diff --git a/.gitignore b/.gitignore
index 8280239..6ed9d8d 100644
--- a/.gitignore
+++ b/.gitignore
@@ -12,4 +12,5 @@ results
 
 node_modules
 npm-debug.log
-coverage/
+coverage
+.idea
diff --git a/README.md b/README.md
index c78ef4d..611f137 100644
--- a/README.md
+++ b/README.md
@@ -7,17 +7,6 @@ koa-locales
 [![David deps][david-image]][david-url]
 [![npm download][download-image]][download-url]
 
-[npm-image]: https://img.shields.io/npm/v/koa-locales.svg?style=flat-square
-[npm-url]: https://npmjs.org/package/koa-locales
-[travis-image]: https://img.shields.io/travis/koajs/locales.svg?style=flat-square
-[travis-url]: https://travis-ci.org/koajs/locales
-[cov-image]: https://codecov.io/github/koajs/locales/coverage.svg?branch=master
-[cov-url]: https://codecov.io/github/koajs/locales?branch=master
-[david-image]: https://img.shields.io/david/koajs/locales.svg?style=flat-square
-[david-url]: https://david-dm.org/koajs/locales
-[download-image]: https://img.shields.io/npm/dm/koa-locales.svg?style=flat-square
-[download-url]: https://npmjs.org/package/koa-locales
-
 koa locales, i18n solution for koa:
 
 1. All locales resources location on `options.dirs`.
@@ -57,7 +46,7 @@ Patch locales functions to koa app.
   - {String} defaultLocale: default locale. Optional, default is `en-US`.
   - {String} queryField: locale field name on query. Optional, default is `locale`.
   - {String} cookieField: locale field name on cookie. Optional, default is `locale`.
-  - {Object} localeAlias: locale cookie value map. Optional, default is {}.
+  - {Object} localeAlias: locale value map. Optional, default is {}.
   - {String|Number} cookieMaxAge: set locale cookie value max age. Optional, default is `1y`, expired after one year.
 
 ```js
@@ -65,7 +54,20 @@ locales({
   app: app,
   dirs: [__dirname + '/app/locales'],
   defaultLocale: 'zh-CN',
-}));
+});
+```
+
+#### Aliases
+
+The key `options.localeAlias` allows to not repeat dictionary files, as you can configure to use the same file for *es_ES* for *es*, or *en_UK* for *en*.
+
+```js
+locales({
+	localeAlias: {
+		es: es_ES,
+		en: en_UK
+	}
+});
 ```
 
 ### `context.__(key[, value1[, value2, ...]])`
@@ -102,15 +104,62 @@ __('{a} {a} {b} {b} {b}', {a: 'foo', b: 'bar'})
 this.state.__ = this.__.bind(this);
 ```
 
-[nunjucks] example:
+[Nunjucks] example:
 
