diff --git a/composer.json b/composer.json
index 71272a2..9af1771 100644
--- a/composer.json
+++ b/composer.json
@@ -20,6 +20,7 @@
     "homepage": "https://github.com/aternosorg/php-modrinth-api",
     "require": {
         "php": "^8.4.1",
+        "composer-runtime-api": "^2.0",
         "ext-curl": "*",
         "ext-json": "*",
         "ext-mbstring": "*",
diff --git a/composer.lock b/composer.lock
index 3c517fd..24fba47 100644
--- a/composer.lock
+++ b/composer.lock
@@ -4,7 +4,7 @@
         "Read more about it at https://getcomposer.org/doc/01-basic-usage.md#installing-dependencies",
         "This file is @generated automatically"
     ],
-    "content-hash": "693555b2f9c5b0d64c927f84b5f338c5",
+    "content-hash": "161653896c078b26e02472c96d5b0454",
     "packages": [
         {
             "name": "guzzlehttp/guzzle",
@@ -2624,6 +2624,7 @@
     "prefer-lowest": false,
     "platform": {
         "php": "^8.4.1",
+        "composer-runtime-api": "^2.0",
         "ext-curl": "*",
         "ext-json": "*",
         "ext-mbstring": "*"
diff --git a/src/Client/ModrinthAPIClient.php b/src/Client/ModrinthAPIClient.php
index 565d307..434ef68 100644
--- a/src/Client/ModrinthAPIClient.php
+++ b/src/Client/ModrinthAPIClient.php
@@ -47,6 +47,8 @@
 use Aternos\ModrinthApi\Model\User as UserModel;
 use Aternos\ModrinthApi\Model\UserPayoutHistory;
 use Aternos\ModrinthApi\Model\Version as VersionModel;
+use Composer\InstalledVersions;
+use OutOfBoundsException;
 use Psr\Http\Client\ClientInterface;
 
 
@@ -58,6 +60,11 @@
  */
 class ModrinthAPIClient
 {
+    /**
+     * Name of this package on packagist, used to look up the installed version
+     */
+    public const string PACKAGE_NAME = "aternos/modrinth-api";
+
     protected ?ClientInterface $httpClient;
 
     protected Configuration $configuration;
@@ -92,10 +99,34 @@ public function __construct(?string $apiToken = null, ?Configuration $configurat
     {
         $this->httpClient = $httpClient;
         $this->configuration = $configuration ?? (Configuration::getDefaultConfiguration())
-            ->setUserAgent("php-modrinth-api/2.0.0");
+            ->setUserAgent(static::getDefaultUserAgent());
         $this->setApiToken($apiToken);
     }
 
+    /**
+     * Get the installed version of this library, e.g. "4.0.0" or "dev-master"
+     * Returns "unknown" if the version cannot be determined, e.g. if the library was not installed using composer.
+     * @return string
+     */
+    public static function getLibraryVersion(): string
+    {
+        try {
+            return InstalledVersions::getPrettyVersion(static::PACKAGE_NAME) ?? "unknown";
+        } catch (OutOfBoundsException) {
+            return "unknown";
+        }
+    }
+
+    /**
+     * Get the user agent that identifies this library, e.g. "aternos/php-modrinth-api/4.0.0"
+     * It is used unless a different user agent is set with {@see setUserAgent()}.
+     * @return string
+     */
+    public static function getDefaultUserAgent(): string
+    {
+        return "aternos/php-modrinth-api/" . static::getLibraryVersion();
+    }
+
     /**
      * @param Configuration $configuration
      * @return $this
diff --git a/tests/Integration/Client/ClientTest.php b/tests/Integration/Client/ClientTest.php
index 27942a3..d9af96e 100644
--- a/tests/Integration/Client/ClientTest.php
+++ b/tests/Integration/Client/ClientTest.php
@@ -37,7 +37,7 @@ class ClientTest extends TestCase
     public function setUp(): void
     {
         $this->apiClient = new ModrinthAPIClient();
-        $this->apiClient->setUserAgent("aternos/php-modrinth-api@2.0.0 (contact@aternos.org)");
+        $this->apiClient->setUserAgent(ModrinthAPIClient::getDefaultUserAgent() . " (contact@aternos.org)");
     }
 
     protected function assertValidProjectList($list): void
diff --git a/tests/Unit/Client/ModrinthAPIClientTest.php b/tests/Unit/Client/ModrinthAPIClientTest.php
index a260c25..63188f8 100644
--- a/tests/Unit/Client/ModrinthAPIClientTest.php
+++ b/tests/Unit/Client/ModrinthAPIClientTest.php
@@ -14,9 +14,11 @@
 use Aternos\ModrinthApi\Client\User;
 use Aternos\ModrinthApi\Configuration;
 use Aternos\ModrinthApi\Model\UserPayoutHistory;
+use Composer\InstalledVersions;
 use GuzzleHttp\Client;
 use GuzzleHttp\Handler\MockHandler;
 use GuzzleHttp\HandlerStack;
+use GuzzleHttp\Middleware;
 use GuzzleHttp\Psr7\Response;
 use PHPUnit\Framework\Attributes\DataProvider;
 
@@ -31,7 +33,35 @@ public function testConstructorUsesDefaultConfiguration(): void
         $client = new ModrinthAPIClient();
 
         $this->assertInstanceOf(ModrinthAPIClient::class, $client);
-        $this->assertStringStartsWith("php-modrinth-api/", Configuration::getDefaultConfiguration()->getUserAgent());
+        $this->assertEquals(ModrinthAPIClient::getDefaultUserAgent(), Configuration::getDefaultConfiguration()->getUserAgent());
+    }
+
+    public function testGetLibraryVersionReturnsInstalledVersion(): void
+    {
+        $this->assertEquals(
+            InstalledVersions::getPrettyVersion(ModrinthAPIClient::PACKAGE_NAME),
+            ModrinthAPIClient::getLibraryVersion()
+        );
+        $this->assertNotEquals("unknown", ModrinthAPIClient::getLibraryVersion());
+    }
+
+    public function testDefaultUserAgentContainsPackageAndVersion(): void
+    {
+        $this->assertEquals(
+            "aternos/php-modrinth-api/" . ModrinthAPIClient::getLibraryVersion(),
+            ModrinthAPIClient::getDefaultUserAgent()
+        );
+    }
+
+    public function testDefaultUserAgentIsSentWithRequests(): void
+    {
+        $responses = [$this->fixtureResponse("get_project_response")];
+        $stack = HandlerStack::create(new MockHandler($responses));
+        $stack->push(Middleware::history($this->requests));
+        $client = new ModrinthAPIClient(null, null, new Client(['handler' => $stack]));
+
+        $client->getProject("modmenu");
+        $this->assertEquals(ModrinthAPIClient::getDefaultUserAgent(), $this->getRequest()->getHeaderLine("User-Agent"));
     }
 
     /**
@@ -52,7 +82,7 @@ public function testClientsWithoutExplicitConfigurationShareOne(): void
 
         // reset the shared configuration so that it cannot affect other tests
         Configuration::getDefaultConfiguration()
-            ->setUserAgent("php-modrinth-api/2.0.0")
+            ->setUserAgent(ModrinthAPIClient::getDefaultUserAgent())
             ->setApiKey("Authorization", null);
     }