diff --git a/commands/by.js b/commands/by.js
index 7bdd8f4..b9d0568 100644
--- a/commands/by.js
+++ b/commands/by.js
@@ -1,6 +1,8 @@
 /* @flow */
 
 const { analyze, print, getStats } = require("../lib");
+const validate = require("../lib/validate");
+const { log, invalidStatsJson } = require("../lib/messages");
 
 module.exports = function byCommand(
   statsFilePath /*: string */,
@@ -8,6 +10,12 @@ module.exports = function byCommand(
   pattern /*: string */
 ) {
   const stats = getStats(statsFilePath);
+
+  if (!validate(stats)) {
+    log(invalidStatsJson(statsFilePath));
+    process.exit(1);
+  }
+
   const ignore = flags.ignore ? flags.ignore.split(",") : [];
   const report = analyze(stats, ignore).filter(mod => {
     return (
diff --git a/commands/default.js b/commands/default.js
index 56c922f..1392fd3 100644
--- a/commands/default.js
+++ b/commands/default.js
@@ -2,6 +2,8 @@
 
 const mm = require("micromatch");
 const { analyze, print, getStats } = require("../lib");
+const validate = require("../lib/validate");
+const { log, invalidStatsJson } = require("../lib/messages");
 
 /*::
 type Flags = {
@@ -22,6 +24,12 @@ module.exports = function defaultCommand(
   pattern /*: string*/
 ) {
   const stats = getStats(statsFilePath);
+
+  if (!validate(stats)) {
+    log(invalidStatsJson(statsFilePath));
+    process.exit(1);
+  }
+
   const ignore = flags.ignore ? flags.ignore.split(",") : [];
   const report = analyze(stats, ignore).filter(module => {
     if (pattern && mm.isMatch(module.name, pattern)) {
diff --git a/fixtures/invalid-no-reasons.json b/fixtures/invalid-no-reasons.json
new file mode 100644
index 0000000..5bbed6b
--- /dev/null
+++ b/fixtures/invalid-no-reasons.json
@@ -0,0 +1,13 @@
+{
+  "chunks": [
+    {
+      "modules": [
+        {
+          "id": "module1",
+          "name": "module-name",
+          "size": 500
+        }
+      ]
+    }
+  ]
+}
diff --git a/fixtures/valid.json b/fixtures/valid.json
new file mode 100644
index 0000000..cc2ed3d
--- /dev/null
+++ b/fixtures/valid.json
@@ -0,0 +1,14 @@
+{
+  "chunks": [
+    {
+      "modules": [
+        {
+          "id": "module1",
+          "name": "module-name",
+          "size": 500,
+          "reasons": []
+        }
+      ]
+    }
+  ]
+}
diff --git a/lib/utils/__tests__/get-stats.js b/lib/__tests__/get-stats.js
similarity index 100%
rename from lib/utils/__tests__/get-stats.js
rename to lib/__tests__/get-stats.js
diff --git a/lib/__tests__/validate.js b/lib/__tests__/validate.js
new file mode 100644
index 0000000..c9a27b1
--- /dev/null
+++ b/lib/__tests__/validate.js
@@ -0,0 +1,20 @@
+const test = require("ava");
+const fixtures = require("fixturez");
+const f = fixtures(__dirname);
+const validate = require("../validate");
+const getStats = require("../get-stats");
+
+test(`should return false for an invalid stats file that doesn't have "reasons" for modules`, t => {
+  const stats = getStats(f.find("invalid-no-reasons.json"));
+  t.falsy(validate(stats));
+});
+
+test(`should return false for an invalid stats file that doesn't have niether chunks nor modules`, t => {
+  const stats = getStats(f.find("empty-stats.json"));
+  t.falsy(validate(stats));
+});
+
+test("should return true for a valid stats file", t => {
+  const stats = getStats(f.find("valid.json"));
+  t.truthy(validate(stats));
+});
diff --git a/lib/analyze.js b/lib/analyze.js
index 2ae9884..5302da9 100644
--- a/lib/analyze.js
+++ b/lib/analyze.js
@@ -1,7 +1,8 @@
 /* @flow */
 /*::
 export type WebpackStats = {
-  chunks: Array<WebpackChunk>
+  chunks?: Array<WebpackChunk>,
+  modules: Array<WebpackModule>
 };
 
