diff --git a/src/Error/ClientAware.php b/src/Error/ClientAware.php
index c347004..adccb0c 100644
--- a/src/Error/ClientAware.php
+++ b/src/Error/ClientAware.php
@@ -17,8 +17,9 @@ interface ClientAware
     /**
      * Returns true when exception message is safe to be displayed to a client.
      *
-     * @api
      * @return bool
+     *
+     * @api
      */
     public function isClientSafe();
 
@@ -27,8 +28,9 @@ interface ClientAware
      *
      * Value "graphql" is reserved for errors produced by query parsing or validation, do not use it.
      *
-     * @api
      * @return string
+     *
+     * @api
      */
     public function getCategory();
 }
diff --git a/src/Error/Error.php b/src/Error/Error.php
index 35019b2..8c3abb1 100644
--- a/src/Error/Error.php
+++ b/src/Error/Error.php
@@ -4,10 +4,13 @@ declare(strict_types=1);
 
 namespace GraphQL\Error;
 
+use Exception;
 use GraphQL\Language\AST\Node;
 use GraphQL\Language\Source;
 use GraphQL\Language\SourceLocation;
 use GraphQL\Utils\Utils;
+use JsonSerializable;
+use Throwable;
 use Traversable;
 use function array_filter;
 use function array_map;
@@ -28,7 +31,7 @@ use function iterator_to_array;
  * Class extends standard PHP `\Exception`, so all standard methods of base `\Exception` class
  * are available in addition to those listed below.
  */
-class Error extends \Exception implements \JsonSerializable, ClientAware
+class Error extends Exception implements JsonSerializable, ClientAware
 {
     const CATEGORY_GRAPHQL  = 'graphql';
     const CATEGORY_INTERNAL = 'internal';
@@ -85,7 +88,7 @@ class Error extends \Exception implements \JsonSerializable, ClientAware
      * @param Node|Node[]|Traversable|null $nodes
      * @param mixed[]|null                 $positions
      * @param mixed[]|null                 $path
-     * @param \Throwable                   $previous
+     * @param Throwable                    $previous
      * @param mixed[]                      $extensions
      */
     public function __construct(
@@ -100,7 +103,7 @@ class Error extends \Exception implements \JsonSerializable, ClientAware
         parent::__construct($message, 0, $previous);
 
         // Compute list of blame nodes.
-        if ($nodes instanceof \Traversable) {
+        if ($nodes instanceof Traversable) {
             $nodes = iterator_to_array($nodes);
         } elseif ($nodes && ! is_array($nodes)) {
             $nodes = [$nodes];
@@ -136,6 +139,7 @@ class Error extends \Exception implements \JsonSerializable, ClientAware
      * @param mixed        $error
      * @param Node[]|null  $nodes
      * @param mixed[]|null $path
+     *
      * @return Error
      */
     public static function createLocatedError($error, $nodes = null, $path = null)
@@ -159,7 +163,7 @@ class Error extends \Exception implements \JsonSerializable, ClientAware
             $source        = $error->source;
             $positions     = $error->positions;
             $extensions    = $error->extensions;
-        } elseif ($error instanceof \Exception || $error instanceof \Throwable) {
+        } elseif ($error instanceof Exception || $error instanceof Throwable) {
             $message       = $error->getMessage();
             $originalError = $error;
         } else {
@@ -222,7 +226,7 @@ class Error extends \Exception implements \JsonSerializable, ClientAware
     {
         if ($this->positions === null && ! empty($this->nodes)) {
             $positions = array_map(
-                function ($node) {
+                static function ($node) {
                     return isset($node->loc) ? $node->loc->start : null;
                 },
                 $this->nodes
@@ -230,7 +234,7 @@ class Error extends \Exception implements \JsonSerializable, ClientAware
 
             $this->positions = array_filter(
                 $positions,
-                function ($p) {
+                static function ($p) {
                     return $p !== null;
                 }
             );
@@ -250,8 +254,9 @@ class Error extends \Exception implements \JsonSerializable, ClientAware
      * point out to field mentioned in multiple fragments. Errors during execution include a
      * single location, the field which produced the error.
      *
-     * @api
      * @return SourceLocation[]
+     *
+     * @api
      */
     public function getLocations()
     {
@@ -262,7 +267,7 @@ class Error extends \Exception implements \JsonSerializable, ClientAware
 
             if ($positions && $source) {
                 $this->locations = array_map(
-                    function ($pos) use ($source) {
+                    static function ($pos) use ($source) {
                         return $source->getLocation($pos);
                     },
                     $positions
@@ -270,7 +275,7 @@ class Error extends \Exception implements \JsonSerializable, ClientAware
             } elseif ($nodes) {
                 $this->locations = array_filter(
                     array_map(
-                        function ($node) {
+                        static function ($node) {
                             if ($node->loc && $node->loc->source) {
                                 return $node->loc->source->getLocation($node->loc->start);
                             }
@@ -298,8 +303,9 @@ class Error extends \Exception implements \JsonSerializable, ClientAware
      * Returns an array describing the path from the root value to the field which produced this error.
      * Only included for execution errors.
      *
-     * @api
      * @return mixed[]|null
+     *
+     * @api
      */
     public function getPath()
     {
@@ -318,6 +324,7 @@ class Error extends \Exception implements \JsonSerializable, ClientAware
      * Returns array representation of error suitable for serialization
      *
      * @deprecated Use FormattedError::createFromException() instead
+     *
      * @return mixed[]
      */
     public function toSerializableArray()
@@ -328,7 +335,7 @@ class Error extends \Exception implements \JsonSerializable, ClientAware
 
