diff --git a/docs/README.md b/docs/README.md
index 0e509769f..23e57419b 100644
--- a/docs/README.md
+++ b/docs/README.md
@@ -6,6 +6,7 @@
 * [Available Checks](checks.md)
 * [AI-Powered Features & Configuration](ai-features.md)
 * [WordPress Functions Compatibility Data](wp-functions-compatibility-data.md)
+* [Plugin Check manifest](plugin-check-info.md)
 * [CLI Commands](CLI.md)
 * [Running Unit tests](running-unit-tests.md)
 * [Releasing a New Version of Plugin](releasing.md)
diff --git a/docs/plugin-check-info.md b/docs/plugin-check-info.md
new file mode 100644
index 000000000..7720f25f2
--- /dev/null
+++ b/docs/plugin-check-info.md
@@ -0,0 +1,16 @@
+# Plugin Check manifest
+
+Plugin authors can add `plugin-check-info.json` to plugin root to identify bundled third-party code.
+
+```json
+{
+    "third_parties": [
+        "vendor/phpseclib",
+        "libraries/legacy"
+    ]
+}
+```
+
+Plugin Check keeps errors from declared paths, but hides warning-level findings for those paths. This reduces recommendations intended for plugin authors, such as replacing a library's native PHP function with a WordPress wrapper, without hiding possible errors. Findings outside declared paths remain unchanged.
+
+Manifest is committed with plugin code, so reviewers can inspect declarations. Missing, malformed, or invalid manifest entries are ignored. Paths are relative to plugin root and use `/` separators. Entries match their declared path and files below it, not similarly named paths.
diff --git a/includes/Checker/Abstract_Check_Runner.php b/includes/Checker/Abstract_Check_Runner.php
index 8f66010ac..8ca38efa5 100644
--- a/includes/Checker/Abstract_Check_Runner.php
+++ b/includes/Checker/Abstract_Check_Runner.php
@@ -12,6 +12,7 @@
 use WordPress\Plugin_Check\Checker\Exception\Invalid_Check_Slug_Exception;
 use WordPress\Plugin_Check\Checker\Preparations\Universal_Runtime_Preparation;
 use WordPress\Plugin_Check\Traits\AI_Analyzer;
+use WordPress\Plugin_Check\Utilities\Plugin_Config;
 use WordPress\Plugin_Check\Utilities\Plugin_Request_Utility;
 
 /**
@@ -444,6 +445,8 @@ final public function run() {
 
 		$results = $this->get_checks_instance()->run_checks( $this->get_check_context(), $checks, $this );
 
+		$this->filter_third_party_warnings( $results );
+
 		$ai_analysis = array();
 		$ai_stats    = array();
 
