diff --git a/.gitattributes b/.gitattributes
index 4a24ebf..c8442fa 100644
--- a/.gitattributes
+++ b/.gitattributes
@@ -1,5 +1,6 @@
 /.gitattributes     export-ignore
 /.gitignore         export-ignore
+/.phpcs.xml.dist    export-ignore
 /box.json           export-ignore
 /.github            export-ignore
 /tests              export-ignore
diff --git a/.github/workflows/qa.yml b/.github/workflows/qa.yml
index 3c26aa8..981e2eb 100644
--- a/.github/workflows/qa.yml
+++ b/.github/workflows/qa.yml
@@ -35,3 +35,33 @@ jobs:
         uses: docker://rhysd/actionlint:latest
         with:
           args: -color
+
+  phpcs:
+    name: 'PHPCS'
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
+        with:
+          persist-credentials: false
+
+      - name: Install PHP
+        uses: shivammathur/setup-php@accd6127cb78bee3e8082180cb391013d204ef9f # 2.37.0
+        with:
+          php-version: 'latest'
+          coverage: none
+          tools: cs2pr
+
+      # Install dependencies and handle caching in one go.
+      # @link https://github.com/marketplace/actions/install-composer-dependencies
+      - name: Install Composer dependencies
+        uses: "ramsey/composer-install@65e4f84970763564f46a70b8a54b90d033b3bdda" # 4.0.0
+
+      # Check the code-style consistency of the PHP files.
+      - name: Check PHP code style
+        continue-on-error: true
+        run: composer checkcs -- --report-full --report-checkstyle=./phpcs-report.xml
+
+      - name: Show PHPCS results in PR
+        run: cs2pr ./phpcs-report.xml
diff --git a/.gitignore b/.gitignore
index 5c319eb..82e3acb 100644
--- a/.gitignore
+++ b/.gitignore
@@ -3,6 +3,8 @@ tests/cache
 vendor/
 composer.phar
 .DS_Store
+.phpcs.xml
+phpcs.xml
 
 # Ignore PhpStorm project related files.
 .idea
diff --git a/.phpcs.xml.dist b/.phpcs.xml.dist
new file mode 100644
index 0000000..d1d7929
--- /dev/null
+++ b/.phpcs.xml.dist
@@ -0,0 +1,99 @@
+<?xml version="1.0"?>
+<ruleset xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+    name="Patchwork"
+    xsi:noNamespaceSchemaLocation="./vendor/squizlabs/php_codesniffer/phpcs.xsd">
+
+    <description>Patchwork rules for PHP_CodeSniffer</description>
+
+    <!--
+    #############################################################################
+    COMMAND LINE ARGUMENTS
+    https://github.com/PHPCSStandards/PHP_CodeSniffer/wiki/Annotated-Ruleset
+    #############################################################################
+    -->
+
+    <!-- Scan all files. -->
+    <file>.</file>
+
+    <!-- Third party files and build files don't need to comply with these coding standards. -->
+    <exclude-pattern>*/vendor/*</exclude-pattern>
+
+    <!-- Test fixtures don't need to comply with these coding standards
+         as we may be specifically testing a variation in how syntax can be written.
+    -->
+    <exclude-pattern>*/tests/includes/*</exclude-pattern>
+
+    <!-- Only check PHP files.
+         Note: at this time PHPCS can not scan .phpt files.
+         There is a feature request open to change this.
+         https://github.com/PHPCSStandards/PHP_CodeSniffer/issues/1363
+    -->
+    <arg name="extensions" value="php"/>
+
+    <!-- Show progress, show the error codes for each message (source). -->
+    <arg value="ps"/>
+
+    <!-- Strip the filepaths down to the relevant bit. -->
+    <arg name="basepath" value="./"/>
+
+    <!-- Check up to 8 files simultaneously. -->
+    <arg name="parallel" value="8"/>
+
+
+    <!--
+    #############################################################################
+    CHECK FOR PHP CROSS-VERSION COMPATIBILITY
+    #############################################################################
+    -->
+
+    <config name="testVersion" value="7.1-"/>
+    <rule ref="PHPCompatibility"/>
+
+
+    <!--
+    #############################################################################
+    FOLLOW PSR12 for CODING STYLE
+    #############################################################################
+    -->
+
+    <rule ref="PSR12">
+        <!-- Re-organising the files should be a separate consideration and needs discussion
+             about whether or not to adopt PSR-4 or another convention.
+        -->
+        <exclude name="PSR1.Files.SideEffects"/>
+        <exclude name="PSR1.Classes.ClassDeclaration.MultipleClasses"/>
+    </rule>
+
+
+    <!--
+    #############################################################################
+    SNIFF SPECIFIC CONFIGURATION
+    #############################################################################
+    -->
+
+    <!-- Allow for slightly longer line length than PSR12 (120) allows for. -->
+    <rule ref="Generic.Files.LineLength">
+        <properties>
+            <property name="lineLimit" value="140" />
+        </properties>
+    </rule>
+
+
+    <!--
+    #############################################################################
+    SELECTIVE EXCLUSIONS
+    Exclude specific files for specific sniffs.
+    #############################################################################
+    -->
+
+    <!-- Renaming these methods from snake_case to camelCaps would be a BC-break. -->
+    <rule ref="PSR1.Methods.CamelCapsMethodName.NotCamelCaps">
+        <exclude-pattern>/src/CodeManipulation/Stream\.php$</exclude-pattern>
+    </rule>
+
+    <!-- Renaming these constants from camelCaps to ALL_CAPPS would be a BC-break. -->
+    <rule ref="Generic.NamingConventions.UpperCaseConstantName.ClassConstantNotUpperCase">
+        <exclude-pattern>/src/CodeManipulation/Actions/RedefinitionOfNew\.php$</exclude-pattern>
+    </rule>
+
+</ruleset>
diff --git a/composer.json b/composer.json
index f41c39e..25ecb1c 100644
--- a/composer.json
+++ b/composer.json
@@ -10,14 +10,40 @@
             "email": "ignas.rudaitis@gmail.com"
         }
     ],
-    "minimum-stability": "stable",
     "require": {
         "php": ">=7.1.0"
     },
     "require-dev": {
-        "phpunit/phpunit": ">=4"
+        "phpcompatibility/php-compatibility": "^10.0.0@alpha",
+        "phpunit/phpunit": ">=4",
+        "squizlabs/php_codesniffer": "^3.13.5 || ^4.0"
     },
+    "minimum-stability": "alpha",
+    "prefer-stable": true,
     "config": {
+        "allow-plugins": {
+            "dealerdirect/phpcodesniffer-composer-installer": true
+        },
         "lock": false
+    },
+    "scripts": {
+        "checkcs": [
+            "@php ./vendor/squizlabs/php_codesniffer/bin/phpcs"
+        ],
+        "fixcs": [
+            "@php ./vendor/squizlabs/php_codesniffer/bin/phpcbf"
+        ],
+        "test": [
+            "@php ./vendor/phpunit/phpunit/phpunit --no-coverage"
+        ],
+        "coverage": [
+            "@php ./vendor/phpunit/phpunit/phpunit"
+        ]
+    },
+    "scripts-descriptions": {
+        "checkcs": "Check the PHP files for code style violations and best practices.",
+        "fixcs": "Auto-fix code style violations in the PHP files.",
+        "test": "Run the unit tests without code coverage.",
+        "coverage": "Run the unit tests with code coverage."
     }
 }
diff --git a/src/CallRerouting.php b/src/CallRerouting.php
index 121329a..50fc557 100644
--- a/src/CallRerouting.php
+++ b/src/CallRerouting.php
@@ -360,6 +360,7 @@ function connectOnHHVM($function, Handle $handle)
         } elseif (is_object($obj)) {
             $calledClass = get_class($obj);
         }
+        // phpcs:ignore PHPCompatibility.FunctionUse.ArgumentFunctionsReportCurrentValue.NeedsInspection -- Verified okay.
         $frame = count(debug_backtrace(0)) - 1;
         $result = null;
         $done = dispatch($class, $calledClass, $method, $frame, $result, $args);
diff --git a/src/CodeManipulation/Actions/Namespaces.php b/src/CodeManipulation/Actions/Namespaces.php
index edc2e67..41968ac 100644
--- a/src/CodeManipulation/Actions/Namespaces.php
+++ b/src/CodeManipulation/Actions/Namespaces.php
@@ -52,6 +52,7 @@ function getNamespaceAt(Source $s, $pos)
 
