diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 87eacf1..e9683dc 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -17,5 +17,8 @@ jobs:
     - name: Install dependencies
       run: composer install --prefer-dist --no-progress --no-suggest
 
-    - name: PHPStan
-      run: vendor/bin/phpstan analyze
+    - name: Install Psalm
+      run: composer require --dev vimeo/psalm:dev-master@dev --no-suggest
+
+    - name: Psalm
+      run: vendor/bin/psalm --output-format=github --shepherd
diff --git a/README.md b/README.md
index defbfb2..3370fc4 100644
--- a/README.md
+++ b/README.md
@@ -92,3 +92,7 @@ features and integration tests. Special thanks goes to
 [@lunika](https://github.com/lunika), [@rgazelot](https://github.com/rgazelot)
 and [@krichprollsch](https://github.com/krichprollsch), who helped conceived
 this extension, and also pushed me to open-source it.
+
+Badges
+------
+![Psalm Shepherd](https://shepherd.dev/github/Taluu/Behapi/coverage.svg)
diff --git a/composer.json b/composer.json
index 666de43..e1d1388 100644
--- a/composer.json
+++ b/composer.json
@@ -62,8 +62,6 @@
         "symfony/http-client": "^4.3 || ^5.0",
         "symfony/var-dumper": "^2.8 || ^3.3 || ^4.0",
 
-        "phpstan/phpstan": "^0.10",
-        "phpstan/phpstan-strict-rules": "^0.10",
-        "phpstan/phpstan-beberlei-assert": "^0.10"
+        "vimeo/psalm": "^3.8"
     }
 }
diff --git a/phpstan.neon b/phpstan.neon
deleted file mode 100644
index 87e21fa..0000000
--- a/phpstan.neon
+++ /dev/null
@@ -1,19 +0,0 @@
-parameters:
-  level: max
-  paths:
-    - src
-
-  ignoreErrors:
-    # have to ignore it, because Symfony config works like that and I'm waaay
-    # too lazy to properly structure the node builders just to add some asserts
-    # and stuff like that for (almost) every line.
-    - '{^Cannot call method arrayNode\\() on Symfony\Component\Config\Definition\Builder\NodeParentInterface|null.$}'
-
-    # have to ignore it until php 7.4, which introduces (co)vrariance on arguments
-    # and return hint, as beberlei/assert introduced a tiny bc break making it
-    # impossible to properly extend its classes until php 7.4
-    - '{^Call to an undefined method Assert\\AssertionChain::not().}'
-
-  includes:
-    - vendor/phpstan/phpstan-strict-rules/rules.neon
-    - vendor/phpstan/phpstan-beberlei-assert/extension.neon
diff --git a/psalm.xml b/psalm.xml
new file mode 100644
index 0000000..e2cedae
--- /dev/null
+++ b/psalm.xml
@@ -0,0 +1,19 @@
+<?xml version="1.0"?>
+<psalm
+    totallyTyped="false"
+    resolveFromConfigFile="true"
+    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+    xmlns="https://getpsalm.org/schema/config"
+    xsi:schemaLocation="https://getpsalm.org/schema/config vendor/vimeo/psalm/config.xsd"
+>
+    <projectFiles>
+        <directory name="src" />
+        <ignoreFiles>
+            <directory name="vendor" />
+        </ignoreFiles>
+    </projectFiles>
+
+    <issueHandlers>
+        <LessSpecificReturnType errorLevel="info" />
+    </issueHandlers>
+</psalm>
diff --git a/src/Assert/Assertion.php b/src/Assert/Assertion.php
index 4ded19b..05a2318 100644
--- a/src/Assert/Assertion.php
+++ b/src/Assert/Assertion.php
@@ -15,8 +15,12 @@
  */
 abstract class Assertion extends Beberlei\Assertion
 {
-    /** @return bool */
-    public static function empty($value, $message = null, ?string $propertyPath = null): bool
+    /**
+     * @param mixed $value
+     * @param string|null $message
+     * @return bool
+     */
+    public static function empty($value, ?string $message = null, ?string $propertyPath = null): bool
     {
         return parent::noContent($value, $message, $propertyPath);
     }
diff --git a/src/Behapi.php b/src/Behapi.php
index 0c515df..bd811d0 100644
--- a/src/Behapi.php
+++ b/src/Behapi.php
@@ -24,14 +24,16 @@ final class Behapi implements Extension
 {
     const DEBUG_INTROSPECTION_TAG = 'behapi.debug.introspection';
 