 ```html
 {{ __('Hello, %s', user.name) }}
 ```
 
+[Pug] example:
+
+```pug
+p= __('Hello, %s', user.name)
+```
+
+[Koa-pug] integration:
+
+You can set the property *locals* on the KoaPug instance, where the default locals are stored.
+
+```js
+app.use(async (ctx, next) => {
+    koaPug.locals.__ = ctx.__.bind(ctx);
+    await next()
+});
+```
+
+## Debugging
+
+If you are interested on knowing what locale was chosen and why you can enable the debug messages from [debug].
+
+There is two level of verbosity:
+
+```sh
+$ DEBUG=koa-locales node .
+```
+With this line it only will show one line per request, with the chosen language and the origin where the locale come from (queryString, header or cookie).
+
+```sh
+$ DEBUG=koa-locales:silly node .
+```
+Use this level if something doesn't work as you expect. This is going to debug everything, including each translated line of text.
+
 ## License
 
 [MIT](LICENSE)
 
 
 [nunjucks]: https://www.npmjs.com/package/nunjucks
+[debug]: https://www.npmjs.com/package/debug
+[pug]: https://www.npmjs.com/package/pug
+[koa-pug]: https://www.npmjs.com/package/koa-pug
+
+[npm-image]: https://img.shields.io/npm/v/koa-locales.svg?style=flat-square
+[npm-url]: https://npmjs.org/package/koa-locales
+[travis-image]: https://img.shields.io/travis/koajs/locales.svg?style=flat-square
+[travis-url]: https://travis-ci.org/koajs/locales
+[cov-image]: https://codecov.io/github/koajs/locales/coverage.svg?branch=master
+[cov-url]: https://codecov.io/github/koajs/locales?branch=master
+[david-image]: https://img.shields.io/david/koajs/locales.svg?style=flat-square
+[david-url]: https://david-dm.org/koajs/locales
+[download-image]: https://img.shields.io/npm/dm/koa-locales.svg?style=flat-square
+[download-url]: https://npmjs.org/package/koa-locales
\ No newline at end of file
diff --git a/index.js b/index.js
index 07e7b84..d8a1981 100644
--- a/index.js
+++ b/index.js
@@ -1,6 +1,8 @@
 'use strict';
 
-const debug = require('debug')('koa-locales');
+const Debug = require('debug');
+const debug = Debug('koa-locales');
+const debugSilly = Debug('koa-locales:silly');
 const ini = require('ini');
 const util = require('util');
 const fs = require('fs');
@@ -64,7 +66,7 @@ module.exports = function (app, options) {
     }
   }
 
-  debug('init locales with %j, got %j resources', options, Object.keys(resources));
+  debug('Init locales with %j, got %j resources', options, Object.keys(resources));
 
   app.context[functionName] = function (key, value) {
     if (arguments.length === 0) {
@@ -80,7 +82,7 @@ module.exports = function (app, options) {
       text = key;
     }
 
-    debug('%s: %j => %j', locale, key, text);
+    debugSilly('%s: %j => %j', locale, key, text);
     if (!text) {
       return '';
     }
@@ -128,7 +130,18 @@ module.exports = function (app, options) {
     }
 
     const cookieLocale = this.cookies.get(cookieField, { signed: false });
-    let locale = this.query[queryField] || cookieLocale;
+
+    // 1. Query
+    let locale = this.query[queryField];
+    let localeOrigin = 'query';
+
+    // 2. Cookie
+    if (!locale) {
+      locale = cookieLocale;
+      localeOrigin = 'cookie';
+    }
+
+    // 3. Header
     if (!locale) {
       // Accept-Language: zh-CN,zh;q=0.5
       // Accept-Language: zh-CN
@@ -143,32 +156,36 @@ module.exports = function (app, options) {
               const lang = formatLocale(languages[i]);
               if (resources[lang] || localeAlias[lang]) {
                 locale = lang;
+                localeOrigin = 'header';
                 break;
               }
             }
-            if (!locale) {
-              // set the first one
-              locale = languages[0];
-            }
           }
         } else {
           locale = languages;
+          localeOrigin = 'header (only one accepted language)';
         }
       }
 
       // all missing, set it to defaultLocale
       if (!locale) {
         locale = defaultLocale;
+        localeOrigin = 'default';
       }
     }
 
     // cookie alias
-    if (locale in localeAlias) locale = localeAlias[locale];
+    if (locale in localeAlias) {
+      const originalLocale = locale;
+      locale = localeAlias[locale];
+      debugSilly('Used alias, received %s but using %s', originalLocale, locale);
+    }
 
     locale = formatLocale(locale);
 
     // validate locale
     if (!resources[locale]) {
+      debugSilly('Locale %s is not supported. Using default (%s)', locale, defaultLocale);
       locale = defaultLocale;
     }
 
@@ -181,7 +198,10 @@ module.exports = function (app, options) {
         maxAge: cookieMaxAge,
         signed: false,
       });
+      debugSilly('Saved cookie with locale %s', locale);
     }
+    debug('Locale: %s from %s', locale, localeOrigin);
+    debugSilly('Locale: %s from %s', locale, localeOrigin);
     this.__locale = locale;
     return locale;
   };