 function collectNamespaceBoundaries(Source $s)
 {
+    // phpcs:disable PHPCompatibility.FunctionDeclarations.NewClosure.ThisFoundOutsideClass -- Using $this is okay. Source::cache() binds the closure.
     return $s->cache([], function () {
         if (!$this->has(T_NAMESPACE)) {
             return ['' => [[0, INF]]];
@@ -71,6 +72,7 @@ function collectNamespaceBoundaries(Source $s)
         }
         return $result;
     });
+    // phpcs:enable
 }
 
 function collectUseDeclarations(Source $s, $begin)
@@ -84,6 +86,8 @@ function collectUseDeclarations(Source $s, $begin)
             }
         }
     }
+
+    // phpcs:disable PHPCompatibility.FunctionDeclarations.NewClosure.ThisFoundOutsideClass -- Using $this is okay. Source::cache() binds the closure.
     return $s->cache([$begin], function ($begin) {
         $result = ['class' => [], 'function' => [], 'const' => []];
         # only tokens that are siblings bracket-wise are considered,
@@ -98,6 +102,7 @@ function collectUseDeclarations(Source $s, $begin)
         }
         return $result;
     });
+    // phpcs:enable
 }
 
 function parseUseDeclaration(Source $s, $pos, array &$aliases, $prefix = '', $type = 'class')
diff --git a/src/CodeManipulation/Actions/RedefinitionOfNew.php b/src/CodeManipulation/Actions/RedefinitionOfNew.php
index 304b98e..4629bf4 100644
--- a/src/CodeManipulation/Actions/RedefinitionOfNew.php
+++ b/src/CodeManipulation/Actions/RedefinitionOfNew.php
@@ -16,6 +16,7 @@
 
 const STATIC_INSTANTIATION_REPLACEMENT = '\Patchwork\CallRerouting\getInstantiator(\'%s\', %s)->instantiate(%s)';
 const DYNAMIC_INSTANTIATION_REPLACEMENT = '\Patchwork\CallRerouting\getInstantiator(%s, %s)->instantiate(%s)';
+// phpcs:ignore Generic.Files.LineLength.TooLong
 const CALLED_CLASS = '((__CLASS__ && __FUNCTION__ !== (__NAMESPACE__ ? __NAMESPACE__ . "\\\\{closure}" : "\\\\{closure}")) ? \get_called_class() : null)';
 
 const spliceAllInstantiations = 'Patchwork\CodeManipulation\Actions\RedefinitionOfNew\spliceAllInstantiations';