@@ -473,6 +476,33 @@ final public function run() {
 		return $results;
 	}
 
+	/**
+	 * Removes warning-level findings from declared third-party paths.
+	 *
+	 * Errors and findings outside declared paths are kept unchanged.
+	 *
+	 * @since 2.1.0
+	 *
+	 * @param Check_Result $results Check results to filter, modified in place.
+	 */
+	private function filter_third_party_warnings( Check_Result $results ) {
+		$third_party_paths = Plugin_Config::get_third_party_paths( $this->get_check_context()->path() );
+
+		if ( empty( $third_party_paths ) ) {
+			return;
+		}
+
+		$results->transform_messages(
+			function ( $message, $is_error, $file ) use ( $third_party_paths ) {
+				if ( ! $is_error && Plugin_Config::is_third_party_file( $file, $third_party_paths ) ) {
+					return false;
+				}
+
+				return $message;
+			}
+		);
+	}
+
 	/**
 	 * Determines if any of the checks are a runtime check.
 	 *
diff --git a/includes/Utilities/Plugin_Config.php b/includes/Utilities/Plugin_Config.php
new file mode 100644
index 000000000..b738601ae
--- /dev/null
+++ b/includes/Utilities/Plugin_Config.php
@@ -0,0 +1,113 @@
+<?php
+/**
+ * Class WordPress\Plugin_Check\Utilities\Plugin_Config
+ *
+ * @package plugin-check
+ */
+
+namespace WordPress\Plugin_Check\Utilities;
+
+/**
+ * Reads optional plugin configuration.
+ *
+ * @since 2.1.0
+ */
+final class Plugin_Config {
+
+	/**
+	 * Configuration file name.
+	 *
+	 * @var string
+	 */
+	const FILE_NAME = 'plugin-check-info.json';
+
+	/**
+	 * Returns paths declared as third-party code.
+	 *
+	 * @since 2.1.0
+	 *
+	 * @param string $plugin_path Absolute plugin path.
+	 * @return string[] Relative third-party paths.
+	 */
+	public static function get_third_party_paths( $plugin_path ) {
+		$config_file = trailingslashit( $plugin_path ) . self::FILE_NAME;
+
+		if ( ! is_readable( $config_file ) ) {
+			return array();
+		}
+
+		// phpcs:ignore WordPress.WP.AlternativeFunctions.file_get_contents_file_get_contents -- Read plugin-local JSON configuration.
+		$contents = file_get_contents( $config_file );
+		if ( false === $contents ) {
+			return array();
+		}
+
+		$config = json_decode( $contents, true );
+
+		if ( ! is_array( $config ) || empty( $config['third_parties'] ) || ! is_array( $config['third_parties'] ) ) {
+			return array();
+		}
+
+		$paths = array();
+		foreach ( $config['third_parties'] as $path ) {
+			if ( ! is_string( $path ) ) {
+				continue;
+			}
+
+			$path = self::normalize_path( $path );
+			if ( '' !== $path ) {
+				$paths[] = $path;
+			}
+		}
+
+		return array_values( array_unique( $paths ) );
+	}
+
+	/**
+	 * Checks whether a relative file is inside a declared path.
+	 *
+	 * @since 2.1.0
+	 *
+	 * @param string   $file Relative file path.
+	 * @param string[] $paths Relative third-party paths.
+	 * @return bool Whether the file is inside a declared path.
+	 */
+	public static function is_third_party_file( $file, array $paths ) {
+		$file = self::normalize_path( $file );
+
+		if ( '' === $file ) {
+			return false;
+		}
+
+		foreach ( $paths as $path ) {
+			if ( $file === $path || 0 === strpos( $file, $path . '/' ) ) {
+				return true;
+			}
+		}
+
+		return false;
+	}
+
+	/**
+	 * Normalizes and validates a relative plugin path.
+	 *
+	 * @param string $path Plugin-relative path.
+	 * @return string Normalized path, or empty string when invalid.
+	 */
+	private static function normalize_path( $path ) {
+		$path = trim( str_replace( '\\', '/', $path ), " /\t\n\r\0\x0B" );
+
+		if ( '' === $path || '/' === substr( $path, 0, 1 ) || preg_match( '#^[A-Za-z]:/#', $path ) ) {
+			return '';
+		}
+
+		$segments = explode( '/', $path );
+		foreach ( $segments as $segment ) {
+			if ( '' === $segment || '.' === $segment || '..' === $segment ) {
+				return '';
+			}
+		}
+
+		return implode( '/', $segments );
+	}
+}
diff --git a/tests/phpunit/testdata/Checks/Warning_Check.php b/tests/phpunit/testdata/Checks/Warning_Check.php
new file mode 100644
index 000000000..1fab4b88f
--- /dev/null
+++ b/tests/phpunit/testdata/Checks/Warning_Check.php
@@ -0,0 +1,52 @@
+<?php
+
+namespace WordPress\Plugin_Check\Test_Data;
+
+use WordPress\Plugin_Check\Checker\Check_Categories;
+use WordPress\Plugin_Check\Checker\Check_Result;
+use WordPress\Plugin_Check\Checker\Static_Check;
+use WordPress\Plugin_Check\Traits\Stable_Check;
+
+class Warning_Check implements Static_Check {
+
+	use Stable_Check;
+
+	public function run( Check_Result $check_result ) {
+		$check_result->add_message(
+			false,
+			'Warning message',
+			array(
+				'code' => 'check_warning',
+				'file' => 'vendor/phpseclib/file.php',
+			)
+		);
+		$check_result->add_message(
+			false,
+			'Outside warning message',
+			array(
+				'code' => 'check_warning_outside',
+				'file' => 'includes/file.php',
+			)
+		);
+		$check_result->add_message(
+			true,
+			'Error message',
+			array(
+				'code' => 'check_error',
+				'file' => 'vendor/phpseclib/file.php',
+			)
+		);
+	}
+
+	public function get_categories() {
+		return array( Check_Categories::CATEGORY_GENERAL );
+	}
+
+	public function get_description(): string {
+		return '';
+	}
+
+	public function get_documentation_url(): string {
+		return '';
+	}
+}
diff --git a/tests/phpunit/testdata/plugins/test-plugin-plugin-check-info-invalid/load.php b/tests/phpunit/testdata/plugins/test-plugin-plugin-check-info-invalid/load.php
new file mode 100644
index 000000000..51c490e05
--- /dev/null
+++ b/tests/phpunit/testdata/plugins/test-plugin-plugin-check-info-invalid/load.php
@@ -0,0 +1,4 @@
+<?php
+/*
+ * Plugin Name: Test Plugin Invalid Config
+ */
diff --git a/tests/phpunit/testdata/plugins/test-plugin-plugin-check-info-invalid/plugin-check-info.json b/tests/phpunit/testdata/plugins/test-plugin-plugin-check-info-invalid/plugin-check-info.json
new file mode 100644
index 000000000..dd6e635cf
--- /dev/null
+++ b/tests/phpunit/testdata/plugins/test-plugin-plugin-check-info-invalid/plugin-check-info.json
@@ -0,0 +1 @@
+{"third_parties": ["vendor/phpseclib",]
\ No newline at end of file
diff --git a/tests/phpunit/testdata/plugins/test-plugin-plugin-check-info/load.php b/tests/phpunit/testdata/plugins/test-plugin-plugin-check-info/load.php
new file mode 100644
index 000000000..61fa5e70c
--- /dev/null
+++ b/tests/phpunit/testdata/plugins/test-plugin-plugin-check-info/load.php
@@ -0,0 +1,4 @@
+<?php
+/*
+ * Plugin Name: Test Plugin Config
+ */
diff --git a/tests/phpunit/testdata/plugins/test-plugin-plugin-check-info/plugin-check-info.json b/tests/phpunit/testdata/plugins/test-plugin-plugin-check-info/plugin-check-info.json
new file mode 100644
index 000000000..e29ad1876
--- /dev/null
+++ b/tests/phpunit/testdata/plugins/test-plugin-plugin-check-info/plugin-check-info.json
@@ -0,0 +1,6 @@
+{
+    "third_parties": [
+        "vendor\\phpseclib",
+        " /libraries/legacy/ "
+    ]
+}
diff --git a/tests/phpunit/tests/Checker/CLI_Runner_Tests.php b/tests/phpunit/tests/Checker/CLI_Runner_Tests.php
index f06600acb..383c42e1b 100644
--- a/tests/phpunit/tests/Checker/CLI_Runner_Tests.php
+++ b/tests/phpunit/tests/Checker/CLI_Runner_Tests.php
@@ -10,6 +10,7 @@
 use WordPress\Plugin_Check\Test_Data\Empty_Check;
 use WordPress\Plugin_Check\Test_Data\Error_Check;
 use WordPress\Plugin_Check\Test_Data\Runtime_Check;
+use WordPress\Plugin_Check\Test_Data\Warning_Check;
 use WordPress\Plugin_Check\Test_Utils\Traits\With_Mock_Filesystem;
 