         $locations = Utils::map(
             $this->getLocations(),
-            function (SourceLocation $loc) {
+            static function (SourceLocation $loc) {
                 return $loc->toSerializableArray();
             }
         );
@@ -348,7 +355,9 @@ class Error extends \Exception implements \JsonSerializable, ClientAware
 
     /**
      * Specify data which should be serialized to JSON
+     *
      * @link http://php.net/manual/en/jsonserializable.jsonserialize.php
+     *
      * @return mixed data which can be serialized by <b>json_encode</b>,
      * which is a value of any type other than a resource.
      */
diff --git a/src/Error/FormattedError.php b/src/Error/FormattedError.php
index 8ca886a..e03b2ac 100644
--- a/src/Error/FormattedError.php
+++ b/src/Error/FormattedError.php
@@ -4,12 +4,16 @@ declare(strict_types=1);
 
 namespace GraphQL\Error;
 
+use Countable;
+use ErrorException;
+use Exception;
 use GraphQL\Language\AST\Node;
 use GraphQL\Language\Source;
 use GraphQL\Language\SourceLocation;
 use GraphQL\Type\Definition\Type;
 use GraphQL\Type\Definition\WrappingType;
 use GraphQL\Utils\Utils;
+use Throwable;
 use function addcslashes;
 use function array_filter;
 use function array_intersect_key;
@@ -45,8 +49,9 @@ class FormattedError
      * Set default error message for internal errors formatted using createFormattedError().
      * This value can be overridden by passing 3rd argument to `createFormattedError()`.
      *
-     * @api
      * @param string $msg
+     *
+     * @api
      */
     public static function setInternalErrorMessage($msg)
     {
@@ -132,6 +137,7 @@ class FormattedError
 
     /**
      * @param int $len
+     *
      * @return string
      */
     private static function whitespace($len)
@@ -141,6 +147,7 @@ class FormattedError
 
     /**
      * @param int $len
+     *
      * @return string
      */
     private static function lpad($len, $str)
@@ -157,17 +164,20 @@ class FormattedError
      *
      * For a list of available debug flags see GraphQL\Error\Debug constants.
      *
-     * @api
-     * @param \Throwable $e
-     * @param bool|int   $debug
-     * @param string     $internalErrorMessage
+     * @param Throwable $e
+     * @param bool|int  $debug
+     * @param string    $internalErrorMessage
+     *
      * @return mixed[]
-     * @throws \Throwable
+     *
+     * @throws Throwable
+     *
+     * @api
      */
     public static function createFromException($e, $debug = false, $internalErrorMessage = null)
     {
         Utils::invariant(
-            $e instanceof \Exception || $e instanceof \Throwable,
+            $e instanceof Exception || $e instanceof Throwable,
             'Expected exception, got %s',
             Utils::getVariableType($e)
         );
@@ -189,7 +199,7 @@ class FormattedError
         if ($e instanceof Error) {
             $locations = Utils::map(
                 $e->getLocations(),
-                function (SourceLocation $loc) {
+                static function (SourceLocation $loc) {
                     return $loc->toSerializableArray();
                 }
             );
@@ -215,11 +225,13 @@ class FormattedError
      * Decorates spec-compliant $formattedError with debug entries according to $debug flags
      * (see GraphQL\Error\Debug for available flags)
      *
-     * @param mixed[]    $formattedError
-     * @param \Throwable $e
-     * @param bool       $debug
+     * @param mixed[]   $formattedError
+     * @param Throwable $e
+     * @param bool      $debug
+     *
      * @return mixed[]
-     * @throws \Throwable
+     *
+     * @throws Throwable
      */
     public static function addDebugEntries(array $formattedError, $e, $debug)
     {
@@ -228,7 +240,7 @@ class FormattedError
         }
 
