diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
new file mode 100644
index 0000000..3be69ca
--- /dev/null
+++ b/CONTRIBUTING.md
@@ -0,0 +1,24 @@
+# Contributing
+
+👍 First off, thanks for taking the time to contribute! 👍
+
+When contributing to this project, please first discuss the change you wish to make in an [Issue](https://github.com/enricodias/smsdev-php/issues/new).
+
+## Coding conventions
+
+-   Use the [PSR-12](https://www.php-fig.org/psr/psr-12/) coding style.
+-   Follow the PHPMD and PHPCS rules when possible.
+-   Include DocBlocks in new methods, classes and properties.
+-   Create the appropriate tests for any new feature.
+-   Update the README.md explaining new or modified features.
+-   Follow the SOLID principles.
+
+Please note, if your changes are purely to things like README, CHANGELOG etc, you can add ```[skip ci]``` as the last line of your commit message and your PR won't be run through our continuous integration systems. We ask that you use ```[skip ci]``` where appropriate as it helps to get changes through CI faster and doesn't waste resources kindly donated to the Open Source community.
+
+## Guidelines for merging
+
+-   Issue 1 Pull Request per feature. Don't lump unrelated changes together.
+-   Use the present tense ("Add feature" not "Added feature").
+-   Use the imperative mood ("Change string to..." not "Changes string to...").
+-   Limit the first line to 72 characters or less.
+-   Reference issues and pull requests liberally after the first line.
diff --git a/README.md b/README.md
index 6b43c3e..ac9eaea 100644
--- a/README.md
+++ b/README.md
@@ -1,2 +1,122 @@
 # smsdev-php
-A PHP library that wraps the smsdev.com.br API
+
+[![Build Status](https://travis-ci.com/enricodias/smsdev-php.svg?branch=master)](https://travis-ci.com/enricodias/smsdev-php)
+[![Code Coverage](https://scrutinizer-ci.com/g/enricodias/smsdev-php/badges/coverage.png?b=master)](https://scrutinizer-ci.com/g/enricodias/smsdev-php/?branch=master)
+[![Scrutinizer Code Quality](https://scrutinizer-ci.com/g/enricodias/smsdev-php/badges/quality-score.png?b=master)](https://scrutinizer-ci.com/g/enricodias/smsdev-php/?branch=master)
+[![Latest version](http://img.shields.io/packagist/v/enricodias/smsdev.svg)](https://packagist.org/packages/enricodias/smsdev)
+[![Downloads total](http://img.shields.io/packagist/dt/enricodias/smsdev.svg)](https://packagist.org/packages/enricodias/smsdev)
+[![License](http://img.shields.io/packagist/l/enricodias/smsdev.svg)](https://github.com/enricodias/smsdev-php/blob/master/LICENSE.md)
+
+Send and receive SMS using [SmsDev.com.br](https://www.smsdev.com.br)
+
+## Installation
+
+Require this package with Composer in the root directory of your project.
+
+```bash
+composer require enricodias/smsdev-php
+```
+
+## Usage
+
+Create a new instance with your API key:
+
+```php
+$SmsDev = new \enricodias\SmsDev('API_KEY');
+```
+
+Set any date format to be used in all date methods:
+
+```php
+$SmsDev->setDateFormat('Y-m-d H:i:s'); // default is 'U', timestamp
+```
+
+### Sending an SMS message
+
+```php
+$SmsDev->send(5511988881111, 'SMS Message'); // returns true if the API accepts the message
+
+var_dump($SmsDev->getResult()); // Returns the raw API response.
+```
+
+The country code optional. The default is 55 (Brazil).
+
+### Receiving SMS messages
+
+Get unread messages in a specific date interval:
+
+```php
+$SmsDev->setFilter()
+            ->isUnread()
+            ->dateBetween('2018-01-19', '2019-01-19')
+        ->fetch();
+```
+
+Search for a specific message id:
+
+```php
+$SmsDev->setFilter()
+            ->byId(2515974)
+        ->fetch();
+```
+
+### Parsing the response
+
+After fetching the messages you can either access the raw API response using ```getResult()``` or use the function ```parsedMessages()``` to get a simplified array:
+
+```php
+$SmsDev->setDateFormat('U'); // timestamp
+
+$messages = $SmsDev->parsedMessages();
+
+var_dump($messages);
+
+/*
+array(1) {
+    ['date']    => '1529418914'
+    ['number']  => '5511988887777'
+    ['message'] => 'Message'
+}
+*/
+```
+
+Dates are converted to the format specified in ```setDateFormat()```.
+
+### Date filters
+
+The following filters are equivalent:
+
+```php
+$SmsDev->setFilter()
+            ->dateBetween('2018-01-19', '2019-01-19')
+        ->fetch();
+
+$SmsDev->setFilter()
+            ->dateBetween('2018-01-19', '')
+            ->dateTo('2019-01-19')
+        ->fetch();
+
+$SmsDev->setFilter()
+            ->dateBetween('', '2019-01-19')
+            ->dateFrom('2018-01-19')
+        ->fetch();
+
+$SmsDev->setFilter()
+            ->dateFrom('2018-01-19')
+            ->dateTo('2019-01-19')
+        ->fetch();
+```
+
+## Timezone problems
+
+The API uses the timezone America/Sao_Paulo. Using another timezone in your application will force you to convert dates locally in order to get correct values.
+
+> Ex: if you are using UTC-4 and receive a new message, it will look like the message came from the future because America/Sao_Paulo is UTC-3.
+
+This class solves this problem by automatically correcting dates both in search filters and in parsed messages. Only the dates in raw API responses are not converted.
+
+## TODO
+
+-    Verify phone number locally.
+-    Check the status of sent messages.
+-    Send multiple SMS messages.
diff --git a/composer.json b/composer.json
index c4085f6..398aa09 100644
--- a/composer.json
+++ b/composer.json
@@ -2,7 +2,7 @@
     "name": "enricodias/smsdev",
     "type": "library",
     "license": "MIT",
-    "description": "A wrapper to the SmsDev.com.br API.",
+    "description": "Send and receive SMS using SmsDev.com.br",
     "keywords": ["smsdev", "sms"],
     "authors": [
         {
diff --git a/src/SmsDev.php b/src/SmsDev.php
index f5415f4..d462327 100644
--- a/src/SmsDev.php
+++ b/src/SmsDev.php
@@ -5,22 +5,68 @@
 use GuzzleHttp\Client;
 use GuzzleHttp\Psr7\Request;
 