-    /** {@inheritDoc} */
-    public function getConfigKey()
+    public function getConfigKey(): string
     {
         return 'behapi';
     }
 
-    /** {@inheritDoc} */
-    public function configure(ArrayNodeDefinition $builder)
+    /**
+     * @psalm-suppress PossiblyUndefinedMethod
+     * @psalm-suppress PossiblyNullReference
+     */
+    public function configure(ArrayNodeDefinition $builder): void
     {
         $builder
             ->children()
@@ -89,13 +91,11 @@ public function configure(ArrayNodeDefinition $builder)
 
     }
 
-    /** {@inheritDoc} */
-    public function initialize(ExtensionManager $extensionManager)
+    public function initialize(ExtensionManager $extensionManager): void
     {
     }
 
-    /** {@inheritDoc} */
-    public function load(ContainerBuilder $container, array $config)
+    public function load(ContainerBuilder $container, array $config): void
     {
         $container->register(HttpHistory\History::class, HttpHistory\History::class)
             ->setPublic(false)
@@ -112,8 +112,7 @@ public function load(ContainerBuilder $container, array $config)
         $this->loadContainer($container, $config);
     }
 
-    /** {@inheritDoc} */
-    public function process(ContainerBuilder $container)
+    public function process(ContainerBuilder $container): void
     {
         $dumpers = [];
 
diff --git a/src/Container.php b/src/Container.php
index 8aa7b42..fea61c7 100644
--- a/src/Container.php
+++ b/src/Container.php
@@ -72,12 +72,13 @@ private function getPluginClientBuilder(): PluginClientBuilder
         $uriFactory = Psr17FactoryDiscovery::findUrlFactory();
 
         $baseUri = $uriFactory->createUri($this->baseUrl);
+        $httpHistory = $this->services[HttpHistory::class];
 
-        assert($this->services[HttpHistory::class] instanceof HttpHistory);
+        assert($httpHistory instanceof HttpHistory);
 
         $builder = $builder->addPlugin(new ContentLengthPlugin);
         $builder = $builder->addPlugin(new BaseUriPlugin($baseUri));
-        $builder = $builder->addPlugin(new HistoryPlugin($this->services[HttpHistory::class]));
+        $builder = $builder->addPlugin(new HistoryPlugin($httpHistory));
 
         return $builder;
     }
diff --git a/src/Debug/CliController.php b/src/Debug/CliController.php
index 911b3f8..d24576f 100644
--- a/src/Debug/CliController.php
+++ b/src/Debug/CliController.php
@@ -19,19 +19,19 @@ public function __construct(Status $status)
         $this->status = $status;
     }
 
-    /** {@inheritDoc} */
-    public function configure(Command $command)
+    public function configure(Command $command): void
     {
         $command
             ->addOption('behapi-debug', null, InputOption::VALUE_NONE, 'Activates the debug mode for behapi');
     }
 
-    /** {@inheritDoc} */
     public function execute(InputInterface $input, OutputInterface $output)
     {
         $debug = $input->getOption('behapi-debug');
         assert(is_bool($debug));
 
         $this->status->setEnabled($debug);
+
+        return null;
     }
 }
diff --git a/src/Debug/Listener.php b/src/Debug/Listener.php
index 7463050..28df9de 100644
--- a/src/Debug/Listener.php
+++ b/src/Debug/Listener.php
@@ -48,8 +48,7 @@ public function __construct(Status $status, HttpHistory $history, array $adapter
         $this->status = $status;
     }
 
-    /** {@inheritDoc} */
-    public static function getSubscribedEvents()
+    public static function getSubscribedEvents(): array
     {
         return [
             ExampleTested::AFTER => 'debugAfter',
@@ -101,6 +100,11 @@ private function debug(MessageInterface $message): void
         }
     }
 
+    /**
+     * @psalm-suppress InvalidReturnType
+     * @psalm-suppress InvalidReturnStatement
+     * @psalm-suppress UndefinedDocblockClass
+     */
     private function hasTag(ScenarioLikeTested $event, string $tag): bool
     {
         $node = $event->getNode();
diff --git a/src/Debug/Status.php b/src/Debug/Status.php
index 6a768bf..89432a0 100644
--- a/src/Debug/Status.php
+++ b/src/Debug/Status.php
@@ -11,7 +11,7 @@ final class Status
     /** @var bool */
     private $enabled = false;
 
