diff --git a/.github/CONTRIBUTING.md b/.github/CONTRIBUTING.md
index 035bb58..96c8d03 100644
--- a/.github/CONTRIBUTING.md
+++ b/.github/CONTRIBUTING.md
@@ -9,7 +9,6 @@ find below useful information about how to contribute to the Gotenberg PHP clien
 
 1. Fork this repository
 2. Install Docker and Docker Compose.
-3. Install the latest [Orbit](https://github.com/gulien/orbit) release
 
 ### Working with git
 
diff --git a/.github/PULL_REQUEST_TEMPLATE.md b/.github/PULL_REQUEST_TEMPLATE.md
index a2838dc..aeb0bf0 100644
--- a/.github/PULL_REQUEST_TEMPLATE.md
+++ b/.github/PULL_REQUEST_TEMPLATE.md
@@ -37,8 +37,8 @@ Fixes #
 **Checklist**
 
 - [ ] Have you followed the guidelines in our [CONTRIBUTING](CONTRIBUTING.md) guide?
-- [ ] Have you lint your code locally prior to submission (`orbit run lint`)?
+- [ ] Have you lint your code locally prior to submission (`make lint`)?
 - [ ] Have you written new tests for your core changes, as applicable?
-- [ ] Have you successfully ran tests with your changes locally (`orbit run up ci`)?
+- [ ] Have you successfully ran tests with your changes locally (`make tests`)?
 - [ ] I have squashed any insignificant commits
 - [ ] This change has comments for package types, values, functions, and non-obvious lines of code
\ No newline at end of file
diff --git a/.travis.yml b/.travis.yml
index e9369a9..61b853e 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -5,12 +5,6 @@ language: generic
 services:
   - docker
 
-before_install:
-  - wget -qO- https://github.com/gulien/orbit/releases/download/v3.0.1/orbit_Linux_x86_64.tar.gz | tar xvz -C .
-  - sudo mv ./orbit /usr/local/bin && chmod +x /usr/local/bin/orbit
-
-before_script:
-  - orbit run up
-
 script:
-  - orbit run lint tests
\ No newline at end of file
+  - make lint
+  - make tests
\ No newline at end of file
diff --git a/LICENSE b/LICENSE
index 4188a9b..b756c5a 100644
--- a/LICENSE
+++ b/LICENSE
@@ -1,6 +1,6 @@
 MIT License
 
-Copyright (c) 2018 TheCodingMachine
+Copyright (c) 2019 TheCodingMachine
 
 Permission is hereby granted, free of charge, to any person obtaining a copy
 of this software and associated documentation files (the "Software"), to deal
diff --git a/Makefile b/Makefile
new file mode 100644
index 0000000..761b078
--- /dev/null
+++ b/Makefile
@@ -0,0 +1,16 @@
+# start workspace.
+workspace:
+	docker-compose run --rm php bash
+
+# run all linters.
+lint:
+	docker-compose run --rm -T php composer install
+	docker-compose run --rm -T php composer run csfix
+	docker-compose run --rm -T php composer run cscheck
+	docker-compose run --rm -T php composer run phpstan
+
+# run all tests.
+test:
+	docker-compose up -d gotenberg
+	docker-compose run --rm -T php composer run phpunit
+	docker-compose down
\ No newline at end of file
diff --git a/composer.json b/composer.json
index b1e6b27..2efdd58 100644
--- a/composer.json
+++ b/composer.json
@@ -38,7 +38,8 @@
     "thecodingmachine/phpstan-safe-rule": "^0.1.0",
     "thecodingmachine/phpstan-strict-rules": "^0.10.7",
     "php-http/mock-client": "^1.0",
-    "php-http/guzzle6-adapter": "^1.1"
+    "php-http/guzzle6-adapter": "^1.1",
+    "doctrine/coding-standard": "^6.0"
   },
   "autoload" : {
     "psr-4" : {
@@ -51,14 +52,14 @@
     }
   },
   "scripts": {
-    "cs-fix": "phpcbf",
-    "cs-check": "phpcs",
+    "csfix": "phpcbf",
+    "cscheck": "phpcs",
     "phpstan": "phpstan analyse src -c phpstan.neon --level=7 --no-progress -vvv",
     "phpunit": "phpunit --configuration phpunit.xml.dist"
   },
   "extra": {
     "branch-alias": {
-      "dev-master": "3.0.x-dev"
+      "dev-master": "6.0.x-dev"
     }
   }
 }
diff --git a/docker-compose.yml b/docker-compose.yml
index ef8000c..c396faf 100644
--- a/docker-compose.yml
+++ b/docker-compose.yml
@@ -3,7 +3,7 @@ version: '3'
 services:
 
