diff --git a/.gitignore b/.gitignore
index b90ffc5..c527c3a 100644
--- a/.gitignore
+++ b/.gitignore
@@ -8,4 +8,9 @@ vendor/
 .idea/
 
 # Environment files
-.env/*.*
\ No newline at end of file
+.env/*.*
+
+# Local configs
+.php_cs
+.php_cs.cache
+phpunit.xml
diff --git a/.php_cs.dist b/.php_cs.dist
new file mode 100644
index 0000000..c906f2e
--- /dev/null
+++ b/.php_cs.dist
@@ -0,0 +1,20 @@
+<?php
+
+$finder = PhpCsFixer\Finder::create()
+    ->in(__DIR__ . '/lib');
+
+return PhpCsFixer\Config::create()
+    ->setRiskyAllowed(true)
+    ->setRules([
+        '@PSR2' => true,
+        '@Symfony' => true,
+        'array_syntax' => ['syntax' => 'short'],
+        'cast_spaces' => ['space' => 'single'],
+        'yoda_style' => false,
+        'concat_space' => ['spacing' => 'one'],
+        'phpdoc_summary' => false,
+        'combine_consecutive_unsets' => true,
+        'final_internal_class' => true,
+        'global_namespace_import' => ['import_classes' => false],
+    ])
+    ->setFinder($finder);
diff --git a/.travis.yml b/.travis.yml
index 6caa598..63cbb5f 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -1,16 +1,5 @@
 language: php
 
-before_script:
-  - if [ -n "$GIT_HUB_TOKEN" ]; then composer config -g github-oauth.github.com "$GIT_HUB_TOKEN"; fi;
-  - composer install
-  - if [ "$dependencies" = "lowest" ]; then composer update --prefer-lowest --prefer-stable -n; fi;
-
-script:
-  - make test
-
-after_success:
-  - bash <(curl -s https://codecov.io/bash)
-
 php:
   - 5.6
   - 7.0
@@ -20,8 +9,26 @@ php:
   - 7.4
 
 env:
-  - dependencies=lowest
-  - dependencies=highest
+  matrix:
+    - dependencies=lowest
+    - dependencies=highest
+  global:
+    - composer_flags="--no-interaction --no-ansi --no-progress --no-suggest --verbose"
+
+before_install:
+  - composer self-update
+  - composer clear-cache
+
+install:
+  - if [ -n "$GIT_HUB_TOKEN" ]; then composer config -g github-oauth.github.com "$GIT_HUB_TOKEN"; fi;
+  - if [ "$dependencies" = "highest" ]; then composer update $composer_flags; fi;
+  - if [ "$dependencies" = "lowest" ]; then composer update $composer_flags --prefer-lowest --prefer-stable; fi;
+
+script:
+  - vendor/bin/phpunit test/unit
+
+after_success:
+  - bash <(curl -s https://codecov.io/bash)
 
 notifications:
   slack:
diff --git a/Makefile b/Makefile
index 260a6d0..8fe298f 100644
--- a/Makefile
+++ b/Makefile
@@ -4,7 +4,7 @@ clean:
 	@rm -rf vendor composer.lock
 
 install: clean
-	composer install
+	composer install --no-suggest --no-scripts --no-progress --no-interaction
 
 test: install
 	vendor/bin/phpunit test/unit
diff --git a/composer.json b/composer.json
index 146d016..8f79aeb 100644
--- a/composer.json
+++ b/composer.json
@@ -18,11 +18,14 @@
     "require": {
         "php": ">=5.6",
         "ext-curl": "*",
-        "ext-json": "*"
+        "ext-json": "*",
+        "ext-mbstring": "*"
     },
     "require-dev": {
-        "phpunit/phpunit": "~4.4",
-        "squizlabs/php_codesniffer": "~2.0"
+        "phpunit/phpunit": "^5.7",
+        "sebastian/version": "^1.0.6",
+        "squizlabs/php_codesniffer": "~2.0",
+        "friendsofphp/php-cs-fixer": "^2.16"
     },
     "autoload": {
         "psr-4": {
diff --git a/lib/Client.php b/lib/Client.php
index 2609a39..77b092c 100644
--- a/lib/Client.php
+++ b/lib/Client.php
@@ -9,9 +9,7 @@
 use SendGrid\Exception\InvalidRequest;
 
 /**
- *
  * Class Client
- * @package SendGrid
  * @version 3.9.5
  *
  * Quickly and easily access any REST or REST-like API.
@@ -76,7 +74,6 @@
  * @method Client segments()
  * @method Client singlesends()
  *
- *
  * Devices
  * @method Client devices()
  *
@@ -206,24 +203,30 @@ class Client
     protected $retryOnLimit;
 