-    public function setEnabled(bool $enabled)
+    public function setEnabled(bool $enabled): void
     {
         $this->enabled = $enabled;
     }
diff --git a/src/HttpHistory/History.php b/src/HttpHistory/History.php
index ea79b7f..bbf0cce 100644
--- a/src/HttpHistory/History.php
+++ b/src/HttpHistory/History.php
@@ -53,6 +53,7 @@ public function getLastResponse(): ResponseInterface
         return $response;
     }
 
+    /** @return Generator<int, Tuple, mixed, int> */
     public function getTuples(): Generator
     {
         yield from $this->tuples;
diff --git a/src/HttpHistory/Listener.php b/src/HttpHistory/Listener.php
index c941e9a..6af7b95 100644
--- a/src/HttpHistory/Listener.php
+++ b/src/HttpHistory/Listener.php
@@ -22,8 +22,7 @@ public function __construct(History $history)
         $this->history = $history;
     }
 
-    /** {@inheritDoc} */
-    public static function getSubscribedEvents()
+    public static function getSubscribedEvents(): array
     {
         return [
             ExampleTested::AFTER => ['clear', -99],
diff --git a/src/Json/Context.php b/src/Json/Context.php
index a08e9e4..7852ca7 100644
--- a/src/Json/Context.php
+++ b/src/Json/Context.php
@@ -13,6 +13,7 @@
 use Symfony\Component\PropertyAccess\PropertyAccessor;
 
 use Behapi\Assert\Assert;
+use Behapi\Assert\AssertionChain;
 use Behapi\HttpHistory\History as HttpHistory;
 
 use function sprintf;
@@ -32,12 +33,13 @@ class Context implements BehatContext
     /** @var HttpHistory */
     private $history;
 
-    /** @var string[] */
+    /** @var list<string> */
     private $contentTypes;
 
     /** @var PropertyAccessor */
     private $accessor;
 
+    /** @param list<string> $contentTypes */
     public function __construct(HttpHistory $history, array $contentTypes = ['application/json'])
     {
         $this->accessor = PropertyAccess::createPropertyAccessor();
@@ -63,6 +65,7 @@ final public function path_should_be_readable(string $path, ?string $not = null)
         $assert = Assert::that($this->accessor->isReadable($this->getValue(null), $path));
 
         if ($not !== null) {
+            assert($assert instanceof AssertionChain);
             $assert = $assert->not();
         }
 
@@ -70,6 +73,8 @@ final public function path_should_be_readable(string $path, ?string $not = null)
     }
 
     /**
+     * @param mixed $expected
+     *
      * @Then in the json, :path should be equal to :expected
      * @Then in the json, :path should :not be equal to :expected
      */
@@ -78,6 +83,7 @@ final public function the_json_path_should_be_equal_to(string $path, ?string $no
         $assert = Assert::that($this->getValue($path));
 
         if ($not !== null) {
+            assert($assert instanceof AssertionChain);
             $assert = $assert->not();
         }
 
@@ -93,6 +99,7 @@ final public function the_json_path_should_be_py_string(string $path, ?string $n
         $assert = Assert::that($this->getValue($path));
 
         if ($not !== null) {
+            assert($assert instanceof AssertionChain);
             $assert = $assert->not();
         }
 
@@ -108,6 +115,7 @@ final public function the_json_path_should_be(string $path, ?string $not = null,
         $assert = Assert::that($this->getValue($path));
 
         if ($not !== null) {
+            assert($assert instanceof AssertionChain);
             $assert = $assert->not();
         }
 
@@ -123,6 +131,7 @@ final public function the_json_path_should_be_null(string $path, ?string $not =
         $assert = Assert::that($this->getValue($path));
 
         if ($not !== null) {
+            assert($assert instanceof AssertionChain);
             $assert = $assert->not();
         }
 
@@ -136,6 +145,7 @@ final public function the_json_path_should_be_null(string $path, ?string $not =
     final public function the_json_path_should_be_empty(string $path, ?string $not = null): void
     {
         $assert = Assert::that($this->getValue($path));
+        assert($assert instanceof AssertionChain);
 
         if ($not !== null) {
             $assert = $assert->not();
@@ -145,6 +155,8 @@ final public function the_json_path_should_be_empty(string $path, ?string $not =
     }
 