         Utils::invariant(
-            $e instanceof \Exception || $e instanceof \Throwable,
+            $e instanceof Exception || $e instanceof Throwable,
             'Expected exception, got %s',
             Utils::getVariableType($e)
         );
@@ -259,7 +271,7 @@ class FormattedError
         }
 
         if ($debug & Debug::INCLUDE_TRACE) {
-            if ($e instanceof \ErrorException || $e instanceof \Error) {
+            if ($e instanceof ErrorException || $e instanceof \Error) {
                 $formattedError += [
                     'file' => $e->getFile(),
                     'line' => $e->getLine(),
@@ -282,15 +294,16 @@ class FormattedError
      * If initial formatter is not set, FormattedError::createFromException is used
      *
      * @param  bool $debug
-     * @return callable|\Closure
+     *
+     * @return callable|callable
      */
     public static function prepareFormatter(?callable $formatter = null, $debug)
     {
-        $formatter = $formatter ?: function ($e) {
+        $formatter = $formatter ?: static function ($e) {
             return FormattedError::createFromException($e);
         };
         if ($debug) {
-            $formatter = function ($e) use ($formatter, $debug) {
+            $formatter = static function ($e) use ($formatter, $debug) {
                 return FormattedError::addDebugEntries($formatter($e), $e, $debug);
             };
         }
@@ -301,9 +314,11 @@ class FormattedError
     /**
      * Returns error trace as serializable array
      *
-     * @api
-     * @param \Throwable $error
+     * @param Throwable $error
+     *
      * @return mixed[]
+     *
+     * @api
      */
     public static function toSafeTrace($error)
     {
@@ -319,12 +334,12 @@ class FormattedError
         }
 
         return array_map(
-            function ($err) {
+            static function ($err) {
                 $safeErr = array_intersect_key($err, ['file' => true, 'line' => true]);
 
                 if (isset($err['function'])) {
                     $func    = $err['function'];
-                    $args    = ! empty($err['args']) ? array_map([__CLASS__, 'printVar'], $err['args']) : [];
+                    $args    = ! empty($err['args']) ? array_map([self::class, 'printVar'], $err['args']) : [];
                     $funcStr = $func . '(' . implode(', ', $args) . ')';
 
                     if (isset($err['class'])) {
@@ -342,6 +357,7 @@ class FormattedError
 
     /**
      * @param mixed $var
+     *
      * @return string
      */
     public static function printVar($var)
@@ -356,7 +372,7 @@ class FormattedError
         }
 
         if (is_object($var)) {
-            return 'instance of ' . get_class($var) . ($var instanceof \Countable ? '(' . count($var) . ')' : '');
+            return 'instance of ' . get_class($var) . ($var instanceof Countable ? '(' . count($var) . ')' : '');
         }
         if (is_array($var)) {
             return 'array(' . count($var) . ')';
@@ -382,8 +398,10 @@ class FormattedError
 
     /**
      * @deprecated as of v0.8.0
+     *
      * @param string           $error
      * @param SourceLocation[] $locations
+     *
      * @return mixed[]
      */
     public static function create($error, array $locations = [])
@@ -392,7 +410,7 @@ class FormattedError
 
         if (! empty($locations)) {
             $formatted['locations'] = array_map(
-                function ($loc) {
+                static function ($loc) {
                     return $loc->toArray();
                 },
                 $locations
@@ -404,9 +422,10 @@ class FormattedError
 
     /**
      * @deprecated as of v0.10.0, use general purpose method createFromException() instead
+     *
      * @return mixed[]
      */
-    public static function createFromPHPError(\ErrorException $e)
+    public static function createFromPHPError(ErrorException $e)
     {
         return [
             'message'  => $e->getMessage(),
diff --git a/src/Error/InvariantViolation.php b/src/Error/InvariantViolation.php
index f108109..6f9cfad 100644
--- a/src/Error/InvariantViolation.php
+++ b/src/Error/InvariantViolation.php
@@ -4,6 +4,8 @@ declare(strict_types=1);
 
 namespace GraphQL\Error;
 
+use LogicException;
+
 /**
  * Class InvariantVoilation
  *
@@ -11,6 +13,6 @@ namespace GraphQL\Error;
  * This exception should not inherit base Error exception as it is raised when there is an error somewhere in
  * user-land code
  */
-class InvariantViolation extends \LogicException
+class InvariantViolation extends LogicException
 {
 }
diff --git a/src/Error/UserError.php b/src/Error/UserError.php
index a04ed78..67bb9bb 100644
--- a/src/Error/UserError.php
+++ b/src/Error/UserError.php
@@ -4,12 +4,14 @@ declare(strict_types=1);
 
 namespace GraphQL\Error;
 
+use RuntimeException;
+
 /**
  * Class UserError
  *
  * Error caused by actions of GraphQL clients. Can be safely displayed to a client...
  */
-class UserError extends \RuntimeException implements ClientAware
+class UserError extends RuntimeException implements ClientAware
 {
     /**
      * @return bool
diff --git a/src/Error/Warning.php b/src/Error/Warning.php
index 16add8b..a652968 100644
--- a/src/Error/Warning.php
+++ b/src/Error/Warning.php
@@ -50,8 +50,9 @@ final class Warning
      *
      * When passing true - suppresses all warnings.
      *
-     * @api
      * @param bool|int $suppress
+     *
+     * @api
      */
     public static function suppress($suppress = true)
     {
@@ -74,8 +75,9 @@ final class Warning
      *
      * When passing true - re-enables all warnings.
      *
-     * @api
      * @param bool|int $enable
+     *
+     * @api
      */
     public static function enable($enable = true)
     {