   php:
-    image: thecodingmachine/php:7.2-v2-cli
+    image: thecodingmachine/php:7.3-v2-cli
     container_name: php
     environment:
       - PHP_EXTENSION_XDEBUG=1
@@ -12,6 +12,6 @@ services:
       - ./:/usr/src/app:rw
 
   gotenberg:
-    image: thecodingmachine/gotenberg:5.0.0
+    image: thecodingmachine/gotenberg:6.0.0
     container_name: gotenberg
     restart: 'no'
\ No newline at end of file
diff --git a/orbit.yml b/orbit.yml
deleted file mode 100644
index 6a9a89f..0000000
--- a/orbit.yml
+++ /dev/null
@@ -1,24 +0,0 @@
-tasks:
-
-  - use: up
-    short: Starts the CI stack
-    run:
-      - docker-compose up -d gotenberg
-
-  - use: down
-    short: Stops the CI stack
-    run:
-      - docker-compose down
-
-  - use: lint
-    shorts: Runs linter inside a container
-    run:
-      - docker-compose run --rm -T php composer install
-      - docker-compose run --rm -T php composer run cs-fix
-      - docker-compose run --rm -T php composer run cs-check
-      - docker-compose run --rm -T php composer run phpstan
-
-  - use: tests
-    short: Runs tests inside a container
-    run:
-      - docker-compose run --rm -T php composer run phpunit
\ No newline at end of file
diff --git a/phpcs.xml.dist b/phpcs.xml.dist
index d9bb9d0..8dab83a 100644
--- a/phpcs.xml.dist
+++ b/phpcs.xml.dist
@@ -1,21 +1,45 @@
 <?xml version="1.0"?>
-<ruleset name="Expressive Skeleton coding standard">
-    <description>Expressive Skeleton coding standard</description>
-
-    <!-- display progress -->
-    <arg value="p"/>
+<ruleset>
+    <arg name="basepath" value="."/>
+    <arg name="extensions" value="php"/>
+    <arg name="parallel" value="16"/>
     <arg name="colors"/>
 
-    <!-- inherit rules from: -->
-    <rule ref="PSR2"/>
+    <!-- Ignore warnings, show progress of the run and show sniff names -->
+    <arg value="nps"/>
 
-    <!-- Paths to check -->
+    <!-- Directories to be checked -->
     <file>src</file>
+    <file>tests</file>
+
+    <exclude-pattern>tests/dependencies/*</exclude-pattern>
+
+    <!-- Include full Doctrine Coding Standard -->
+    <rule ref="Doctrine">
+        <exclude name="SlevomatCodingStandard.Classes.SuperfluousInterfaceNaming.SuperfluousSuffix"/>
+        <exclude name="SlevomatCodingStandard.Classes.SuperfluousExceptionNaming.SuperfluousSuffix"/>
+        <exclude name="SlevomatCodingStandard.Classes.SuperfluousAbstractClassNaming.SuperfluousPrefix"/>
+        <exclude name="Squiz.Commenting.FunctionComment.InvalidNoReturn" />
+        <exclude name="Generic.Formatting.MultipleStatementAlignment" />
+    </rule>
+
+    <!-- Do not align assignments -->
+    <rule ref="Generic.Formatting.MultipleStatementAlignment">
+        <severity>0</severity>
+    </rule>
+
+    <!-- Do not align comments -->
+    <rule ref="Squiz.Commenting.FunctionComment.SpacingAfterParamName">
+        <severity>0</severity>
+    </rule>
+    <rule ref="Squiz.Commenting.FunctionComment.SpacingAfterParamType">
+        <severity>0</severity>
+    </rule>
 
-    <rule ref="Generic.Files.LineLength">
+    <!-- Require no space before colon in return types -->
+    <rule ref="SlevomatCodingStandard.TypeHints.ReturnTypeHintSpacing">
         <properties>
-            <property name="lineLimit" value="300"/>
-            <property name="absoluteLineLimit" value="500"/>
+            <property name="spacesCountBeforeColon" value="0"/>
         </properties>
     </rule>
-</ruleset>
+</ruleset>
\ No newline at end of file
diff --git a/src/ChromeRequest.php b/src/ChromeRequest.php
index a1bac5e..b9da5f8 100644
--- a/src/ChromeRequest.php
+++ b/src/ChromeRequest.php
@@ -1,7 +1,11 @@
 <?php
 