 export type WebpackChunk = {
@@ -93,7 +94,9 @@ const getModuleType = (name /*: string */) =>
   name.startsWith("multi ") ? "entry" : isNodeModules(name) ? "module" : "file";
 
 const flattenChunks = (stats /*: WebpackStats */) /*: Array<WebpackModule> */ =>
-  stats.chunks.reduce((modules, chunk) => modules.concat(chunk.modules), []);
+  stats.chunks
+    ? stats.chunks.reduce((modules, chunk) => modules.concat(chunk.modules), [])
+    : stats.modules;
 
 const isNodeModules = (identifier /*: string */) =>
   identifier.indexOf("node_modules") > -1;
diff --git a/lib/utils/get-stats.js b/lib/get-stats.js
similarity index 90%
rename from lib/utils/get-stats.js
rename to lib/get-stats.js
index b03ff23..2bd7067 100644
--- a/lib/utils/get-stats.js
+++ b/lib/get-stats.js
@@ -3,7 +3,7 @@
 const path = require("path");
 
 /*::
-import type { WebpackStats } from '../analyze';
+import type { WebpackStats } from './analyze';
 */
 
 const getAbsoultePath = (filePath /*: string */) =>
diff --git a/lib/index.js b/lib/index.js
index f12de8c..a0ce257 100644
--- a/lib/index.js
+++ b/lib/index.js
@@ -2,6 +2,6 @@
 
 const analyze = require("./analyze");
 const print = require("./print");
-const getStats = require("./utils/get-stats");
+const getStats = require("./get-stats");
 
 module.exports = { analyze, print, getStats };
diff --git a/lib/messages.js b/lib/messages.js
new file mode 100644
index 0000000..b3a6ce0
--- /dev/null
+++ b/lib/messages.js
@@ -0,0 +1,32 @@
+/* @flow */
+
+const chalk = require("chalk");
+
+function log(msg /*: Array<string> */) {
+  console.log(msg.join("\n"));
+}
+
+function redBadge(label /*: string*/) {
+  return chalk.bgRed.black(` ${label} `);
+}
+
+function errorBadge() {
+  return redBadge("ERROR");
+}
+
+function invalidStatsJson(file /*: string */) {
+  return [
+    chalk.red(
+      `${errorBadge()} Stats file ${chalk.bold(
+        `"${file}"`
+      )} doesn't contain "reasons" why modules are included...`
+    ),
+    `${chalk.yellow("Whybundled")} needs "reasons" to function properly.`,
+    "",
+    `To add reason check webpack documentation about stats configuration: ${chalk.blue(
+      "https://webpack.js.org/configuration/stats/#stats"
+    )}`
+  ];
+}
+
+module.exports = { log, invalidStatsJson };
diff --git a/lib/validate.js b/lib/validate.js
new file mode 100644
index 0000000..6887ded
--- /dev/null
+++ b/lib/validate.js
@@ -0,0 +1,28 @@
+/* @flow */
+
+/*::
+import type { WebpackStats } from "./analyze";
+*/
+
+function has(obj) {
+  return function(prop) {
+    return obj.hasOwnProperty(prop);
+  };
+}
+
+function isValidModule(sample) {
+  const isProp = has(sample);
+  if (!isProp("reasons")) return false;
+  return true;
+}
+
+module.exports = function vlidateStatsJson(stats /*: WebpackStats */) {
+  if (
+    !stats ||
+    ((!stats.chunks || !stats.chunks[0].modules) && !stats.modules)
+  ) {
+    return false;
+  }
+  const samples = (stats.modules || stats.chunks[0].modules).slice(0, 10);
+  return samples.some(isValidModule);
+};