diff --git a/lib/index.js b/lib/index.js
index 02d8dc3..0a64a9a 100644
--- a/lib/index.js
+++ b/lib/index.js
@@ -12,25 +12,34 @@ Promise.promisifyAll(dir);
 Promise.promisifyAll(SwaggerParser);
 
 var constraints = {
+  requireCurrentVersion: {
+    inclusion: {
+      within: [true, false],
+      message: "'%{value}' is not allowed"
+    }
+  },
   visibilityFilter: {
-    exclusion: {
+    inclusion: {
       within: ["EXTERNAL", "INTERNAL"],
       message: "'%{value}' is not allowed"
     }
   },
   statusFilter: {
-    exclusion: {
+    inclusion: {
       within: ["PROPOSED", "IN_DEVELOPMENT", "RELEASED"],
       message: "'%{value}' is not allowed"
     }
-  },
-  stripExtensions: {
-    
   }
 };
 
 exports.preparePromise = function(specDir, specFile, infoFile, host, schemes, basePath, options) {
-  validate(options, constraints);
+  var validationResult = validate(options, constraints);
+  if (validationResult) {
+    return Promise.reject("*** Invalid options:\n  " + _.reduce(Object.keys(validationResult), (result, key) => {
+      return result + (key + ":\n    " + validationResult[key].join("\n    "));
+    }, ""))
+  }
+  
   return dir.promiseFiles(specDir)
   .then((files) => {
     return files.filter(function(file) {
@@ -61,39 +70,63 @@ exports.preparePromise = function(specDir, specFile, infoFile, host, schemes, ba
     unsorted.tags = _.sortBy(unsorted.tags, 'name');
     return unsorted;
   })
-  .then((sorted) => { 
-    if (options.visibilityFilter && options.statusFilter) {
+  .then((sorted) => {
+    if (options.requireCurrentVersion) {
       paths = sorted.paths;
+      pathsWithoutVersion = [];
       _.forIn(paths, function(value, path) {
+        version = _.get(value, "x-current-version", null);
+        if (!version) {
+          pathsWithoutVersion.push(path);
+        }
+      })
+
+      if (pathsWithoutVersion) {
+        return Promise.reject("*** Missing 'x-current-version'. Paths affected:\n" + pathsWithoutVersion.join("\n")); 
+      }
+    }
+
+    return sorted;
+  })
+  .then((sorted) => { 
+    paths = sorted.paths;
+    _.forIn(paths, function(value, path) {
+      // check visibility
+      if (options.visibilityFilter) {
         visibility = _.get(value, "x-visibility", "");
-        stat = _.get(value, "x-status", "");
         if (visibility !== options.visibilityFilter || visibility === "") {
           delete sorted.paths[path];
         }
-        if (stat !== options.statusFilter || stat === "") {
+      }
+
+      // check status
+      if (options.statusFilter) {
+        status = _.get(value, "x-status", "");
+        
+        if (status !== options.statusFilter || status === "") {
           delete sorted.paths[path];
         }
-      });
-    }
+      }
+    });
     return sorted;
   })
   .catch(e => {
-    Promise.reject(e);
+    return Promise.reject(e);
   });
 }
 
 exports.prepare = function(specDir, specFile, infoFile, host, schemes, basePath, options, callback) {
   this.preparePromise(specDir, specFile, infoFile, host, schemes, basePath, options)
   .then((apis) => {
-    callback(null, apis);
+    callback(apis, null);
   })
   .catch(e => {
-    callback(e, null);  
+    callback(null, e);  
   });
 }
 
 exports.write = function(specDir, specFile, infoFile, host, schemes, basePath, outputFile, options, callback) {
-  this.preparePromise(specDir, specFile, infoFile, host, schemes, basePath, outputFile, options)
+  this.preparePromise(specDir, specFile, infoFile, host, schemes, basePath, options)
   .then((apis) => {
     fs.writeFileAsync(outputFile, JSON.stringify(apis), {})
     .then(() => {
@@ -101,6 +134,6 @@ exports.write = function(specDir, specFile, infoFile, host, schemes, basePath, o
     });
   })
   .catch(e => {
-    callback(e, null);  
+    callback(e);  
   });
 }