+declare(strict_types=1);
+
 namespace TheCodingMachine\Gotenberg;
 
+use function count;
+
 abstract class ChromeRequest extends Request implements GotenbergRequestInterface
 {
     private const WAIT_DELAY = 'waitDelay';
@@ -49,28 +53,29 @@ abstract class ChromeRequest extends Request implements GotenbergRequestInterfac
     public function getFormValues(): array
     {
         $values = parent::getFormValues();
-        if (!is_null($this->waitDelay)) {
+        if ($this->waitDelay !== null) {
             $values[self::WAIT_DELAY] = $this->waitDelay;
         }
-        if (!is_null($this->paperWidth)) {
+        if ($this->paperWidth !== null) {
             $values[self::PAPER_WIDTH] = $this->paperWidth;
         }
-        if (!is_null($this->paperHeight)) {
+        if ($this->paperHeight !== null) {
             $values[self::PAPER_HEIGHT] = $this->paperHeight;
         }
-        if (!is_null($this->marginTop)) {
+        if ($this->marginTop !== null) {
             $values[self::MARGIN_TOP] = $this->marginTop;
         }
-        if (!is_null($this->marginBottom)) {
+        if ($this->marginBottom !== null) {
             $values[self::MARGIN_BOTTOM] = $this->marginBottom;
         }
-        if (!is_null($this->marginLeft)) {
+        if ($this->marginLeft !== null) {
             $values[self::MARGIN_LEFT] = $this->marginLeft;
         }
-        if (!is_null($this->marginRight)) {
+        if ($this->marginRight !== null) {
             $values[self::MARGIN_RIGHT] = $this->marginRight;
         }
         $values[self::LANDSCAPE] = $this->landscape;
+
         return $values;
     }
 
@@ -80,18 +85,16 @@ public function getFormValues(): array
     public function getFormFiles(): array
     {
         $files = [];
-        if (!empty($this->header)) {
+        if (! empty($this->header)) {
             $files['header.html'] = $this->header;
         }
-        if (!empty($this->footer)) {
+        if (! empty($this->footer)) {
             $files['footer.html'] = $this->footer;
         }
+
         return $files;
     }
 
-    /**
-     * @param float|null $waitDelay
-     */
     public function setWaitDelay(?float $waitDelay): void
     {
         $this->waitDelay = $waitDelay;
@@ -99,6 +102,7 @@ public function setWaitDelay(?float $waitDelay): void
 
     /**
      * @param float[] $paperSize
+     *
      * @throws RequestException
      */
     public function setPaperSize(array $paperSize): void
@@ -112,6 +116,7 @@ public function setPaperSize(array $paperSize): void
 
     /**
      * @param float[] $margins
+     *
      * @throws RequestException
      */
     public function setMargins(array $margins): void
@@ -125,73 +130,46 @@ public function setMargins(array $margins): void
         $this->marginRight = $margins[3];
     }
 
-    /**
-     * @param Document|null $header
-     */
     public function setHeader(?Document $header): void
     {
         $this->header = $header;
     }
 
-    /**
-     * @param Document|null $footer
-     */
     public function setFooter(?Document $footer): void
     {
         $this->footer = $footer;
     }
 
-    /**
-     * @param float|null $paperWidth
-     */
     public function setPaperWidth(?float $paperWidth): void
     {
         $this->paperWidth = $paperWidth;
     }
 
-    /**
-     * @param float|null $paperHeight
-     */
     public function setPaperHeight(?float $paperHeight): void
     {
         $this->paperHeight = $paperHeight;
     }
 
-    /**
-     * @param float|null $marginTop
-     */
     public function setMarginTop(?float $marginTop): void
     {
         $this->marginTop = $marginTop;
     }
 
-    /**
-     * @param float|null $marginBottom
-     */
     public function setMarginBottom(?float $marginBottom): void
     {
         $this->marginBottom = $marginBottom;
     }
 
-    /**
-     * @param float|null $marginLeft
-     */
     public function setMarginLeft(?float $marginLeft): void
     {
         $this->marginLeft = $marginLeft;
     }
 