     /**
-     * These are the supported HTTP verbs
+     * Supported HTTP verbs.
      *
      * @var array
      */
     private $methods = ['get', 'post', 'patch', 'put', 'delete'];
 
     /**
-      * Initialize the client
-      *
-      * @param string  $host          the base url (e.g. https://api.sendgrid.com)
-      * @param array   $headers       global request headers
-      * @param string  $version       api version (configurable) - this is specific to the SendGrid API
-      * @param array   $path          holds the segments of the url path
-      * @param array   $curlOptions   extra options to set during curl initialization
-      * @param bool    $retryOnLimit  set default retry on limit flag
-      */
-    public function __construct($host, $headers = null, $version = null, $path = null, $curlOptions = null, $retryOnLimit = false)
-    {
+     * Initialize the client.
+     *
+     * @param string $host         the base url (e.g. https://api.sendgrid.com)
+     * @param array  $headers      global request headers
+     * @param string $version      api version (configurable) - this is specific to the SendGrid API
+     * @param array  $path         holds the segments of the url path
+     * @param array  $curlOptions  extra options to set during curl initialization
+     * @param bool   $retryOnLimit set default retry on limit flag
+     */
+    public function __construct(
+        $host,
+        $headers = null,
+        $version = null,
+        $path = null,
+        $curlOptions = null,
+        $retryOnLimit = false
+    ) {
         $this->host = $host;
         $this->headers = $headers ?: [];
         $this->version = $version;
@@ -275,7 +278,7 @@ public function getCurlOptions()
     }
 
     /**
-     * Set extra options to set during curl initialization
+     * Set extra options to set during curl initialization.
      *
      * @param array $options
      *
@@ -289,7 +292,7 @@ public function setCurlOptions(array $options)
     }
 
     /**
-     * Set default retry on limit flag
+     * Set default retry on limit flag.
      *
      * @param bool $retry
      *
@@ -303,7 +306,7 @@ public function setRetryOnLimit($retry)
     }
 
     /**
-     * Set concurrent request flag
+     * Set concurrent request flag.
      *
      * @param bool $isConcurrent
      *
@@ -317,7 +320,7 @@ public function setIsConcurrentRequest($isConcurrent)
     }
 
     /**
-     * Build the final URL to be passed
+     * Build the final URL to be passed.
      *
      * @param array $queryParams an array of all the query parameters
      *
@@ -329,16 +332,17 @@ private function buildUrl($queryParams = null)
         if (isset($queryParams)) {
             $path .= '?' . http_build_query($queryParams);
         }
+
         return sprintf('%s%s%s', $this->host, $this->version ?: '', $path);
     }
 
     /**
      * Creates curl options for a request
-     * this function does not mutate any private variables
+     * this function does not mutate any private variables.
      *
      * @param string $method
-     * @param array $body
-     * @param array $headers
+     * @param array  $body
+     * @param array  $headers
      *
      * @return array
      */
@@ -349,7 +353,7 @@ private function createCurlOptions($method, $body = null, $headers = null)
                 CURLOPT_HEADER => true,
                 CURLOPT_CUSTOMREQUEST => strtoupper($method),
                 CURLOPT_SSL_VERIFYPEER => true,
-                CURLOPT_FAILONERROR => false
+                CURLOPT_FAILONERROR => false,
             ] + $this->curlOptions;
 
         if (isset($headers)) {
@@ -369,9 +373,8 @@ private function createCurlOptions($method, $body = null, $headers = null)
     }
 
     /**
-     * @param array $requestData
-     *      e.g. ['method' => 'POST', 'url' => 'www.example.com', 'body' => 'test body', 'headers' => []]
-     * @param bool $retryOnLimit
+     * @param array $requestData  (method, url, body and headers)
+     * @param bool  $retryOnLimit
      *
      * @return array
      */
@@ -401,9 +404,9 @@ private function createCurlMultiHandle(array $requests)
     }
 
     /**
-     * Prepare response object
+     * Prepare response object.
      *
-     * @param resource $channel  the curl resource
+     * @param resource $channel the curl resource
      * @param string   $content
      *
      * @return Response object
@@ -413,9 +416,9 @@ private function parseResponse($channel, $content)
         $headerSize = curl_getinfo($channel, CURLINFO_HEADER_SIZE);
         $statusCode = curl_getinfo($channel, CURLINFO_HTTP_CODE);
 
-        $responseBody = substr($content, $headerSize);
+        $responseBody = mb_substr($content, $headerSize);
 
