tokens);
 
-    ast = t.file(ast, comments, tokens);
-
-    traverse(ast, function (node, parent) {
-      node._parent = parent;
-    });
+    ast = exports.normaliseAst(ast, comments, tokens);
 
     if (callback) {
       return callback(ast);