-    /**
-     * @param float|null $marginRight
-     */
     public function setMarginRight(?float $marginRight): void
     {
         $this->marginRight = $marginRight;
     }
 
-    /**
-     * @param bool $landscape
-     */
     public function setLandscape(bool $landscape): void
     {
         $this->landscape = $landscape;
diff --git a/src/Client.php b/src/Client.php
index da69755..7681ec1 100644
--- a/src/Client.php
+++ b/src/Client.php
@@ -1,7 +1,10 @@
 <?php
 
+declare(strict_types=1);
+
 namespace TheCodingMachine\Gotenberg;
 
+use Exception;
 use GuzzleHttp\Psr7\MultipartStream;
 use Http\Client\HttpClient;
 use Http\Discovery\HttpClientDiscovery;
@@ -9,9 +12,9 @@
 use Psr\Http\Message\RequestInterface;
 use Psr\Http\Message\ResponseInterface;
 use Safe\Exceptions\FilesystemException;
+use function Safe\fclose;
 use function Safe\fopen;
 use function Safe\fwrite;
-use function Safe\fclose;
 
 final class Client
 {
@@ -21,12 +24,7 @@ final class Client
     /** @var string */
     private $apiURL;
 
-    /**
-     * Client constructor.
-     * @param string $apiURL
-     * @param HttpClient|null $client
-     */
-    public function __construct(string $apiURL, HttpClient $client = null)
+    public function __construct(string $apiURL, ?HttpClient $client = null)
     {
         $this->apiURL = $apiURL;
         $this->client = $client ?: HttpClientDiscovery::find();
@@ -35,10 +33,8 @@ public function __construct(string $apiURL, HttpClient $client = null)
     /**
      * Sends the given documents to the API and returns the response.
      *
-     * @param GotenbergRequestInterface $request
-     * @return ResponseInterface
      * @throws ClientException
-     * @throws \Exception
+     * @throws Exception
      */
     public function post(GotenbergRequestInterface $request): ResponseInterface
     {
@@ -48,10 +44,8 @@ public function post(GotenbergRequestInterface $request): ResponseInterface
     /**
      * Sends the given documents to the API, stores the resulting PDF in the given destination.
      *
-     * @param GotenbergRequestInterface $request
-     * @param string $destination
      * @throws ClientException
-     * @throws \Exception
+     * @throws Exception
      * @throws FilesystemException
      */
     public function store(GotenbergRequestInterface $request, string $destination): void
@@ -59,14 +53,10 @@ public function store(GotenbergRequestInterface $request, string $destination):
         $response = $this->handleResponse($this->client->sendRequest($this->makeMultipartFormDataRequest($request)));
         $fileStream = $response->getBody();
         $fp = fopen($destination, 'w');
-        fwrite($fp, $fileStream);
+        fwrite($fp, $fileStream->getContents());
         fclose($fp);
     }
 
-    /**
-     * @param GotenbergRequestInterface $request
-     * @return RequestInterface
-     */
     private function makeMultipartFormDataRequest(GotenbergRequestInterface $request): RequestInterface
     {
         $multipartData = [];
@@ -84,11 +74,12 @@ private function makeMultipartFormDataRequest(GotenbergRequestInterface $request
             $multipartData[] = [
                 'name' => 'files',
                 'filename' => $filename,
-                'contents' => $document->getFileStream()
+                'contents' => $document->getFileStream(),
             ];
         }
         $body = new MultipartStream($multipartData);
         $messageFactory = MessageFactoryDiscovery::find();
+
         return $messageFactory
             ->createRequest('POST', $this->apiURL . $request->getPostURL())
             ->withHeader('Content-Type', 'multipart/form-data; boundary="' . $body->getBoundary() . '"')
@@ -96,8 +87,6 @@ private function makeMultipartFormDataRequest(GotenbergRequestInterface $request
     }
 
     /**
-     * @param ResponseInterface $response
-     * @return ResponseInterface
      * @throws ClientException
      */
     private function handleResponse(ResponseInterface $response): ResponseInterface
@@ -106,7 +95,7 @@ private function handleResponse(ResponseInterface $response): ResponseInterface
             case 200:
                 return $response;
             default:
-                throw new ClientException($response->getBody(), $response->getStatusCode());
+                throw new ClientException($response->getBody()->getContents(), $response->getStatusCode());
         }
     }
 }
diff --git a/src/ClientException.php b/src/ClientException.php
index 44a7bec..aee5edf 100644
--- a/src/ClientException.php
+++ b/src/ClientException.php
@@ -1,8 +1,11 @@
 <?php
 