+/**
+ * SmsDev
+ * 
+ * Send and receive SMS using SmsDev.com.br
+ * 
+ * @see https://www.smsdev.com.br/ SMSDev API.
+ * 
+ * @author Enrico Dias <enrico@enricodias.com>
+ */
 class SmsDev
 {
+    /**
+     * API url.
+     *
+     * @var string
+     */
     private $_apiUrl = 'https://api.smsdev.com.br';
 
+    /**
+     * API key.
+     *
+     * @var string
+     */
     private $_apiKey = '';
 
+    /**
+     * API timezone.
+     *
+     * @object \DateTimeZone
+     */
     private $_apiTimeZone;
 
+    /**
+     * Date format to be used in all date functions.
+     *
+     * @var string
+     */
     private $_dateFormat = 'U';
 
+    /**
+     * Query string to be sent to the API as a search filter.
+     *
+     * The default 'status' = 1 will return all received messages.
+     * 
+     * @var array
+     */
     private $_query = [
         'status' => 1
     ];
 
+    /**
+     * Raw API response/
+     *
+     * @var array
+     */
     private $_result = [];
 
+    /**
+     * Creates a new SmsDev instance with an API key and sets the default API timezone.
+     *
+     * @param string $apiKey
+     */
     public function __construct($apiKey = '')
     {
         $this->_apiKey = $apiKey;
@@ -31,11 +77,13 @@ public function __construct($apiKey = '')
     /**
      * Send an SMS message.
      * 
+     * This method does not guarantee that the recipient received the massage since the message delivery is async.
+     * 
      * TODO: verify phone number locally.
      *
-     * @param int $number
-     * @param string $message
-     * @return bool
+     * @param int $number Recipient's number.
+     * @param string $message SMS message.
+     * @return bool true if the API accepted the request.
      */
     public function send($number, $message)
     {
@@ -62,6 +110,12 @@ public function send($number, $message)
         return true;
     }
 
+    /**
+     * Sets the date format to be used in all date functions.
+     *
+     * @param string $dateFormat A valid date format (ex: Y-m-d).
+     * @return SmsDev Return itself for chaining.
+     */
     public function setDateFormat($dateFormat)
     {
         $this->_dateFormat = $dateFormat;
@@ -69,6 +123,11 @@ public function setDateFormat($dateFormat)
         return $this;
     }
 