-        $responseHeaders = substr($content, 0, $headerSize);
+        $responseHeaders = mb_substr($content, 0, $headerSize);
         $responseHeaders = explode("\n", $responseHeaders);
         $responseHeaders = array_map('trim', $responseHeaders);
 
@@ -423,7 +426,7 @@ private function parseResponse($channel, $content)
     }
 
     /**
-     * Retry request
+     * Retry request.
      *
      * @param array  $responseHeaders headers from rate limited response
      * @param string $method          the HTTP verb
@@ -432,12 +435,14 @@ private function parseResponse($channel, $content)
      * @param array  $headers         original headers
      *
      * @return Response response object
+     *
      * @throws InvalidRequest
      */
     private function retryRequest(array $responseHeaders, $method, $url, $body, $headers)
     {
         $sleepDurations = $responseHeaders['X-Ratelimit-Reset'] - time();
         sleep($sleepDurations > 0 ? $sleepDurations : 0);
+
         return $this->makeRequest($method, $url, $body, $headers, false);
     }
 
@@ -452,6 +457,7 @@ private function retryRequest(array $responseHeaders, $method, $url, $body, $hea
      * @param bool   $retryOnLimit should retry if rate limit is reach?
      *
      * @return Response object
+     *
      * @throws InvalidRequest
      */
     public function makeRequest($method, $url, $body = null, $headers = null, $retryOnLimit = false)
@@ -469,8 +475,9 @@ public function makeRequest($method, $url, $body = null, $headers = null, $retry
 
         $response = $this->parseResponse($channel, $content);
 
-        if ($response->statusCode() === self::TOO_MANY_REQUESTS_HTTP_CODE && $retryOnLimit) {
+        if ($retryOnLimit && $response->statusCode() === self::TOO_MANY_REQUESTS_HTTP_CODE) {
             $responseHeaders = $response->headers(true);
+
             return $this->retryRequest($responseHeaders, $method, $url, $body, $headers);
         }
 
@@ -480,7 +487,7 @@ public function makeRequest($method, $url, $body = null, $headers = null, $retry
     }
 
     /**
-     * Send all saved requests at once
+     * Send all saved requests at once.
      *
      * @param array $requests
      *
@@ -504,11 +511,10 @@ public function makeAllRequests(array $requests = [])
         $responses = [];
         $sleepDurations = 0;
         foreach ($channels as $id => $channel) {
-
             $content = curl_multi_getcontent($channel);
             $response = $this->parseResponse($channel, $content);
 
-            if ($response->statusCode() === self::TOO_MANY_REQUESTS_HTTP_CODE && $requests[$id]['retryOnLimit']) {
+            if ($requests[$id]['retryOnLimit'] && $response->statusCode() === self::TOO_MANY_REQUESTS_HTTP_CODE) {
                 $headers = $response->headers(true);
                 $sleepDurations = max($sleepDurations, $headers['X-Ratelimit-Reset'] - time());
                 $requestData = [
@@ -531,6 +537,7 @@ public function makeAllRequests(array $requests = [])
             sleep($sleepDurations > 0 ? $sleepDurations : 0);
             $responses = array_merge($responses, $this->makeAllRequests($retryRequests));
         }
+
         return $responses;
     }
 
@@ -557,20 +564,22 @@ public function _($name = null)
 
     /**
      * Dynamically add method calls to the url, then call a method.
-     * (e.g. client.name.name.method())
+     * (e.g. client.name.name.method()).
      *
      * @param string $name name of the dynamic method call or HTTP verb
      * @param array  $args parameters passed with the method call
      *
      * @return Client|Response|Response[]|null object
+     *
      * @throws InvalidRequest
      */
     public function __call($name, $args)
     {
-        $name = strtolower($name);
+        $name = mb_strtolower($name);
 
         if ($name === 'version') {
             $this->version = $args[0];
+
             return $this->_();
         }
 
@@ -579,7 +588,7 @@ public function __call($name, $args)
             return $this->makeAllRequests();
         }
 