+declare(strict_types=1);
+
 namespace TheCodingMachine\Gotenberg;
 
-final class ClientException extends \Exception
-{
+use Exception;
 
+final class ClientException extends Exception
+{
 }
diff --git a/src/Document.php b/src/Document.php
index aa4e280..5ce67f0 100644
--- a/src/Document.php
+++ b/src/Document.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace TheCodingMachine\Gotenberg;
 
 use Psr\Http\Message\StreamInterface;
@@ -12,28 +14,17 @@ final class Document
     /** @var StreamInterface */
     private $fileStream;
 
-    /**
-     * Document constructor.
-     * @param string $fileName
-     * @param StreamInterface $fileStream
-     */
     public function __construct(string $fileName, StreamInterface $fileStream)
     {
         $this->fileName = $fileName;
         $this->fileStream = $fileStream;
     }
 
-    /**
-     * @return string
-     */
     public function getFileName(): string
     {
         return $this->fileName;
     }
 
-    /**
-     * @return StreamInterface
-     */
     public function getFileStream(): StreamInterface
     {
         return $this->fileStream;
diff --git a/src/DocumentFactory.php b/src/DocumentFactory.php
index b78bfa6..85f99f0 100644
--- a/src/DocumentFactory.php
+++ b/src/DocumentFactory.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace TheCodingMachine\Gotenberg;
 
 use GuzzleHttp\Psr7\LazyOpenStream;
@@ -11,36 +13,24 @@
 
 final class DocumentFactory
 {
-    /**
-     * @param string $fileName
-     * @param string $filePath
-     * @return Document
-     */
     public static function makeFromPath(string $fileName, string $filePath): Document
     {
         return new Document($fileName, new LazyOpenStream($filePath, 'r'));
     }
 
-    /**
-     * @param string $fileName
-     * @param StreamInterface $fileStream
-     * @return Document
-     */
     public static function makeFromStream(string $fileName, StreamInterface $fileStream): Document
     {
         return new Document($fileName, $fileStream);
     }
 
     /**
-     * @param string $fileName
-     * @param string $string
-     * @return Document
      * @throws FilesystemException
      */
     public static function makeFromString(string $fileName, string $string): Document
     {
         $fileStream = fopen('php://memory', 'rb+');
         fwrite($fileStream, $string);
+
         return new Document($fileName, stream_for($fileStream));
     }
 }
diff --git a/src/GotenbergRequestInterface.php b/src/GotenbergRequestInterface.php
index 1ca3f60..9adea22 100644
--- a/src/GotenbergRequestInterface.php
+++ b/src/GotenbergRequestInterface.php
@@ -1,12 +1,11 @@
 <?php
 
+declare(strict_types=1);
+
 namespace TheCodingMachine\Gotenberg;
 
 interface GotenbergRequestInterface
 {
-    /**
-     * @return string
-     */
     public function getPostURL(): string;
 
     /**
diff --git a/src/HTMLRequest.php b/src/HTMLRequest.php
index f09e158..77dec84 100644
--- a/src/HTMLRequest.php
+++ b/src/HTMLRequest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace TheCodingMachine\Gotenberg;
 
 class HTMLRequest extends ChromeRequest implements GotenbergRequestInterface
@@ -10,19 +12,12 @@ class HTMLRequest extends ChromeRequest implements GotenbergRequestInterface
     /** @var Document[] */
     private $assets;
 
-    /**
-     * HTMLRequest constructor.
-     * @param Document $index
-     */
     public function __construct(Document $index)
     {
         $this->index = $index;
         $this->assets = [];
     }
 
-    /**
-     * @return string
-     */
     public function getPostURL(): string
     {
         return '/convert/html';
@@ -38,6 +33,7 @@ public function getFormFiles(): array
         foreach ($this->assets as $asset) {
             $files[$asset->getFileName()] = $asset;
         }
+
         return $files;
     }
 
diff --git a/src/MarkdownRequest.php b/src/MarkdownRequest.php
index 6b6f03d..4808978 100644
--- a/src/MarkdownRequest.php
+++ b/src/MarkdownRequest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace TheCodingMachine\Gotenberg;
 
 final class MarkdownRequest extends HTMLRequest implements GotenbergRequestInterface
@@ -8,8 +10,6 @@ final class MarkdownRequest extends HTMLRequest implements GotenbergRequestInter
     private $markdowns;
 