+    /**
+     * Resets the search filter.
+     *
+     * @return SmsDev Return itself for chaining.
+     */
     public function setFilter()
     {
         $this->_query = [
@@ -78,6 +137,11 @@ public function setFilter()
         return $this;
     }
 
+    /**
+     * Sets the search filter to return unread messages only.
+     *
+     * @return SmsDev Return itself for chaining.
+     */
     public function isUnread()
     {
         $this->_query['status'] = 0;
@@ -85,6 +149,12 @@ public function isUnread()
         return $this;
     }
 
+    /**
+     * Sets the search filter to return a message with a specific id.
+     *
+     * @param int $id Message id.
+     * @return SmsDev Return itself for chaining.
+     */
     public function byId($id)
     {
         $id = intval($id);
@@ -94,21 +164,48 @@ public function byId($id)
         return $this;
     }
 
+    /**
+     * Sets the search filter to return messages older than a specific date.
+     *
+     * @param string $date A valid date.
+     * @return SmsDev Return itself for chaining.
+     */
     public function dateFrom($date)
     {
         return $this->parseDate('date_from', $date);
     }
 
+    /**
+     * Sets the search filter to return messages newer than a specific date.
+     *
+     * @param string $date A valid date.
+     * @return SmsDev Return itself for chaining.
+     */
     public function dateTo($date)
     {
         return $this->parseDate('date_to', $date);
     }
 
+    /**
+     * Sets the search filter to return messages between a specific date interval.
+     *
+     * @param string $dateFrom Minimum date.
+     * @param string $dateTo Maximum date.
+     * @return SmsDev Return itself for chaining.
+     */
     public function dateBetween($dateFrom, $dateTo)
     {
         return $this->dateFrom($dateFrom)->dateTo($dateTo);
     }
 
+    /**
+     * Query the API for received messages using search filters.
+     * 
+     * @see SmsDev::$_query Search filters.
+     * @see SmsDev::$_result API response.
+     *
+     * @return bool True if the request if the API response is valid.
+     */
     public function fetch()
     {
         $this->_result = [];
@@ -134,6 +231,15 @@ public function fetch()
         return false;
     }
 
+    /**
+     * Parse the received messages in a more useful format with the fields date, number and message.
+     * 
+     * The dates received by the API are converted to SmsDev::$_dateFormat.
+     *
+     * @see SmsDev::$_dateFormat Date format to be used in all date functions.
+     * 
+     * @return array List of received messages.
+     */
     public function parsedMessages()
     {
         $localTimeZone = new \DateTimeZone(date_default_timezone_get());
@@ -160,6 +266,11 @@ public function parsedMessages()
         return $messages;
     }
 
+    /**
+     * Get the current balance/credits.
+     *
+     * @return int Current balance in BRL cents.
+     */
     public function getBalance()
     {
         $this->_result = [];
@@ -183,11 +294,30 @@ public function getBalance()
         return (int) $this->_result['saldo_sms'];
     }
 
+    /**
+     * Get the raw API response from the last response received.
+     *
+     * @see SmsDev::$_result Raw API response.
+     * 
+     * @return array Raw API response.
+     */
     public function getResult()
     {
         return $this->_result;
     }
 
+    /**
+     * Convert a date to format supported by the API.
+     * 
+     * The API requires the date format d/m/Y, but in this class any valid date format is supported.
+     * Since the API is always using the timezone America/Sao_Paulo, this function must also do timezone conversions.
+     *
+     * @see SmsDev::$_dateFormat Date format to be used in all date functions.
+     * 
+     * @param string $key The filter key to be set as a search filter.
+     * @param string $date A valid date format.
+     * @return SmsDev Return itself for chaining.
+     */
     private function parseDate($key, $date)
     {
         $parsedDate = \DateTime::createFromFormat($this->_dateFormat, $date);
@@ -203,6 +333,12 @@ private function parseDate($key, $date)
         return $this;
     }
 
+    /**
+     * Sends a request to the smsdev.com.br API.
+     *
+     * @param \GuzzleHttp\Psr7\Request $request Request object.
+     * @return bool True if the API response is valid.
+     */
     private function makeRequest($request)
     {
         $client = $this->getGuzzleClient();