     /**
+     * @param mixed $expected
+     *
      * @Then in the json, :path should contain :expected
      * @Then in the json, :path should :not contain :expected
      */
@@ -153,13 +165,18 @@ final public function the_json_path_contains(string $path, ?string $not = null,
         $assert = Assert::that($this->getValue($path));
 
         if ($not !== null) {
+            assert($assert instanceof AssertionChain);
             $assert = $assert->not();
         }
 
         $assert->contains($expected);
     }
 
-    /** @Then in the json, :path collection should contain an element with :value equal to :expected */
+    /**
+     * @param mixed $expected
+     *
+     * @Then in the json, :path collection should contain an element with :value equal to :expected
+     */
     final public function the_json_path_collection_contains(string $path, string $value, $expected): void
     {
         $collection = $this->getValue($path);
@@ -215,7 +232,7 @@ final public function the_json_path_should_be_a_valid_json_encoded_string(string
      * overwrite it if you want to add supplementary checks or use something
      * else instead (such as Seldaek's JsonLint package).
      */
-    public function response_should_be_a_valid_json_response()
+    public function response_should_be_a_valid_json_response(): void
     {
         $this->getValue(null);
 
@@ -239,6 +256,7 @@ final public function the_json_path_should_match(string $path, ?string $not = nu
         $assert = Assert::that($this->getValue($path));
 
         if ($not !== null) {
+            assert($assert instanceof AssertionChain);
             $assert = $assert->not();
         }
 
diff --git a/src/Json/EachInCollectionTrait.php b/src/Json/EachInCollectionTrait.php
index ccdce6a..f679727 100644
--- a/src/Json/EachInCollectionTrait.php
+++ b/src/Json/EachInCollectionTrait.php
@@ -4,6 +4,7 @@
 use Symfony\Component\PropertyAccess\PropertyAccessor;
 
 use Behapi\Assert\Assert;
+use Behapi\Assert\AssertionChain;
 
 trait EachInCollectionTrait
 {
@@ -21,6 +22,7 @@ final public function the_json_path_elements_in_collection_should_have_a_propert
         $assert = Assert::that($this->getValue(empty($path) ? null : $path));
 
         if ($not !== null) {
+            assert($assert instanceof AssertionChain);
             $assert = $assert->not();
         }
 
@@ -42,13 +44,23 @@ final public function the_json_each_elements_in_collection_should_be_equal_to(st
             ->isTraversable()
         ;
 
-        $values = array_map(function ($value) use ($property) { return $this->accessor->getValue($value, $property); }, $values);
+        $values = array_map(
+            /**
+             * @param mixed $value
+             * @return mixed
+             */
+            function ($value) use ($property) {
+                return $this->accessor->getValue($value, $property);
+            },
+            $values
+        );
 
         $assert = Assert::that($values)
             ->all()
         ;
 
         if ($not !== null) {
+            assert($assert instanceof AssertionChain);
             $assert = $assert->not();
         }
 
@@ -67,7 +79,16 @@ final public function the_json_each_elements_in_collection_should_be_bool(string
             ->isTraversable()
         ;
 
-        $values = array_map(function ($value) use ($property) { return $this->accessor->getValue($value, $property); }, $values);
+        $values = array_map(
+            /**
+             * @param mixed $value
+             * @return mixed
+             */
+            function ($value) use ($property) {
+                return $this->accessor->getValue($value, $property);
+            },
+            $values
+        );
 
         $assert = Assert::that($values)
             ->all()
@@ -75,6 +96,7 @@ final public function the_json_each_elements_in_collection_should_be_bool(string
         ;
 
         if ($not !== null) {
+            assert($assert instanceof AssertionChain);
             $assert = $assert->not();
         }
 
@@ -93,7 +115,16 @@ final public function the_json_each_elements_in_collection_should_be_equal_to_in
             ->isTraversable()
         ;
 
-        $values = array_map(function ($value) use ($property) { return $this->accessor->getValue($value, $property); }, $values);
+        $values = array_map(
+            /**
+             * @param mixed $value
+             * @return mixed
+             */
+            function ($value) use ($property) {
+                return $this->accessor->getValue($value, $property);
+            },
+            $values
+        );
 