     /**
-     * MarkdownRequest constructor.
-     * @param Document $index
      * @param Document[] $markdowns
      */
     public function __construct(Document $index, array $markdowns)
@@ -18,9 +18,6 @@ public function __construct(Document $index, array $markdowns)
         $this->markdowns = $markdowns;
     }
 
-    /**
-     * @return string
-     */
     public function getPostURL(): string
     {
         return '/convert/markdown';
@@ -35,6 +32,7 @@ public function getFormFiles(): array
         foreach ($this->markdowns as $markdown) {
             $files[$markdown->getFileName()] = $markdown;
         }
+
         return $files;
     }
 }
diff --git a/src/MergeRequest.php b/src/MergeRequest.php
index 9a43f96..89e00a8 100644
--- a/src/MergeRequest.php
+++ b/src/MergeRequest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace TheCodingMachine\Gotenberg;
 
 final class MergeRequest extends Request implements GotenbergRequestInterface
@@ -8,7 +10,6 @@ final class MergeRequest extends Request implements GotenbergRequestInterface
     private $files;
 
     /**
-     * OfficeRequest constructor.
      * @param Document[] $files
      */
     public function __construct(array $files)
@@ -16,13 +17,9 @@ public function __construct(array $files)
         $this->files = $files;
     }
 
-
-    /**
-     * @return string
-     */
     public function getPostURL(): string
     {
-        return '/convert/merge';
+        return '/merge';
     }
 
     /**
@@ -34,6 +31,7 @@ public function getFormFiles(): array
         foreach ($this->files as $file) {
             $files[$file->getFileName()] = $file;
         }
+
         return $files;
     }
 }
diff --git a/src/OfficeRequest.php b/src/OfficeRequest.php
index 5a07d92..d319c73 100644
--- a/src/OfficeRequest.php
+++ b/src/OfficeRequest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace TheCodingMachine\Gotenberg;
 
 final class OfficeRequest extends Request implements GotenbergRequestInterface
@@ -13,7 +15,6 @@ final class OfficeRequest extends Request implements GotenbergRequestInterface
     private $landscape;
 
     /**
-     * OfficeRequest constructor.
      * @param Document[] $files
      */
     public function __construct(array $files)
@@ -21,9 +22,6 @@ public function __construct(array $files)
         $this->files = $files;
     }
 
-    /**
-     * @return string
-     */
     public function getPostURL(): string
     {
         return '/convert/office';
@@ -36,6 +34,7 @@ public function getFormValues(): array
     {
         $values = parent::getFormValues();
         $values[self::LANDSCAPE] = $this->landscape;
+
         return $values;
     }
 
@@ -48,12 +47,10 @@ public function getFormFiles(): array
         foreach ($this->files as $file) {
             $files[$file->getFileName()] = $file;
         }
+
         return $files;
     }
 
-    /**
-     * @param bool $landscape
-     */
     public function setLandscape(bool $landscape): void
     {
         $this->landscape = $landscape;
diff --git a/src/Request.php b/src/Request.php
index 3bae302..01031a3 100644
--- a/src/Request.php
+++ b/src/Request.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace TheCodingMachine\Gotenberg;
 
 abstract class Request
@@ -19,6 +21,7 @@ abstract class Request
     private const RESULT_FILENAME = 'resultFilename';
     private const WAIT_TIMEOUT = 'waitTimeout';
     private const WEBHOOK_URL = 'webhookURL';
+    private const WEBHOOK_URL_TIMEOUT = 'webhookURLTimeout';
 
     /** @var string|null */
     private $resultFilename;
@@ -29,45 +32,48 @@ abstract class Request
     /** @var string|null */
     private $webhookURL;
 