-        if (in_array($name, $this->methods, true)) {
+        if (\in_array($name, $this->methods, true)) {
             $body = isset($args[0]) ? $args[0] : null;
             $queryParams = isset($args[1]) ? $args[1] : null;
             $url = $this->buildUrl($queryParams);
@@ -590,6 +599,7 @@ public function __call($name, $args)
                 // save request to be sent later
                 $requestData = ['method' => $name, 'url' => $url, 'body' => $body, 'headers' => $headers];
                 $this->savedRequests[] = $this->createSavedRequest($requestData, $retryOnLimit);
+
                 return null;
             }
 
diff --git a/lib/Exception/InvalidRequest.php b/lib/Exception/InvalidRequest.php
index 07c8e33..21ae2ac 100644
--- a/lib/Exception/InvalidRequest.php
+++ b/lib/Exception/InvalidRequest.php
@@ -6,17 +6,14 @@
  * Class InvalidHttpRequest
  *
  * Thrown when invalid payload was constructed, which could not reach SendGrid server.
- *
- * @package SendGrid\Exception
  */
 class InvalidRequest extends \Exception
 {
     public function __construct(
-        $message = "",
+        $message = '',
         $code = 0,
         \Exception $previous = null
-    )
-    {
+    ) {
         $message = 'Could not send request to server. ' .
             'CURL error ' . $code . ': ' . $message;
         parent::__construct($message, $code, $previous);
diff --git a/lib/Response.php b/lib/Response.php
index 9ee80da..376af50 100644
--- a/lib/Response.php
+++ b/lib/Response.php
@@ -27,11 +27,11 @@ class Response
     protected $headers;
 
     /**
-     * Setup the response data
+     * Setup the response data.
      *
-     * @param int    $statusCode the status code.
-     * @param string $body       the response body.
-     * @param array  $headers    an array of response headers.
+     * @param int    $statusCode the status code
+     * @param string $body       the response body
+     * @param array  $headers    an array of response headers
      */
     public function __construct($statusCode = 200, $body = '', array $headers = [])
     {
@@ -41,7 +41,7 @@ public function __construct($statusCode = 200, $body = '', array $headers = [])
     }
 
     /**
-     * The status code
+     * The status code.
      *
      * @return int
      */
@@ -51,7 +51,7 @@ public function statusCode()
     }
 
     /**
-     * The response body
+     * The response body.
      *
      * @return string
      */
@@ -61,7 +61,7 @@ public function body()
     }
 
     /**
-     * The response headers
+     * The response headers.
      *
      * @param bool $assoc
      *
@@ -77,19 +77,18 @@ public function headers($assoc = false)
     }
 
     /**
-      * Returns response headers as associative array
-      *
-      * @param array $headers
-      *
-      * @return array
-      */
+     * Returns response headers as associative array.
+     *
+     * @param array $headers
+     *
+     * @return array
+     */
     private function prettifyHeaders(array $headers)
     {
         return array_reduce(
             array_filter($headers),
-            function ($result, $header) {
-
-                if (false === strpos($header, ':')) {
+            static function ($result, $header) {
+                if (mb_strpos($header, ':') === false) {
                     $result['Status'] = trim($header);
 
                     return $result;
diff --git a/test/unit/ClientTest.php b/test/unit/ClientTest.php
index 4f506ec..16e8d25 100644
--- a/test/unit/ClientTest.php
+++ b/test/unit/ClientTest.php
@@ -79,7 +79,10 @@ public function testGetHost()
 
     public function testGetHeaders()
     {
-        $client = new Client('https://localhost:4010', ['Content-Type: application/json', 'Authorization: Bearer SG.XXXX']);
+        $client = new Client(
+            'https://localhost:4010',
+            ['Content-Type: application/json', 'Authorization: Bearer SG.XXXX']
+        );
         $this->assertSame(['Content-Type: application/json', 'Authorization: Bearer SG.XXXX'], $client->getHeaders());
 
         $client2 = new Client('https://localhost:4010');
@@ -92,7 +95,7 @@ public function testGetVersion()
         $this->assertSame('/v3', $client->getVersion());
 
         $client = new Client('https://localhost:4010');
-        $this->assertSame(null, $client->getVersion());
+        $this->assertNull($client->getVersion());
     }
 
     public function testGetPath()
@@ -123,7 +126,7 @@ public function testCurlMulti()
         $client->get(null, ['limit' => 100, 'offset' => 0]);
 
         // returns 3 response object
-        $this->assertEquals(3, count($client->send()));
+        $this->assertCount(3, $client->send());
     }
 
     public function testCreateCurlOptionsWithMethodOnly()
@@ -199,8 +202,9 @@ public function testCreateCurlOptionsWithBodyAndHeaders()
 
     public function testThrowExceptionOnInvalidCall()
     {
-        $this->setExpectedException(InvalidRequest::class);
-        $client = new Client('invalid://url',['User-Agent: Custom-Client 1.0']);
+        $this->expectException(InvalidRequest::class);
+
+        $client = new Client('invalid://url', ['User-Agent: Custom-Client 1.0']);
         $client->get();
     }