         $assert = Assert::that($values)
             ->all()
@@ -101,6 +132,7 @@ final public function the_json_each_elements_in_collection_should_be_equal_to_in
         ;
 
         if ($not !== null) {
+            assert($assert instanceof AssertionChain);
             $assert = $assert->not();
         }
 
@@ -119,13 +151,23 @@ final public function the_json_each_elements_in_collection_should_contain(string
             ->isTraversable()
         ;
 
-        $values = array_map(function ($value) use ($property) { return $this->accessor->getValue($value, $property); }, $values);
+        $values = array_map(
+            /**
+             * @param mixed $value
+             * @return mixed
+             */
+            function ($value) use ($property) {
+                return $this->accessor->getValue($value, $property);
+            },
+            $values
+        );
 
         $assert = Assert::that($values)
             ->all()
         ;
 
         if ($not !== null) {
+            assert($assert instanceof AssertionChain);
             $assert = $assert->not();
         }
 
diff --git a/src/PhpMatcher/JsonContext.php b/src/PhpMatcher/JsonContext.php
index dfcafc8..a1fd4fb 100644
--- a/src/PhpMatcher/JsonContext.php
+++ b/src/PhpMatcher/JsonContext.php
@@ -1,20 +1,15 @@
 <?php declare(strict_types=1);
 namespace Behapi\PhpMatcher;
 
-use stdClass;
 use InvalidArgumentException;
 
 use Behat\Behat\Context\Context;
 use Behat\Gherkin\Node\PyStringNode;
 
-use Symfony\Component\PropertyAccess\PropertyAccess;
-use Symfony\Component\PropertyAccess\PropertyAccessor;
-
 use Behapi\HttpHistory\History as HttpHistory;
 
 use function sprintf;
-use function json_encode;
-use function json_decode;
+use function is_string;
 
 class JsonContext implements Context
 {
@@ -24,14 +19,10 @@ class JsonContext implements Context
     /** @var MatcherFactory */
     private $factory;
 
-    /** @var PropertyAccessor */
-    private $accessor;
-
     public function __construct(HttpHistory $history)
     {
         $this->history = $history;
         $this->factory = new MatcherFactory;
-        $this->accessor = PropertyAccess::createPropertyAccessor();
     }
 
     /** @Then the root should match: */
@@ -39,73 +30,18 @@ final public function root_should_match(PyStringNode $pattern): void
     {
         $matcher = $this->factory->createMatcher();
 
-        if ($matcher->match($this->getJson(), $pattern->getRaw())) {
+        if ($matcher->match((string) $this->history->getLastResponse()->getBody(), $pattern->getRaw())) {
             return;
         }
 
-        throw new InvalidArgumentException(
-            sprintf(
-                'The json root does not match with the given pattern (error : %s)',
-                $matcher->getError()
-            )
-        );
-    }
-
-    /** @Then in the json, :path should match: */
-    final public function path_should_match(string $path, PyStringNode $pattern): void
-    {
-        $value = $this->getValue($path);
-        $matcher = $this->factory->createMatcher();
-
-        $json = json_encode($value);
-
-        if ($matcher->match($json, $pattern->getRaw())) {
-            return;
-        }
-
-        throw new InvalidArgumentException(
-            sprintf(
-                'The json path "%s" does not match with the given pattern (error : %s)',
-                $path,
-                $matcher->getError()
-            )
-        );
-    }
-
-    /** @Then in the json, :path should not match: */
-    final public function path_should_not_match(string $path, PyStringNode $pattern): void
-    {
-        $value = $this->getValue($path);
-        $matcher = $this->factory->createMatcher();
-
-        $json = json_encode($value);
-
-        if (!$matcher->match($json, $pattern->getRaw())) {
-            return;
-        }
+        $error = $matcher->getError();
+        assert(is_string($error));
 
         throw new InvalidArgumentException(
             sprintf(
-                'The json path "%s" matches with the given pattern (error : %s)',
-                $path,
-                $matcher->getError()
+                'The json root does not match with the given pattern (error : %s)',
+                $error
             )
         );
     }
-
-    private function getJson(): ?stdClass
-    {
-        return json_decode((string) $this->history->getLastResponse()->getBody());
-    }
-
-    private function getValue(string $path)
-    {
-        $json = $this->getJson();
-
-        if (null === $json) {
-            throw new InvalidArgumentException('Expected a Json valid content, got none');
-        }
-
-        return $this->accessor->getValue($json, $path);
-    }
 }