+    /** @var float|null */
+    private $webhookURLTimeout;
+
     /**
      * @return array<string,mixed>
      */
     public function getFormValues(): array
     {
         $values = [];
-        if (!empty($this->resultFilename)) {
+        if (! empty($this->resultFilename)) {
             $values[self::RESULT_FILENAME] = $this->resultFilename;
         }
-        if (!is_null($this->waitTimeout)) {
+        if ($this->waitTimeout !== null) {
             $values[self::WAIT_TIMEOUT] = $this->waitTimeout;
         }
-        if (!empty($this->webhookURL)) {
+        if (! empty($this->webhookURL)) {
             $values[self::WEBHOOK_URL] = $this->webhookURL;
         }
+        if (! empty($this->webhookURLTimeout)) {
+            $values[self::WEBHOOK_URL_TIMEOUT] = $this->webhookURLTimeout;
+        }
+
         return $values;
     }
 
-    /**
-     * @param string|null $resultFilename
-     */
     public function setResultFilename(?string $resultFilename): void
     {
         $this->resultFilename = $resultFilename;
     }
 
-    /**
-     * @param float|null $waitTimeout
-     */
     public function setWaitTimeout(?float $waitTimeout): void
     {
         $this->waitTimeout = $waitTimeout;
     }
 
-    /**
-     * @param string|null $webhookURL
-     */
     public function setWebhookURL(?string $webhookURL): void
     {
         $this->webhookURL = $webhookURL;
     }
+
+    public function setWebhookURLTimeout(?float $webhookURLTimeout): void
+    {
+        $this->webhookURLTimeout = $webhookURLTimeout;
+    }
 }
diff --git a/src/RequestException.php b/src/RequestException.php
index 964274b..b54f82b 100644
--- a/src/RequestException.php
+++ b/src/RequestException.php
@@ -1,8 +1,11 @@
 <?php
 
+declare(strict_types=1);
+
 namespace TheCodingMachine\Gotenberg;
 
-final class RequestException extends \Exception
-{
+use Exception;
 
+final class RequestException extends Exception
+{
 }
diff --git a/src/URLRequest.php b/src/URLRequest.php
index 262520f..fca96b6 100644
--- a/src/URLRequest.php
+++ b/src/URLRequest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace TheCodingMachine\Gotenberg;
 
 final class URLRequest extends ChromeRequest implements GotenbergRequestInterface
@@ -9,18 +11,11 @@ final class URLRequest extends ChromeRequest implements GotenbergRequestInterfac
     /** @var string */
     private $URL;
 
-    /**
-     * HTMLRequest constructor.
-     * @param string $URL
-     */
     public function __construct(string $URL)
     {
         $this->URL = $URL;
     }
 
-    /**
-     * @return string
-     */
     public function getPostURL(): string
     {
         return '/convert/url';
@@ -33,6 +28,7 @@ public function getFormValues(): array
     {
         $values = parent::getFormValues();
         $values[self::REMOTE_URL] = $this->URL;
+
         return $values;
     }
 }
diff --git a/tests/ClientTest.php b/tests/ClientTest.php
index 21aae94..a28a945 100644
--- a/tests/ClientTest.php
+++ b/tests/ClientTest.php
@@ -1,13 +1,16 @@
 <?php
 
+declare(strict_types=1);
+
 namespace TheCodingMachine\Gotenberg;
 
+use HTTP\Client\Exception;
 use PHPUnit\Framework\TestCase;
 use Safe\Exceptions\FilesystemException;
 
-class ClientTest extends TestCase
+final class ClientTest extends TestCase
 {
-    const API_URL = 'gotenberg:3000';
+    public const API_URL = 'gotenberg:3000';
 
     /** @var HTMLRequest */
     private $HTMLRequest;
@@ -27,7 +30,7 @@ class ClientTest extends TestCase
     /**
      * @throws RequestException
      */
-    public function setUp()
+    public function setUp(): void
     {
         $this->HTMLRequest = $this->createHTMLRequest();
         $this->URLRequest = $this->createURLRequest();
@@ -37,7 +40,6 @@ public function setUp()
     }
 
     /**
-     * @return HTMLRequest
      * @throws RequestException
      */
     private function createHTMLRequest(): HTMLRequest
@@ -52,18 +54,18 @@ private function createHTMLRequest(): HTMLRequest
         ];
         $request = new HTMLRequest($index);
         $request->setResultFilename('foo.pdf');
-        $request->setWaitTimeout(5);
-        $request->setWaitDelay(1);
+        $request->setWaitTimeout(5.0);
+        $request->setWaitDelay(1.0);
         $request->setHeader($header);
         $request->setFooter($footer);
         $request->setAssets($assets);
         $request->setPaperSize(Request::A4);
         $request->setMargins(Request::NO_MARGINS);
+
         return $request;
     }
 
     /**
-     * @return URLRequest
      * @throws RequestException
      */
     private function createURLRequest(): URLRequest
@@ -72,17 +74,17 @@ private function createURLRequest(): URLRequest
         $footer = DocumentFactory::makeFromPath('footer.html', __DIR__ . '/assets/url/footer.html');
         $request = new URLRequest('https://google.com');
         $request->setResultFilename('foo.pdf');
-        $request->setWaitTimeout(5);
-        $request->setWaitDelay(1);
+        $request->setWaitTimeout(5.0);
+        $request->setWaitDelay(1.0);
         $request->setHeader($header);
         $request->setFooter($footer);
         $request->setPaperSize(Request::A4);
         $request->setMargins(Request::NO_MARGINS);
+
         return $request;
     }
 
     /**
-     * @return MarkdownRequest
      * @throws RequestException
      */
     public function createMarkdownRequest(): MarkdownRequest
@@ -102,19 +104,17 @@ public function createMarkdownRequest(): MarkdownRequest
         ];
         $request = new MarkdownRequest($index, $markdowns);
         $request->setResultFilename('foo.pdf');
-        $request->setWaitTimeout(5);
-        $request->setWaitDelay(1);
+        $request->setWaitTimeout(5.0);
+        $request->setWaitDelay(1.0);
         $request->setHeader($header);
         $request->setFooter($footer);
         $request->setAssets($assets);
         $request->setPaperSize(Request::A4);
         $request->setMargins(Request::NO_MARGINS);
+
         return $request;
     }
 
-    /**
-     * @return OfficeRequest
-     */
     public function createOfficeRequest(): OfficeRequest
     {
         $files = [
@@ -122,14 +122,12 @@ public function createOfficeRequest(): OfficeRequest
         ];
         $request = new OfficeRequest($files);
         $request->setResultFilename('foo.pdf');
-        $request->setWaitTimeout(5);
+        $request->setWaitTimeout(5.0);
         $request->setLandscape(false);
+
         return $request;
     }
 
-    /**
-     * @return MergeRequest
-     */
     public function createMergeRequest(): MergeRequest
     {
         $files = [
@@ -138,15 +136,16 @@ public function createMergeRequest(): MergeRequest
         ];
         $request = new MergeRequest($files);
         $request->setResultFilename('foo.pdf');
-        $request->setWaitTimeout(5);
+        $request->setWaitTimeout(5.0);
+
         return $request;
     }
 
     /**
      * @throws ClientException
-     * @throws \HTTP\Client\Exception
+     * @throws Exception
      */
-    function testPost()
+    public function testPost(): void
     {
         $client = new Client(self::API_URL, new \Http\Adapter\Guzzle6\Client());
         // case 1: HTML.
@@ -174,9 +173,9 @@ function testPost()
     /**
      * @throws ClientException
      * @throws FilesystemException
-     * @throws \HTTP\Client\Exception
+     * @throws Exception
      */
-    function testStore()
+    public function testStore(): void
     {
         $client = new Client(self::API_URL);
         // case 1: HTML.
@@ -200,4 +199,4 @@ function testStore()
         $client->store($this->mergeRequest, $filePath);
         $this->assertFileExists($filePath);
     }
-}
\ No newline at end of file
+}
diff --git a/tests/DocumentFactoryTest.php b/tests/DocumentFactoryTest.php
index fddc342..69248c8 100644
--- a/tests/DocumentFactoryTest.php
+++ b/tests/DocumentFactoryTest.php
@@ -1,13 +1,15 @@
 <?php
 
+declare(strict_types=1);
+
 namespace TheCodingMachine\Gotenberg;
 
 use GuzzleHttp\Psr7\LazyOpenStream;
 use PHPUnit\Framework\TestCase;
 
-class DocumentFactoryTest extends TestCase
+final class DocumentFactoryTest extends TestCase
 {
-    function testMake()
+    public function testMake(): void
     {
         // case 1: uses a file path.
         $document = DocumentFactory::makeFromPath('file.pdf', __DIR__ . '/assets/file.pdf');
@@ -19,4 +21,4 @@ function testMake()
         $document = DocumentFactory::makeFromString('index.html', '<html>foo</html>');
         $this->assertNotEmpty($document->getFileStream());
     }
-}
\ No newline at end of file
+}