 class CLI_Runner_Tests extends WP_UnitTestCase {
@@ -205,6 +206,32 @@ function ( $checks ) {
 		$this->assertNotEmpty( $results->get_errors() );
 	}
 
+	public function test_run_filters_third_party_warnings() {
+		$_SERVER['argv'] = array(
+			'wp',
+			'plugin',
+			'check',
+			UNIT_TESTS_PLUGIN_DIR . 'test-plugin-plugin-check-info',
+			'--checks=warning-check',
+		);
+
+		add_filter(
+			'wp_plugin_check_checks',
+			function () {
+				return array( 'warning-check' => new Warning_Check() );
+			}
+		);
+
+		$runner           = new CLI_Runner();
+		$cleanup          = $runner->prepare();
+		$this->cleanups[] = $cleanup;
+		$results          = $runner->run();
+
+		$this->assertArrayNotHasKey( 'vendor/phpseclib/file.php', $results->get_warnings() );
+		$this->assertArrayHasKey( 'includes/file.php', $results->get_warnings() );
+		$this->assertArrayHasKey( 'vendor/phpseclib/file.php', $results->get_errors() );
+	}
+
 	public function test_runner_initialized_early_throws_plugin_basename_exception() {
 		global $wp_actions;
 
diff --git a/tests/phpunit/tests/Checker/Check_Result_Tests.php b/tests/phpunit/tests/Checker/Check_Result_Tests.php
index 3015eddc9..95466ba32 100644
--- a/tests/phpunit/tests/Checker/Check_Result_Tests.php
+++ b/tests/phpunit/tests/Checker/Check_Result_Tests.php
@@ -188,4 +188,32 @@ public function test_get_error_count_with_message() {
 
 		$this->assertEquals( 1, $this->check_result->get_error_count() );
 	}
+
+	public function test_transform_messages_removes_messages_and_updates_counts() {
+		$this->check_result->add_message(
+			false,
+			'Third-party warning',
+			array(
+				'file' => 'test-plugin/vendor/library/file.php',
+			)
+		);
+		$this->check_result->add_message(
+			true,
+			'Third-party error',
+			array(
+				'file' => 'test-plugin/vendor/library/file.php',
+			)
+		);
+
+		$this->check_result->transform_messages(
+			function ( $message, $is_error, $file ) {
+				return $is_error || 0 !== strpos( $file, 'vendor/library/' ) ? $message : false;
+			}
+		);
+
+		$this->assertSame( 0, $this->check_result->get_warning_count() );
+		$this->assertSame( 1, $this->check_result->get_error_count() );
+		$this->assertEmpty( $this->check_result->get_warnings() );
+		$this->assertNotEmpty( $this->check_result->get_errors() );
+	}
 }
diff --git a/tests/phpunit/tests/Utilities/Plugin_Config_Tests.php b/tests/phpunit/tests/Utilities/Plugin_Config_Tests.php
new file mode 100644
index 000000000..9ab1b2ef3
--- /dev/null
+++ b/tests/phpunit/tests/Utilities/Plugin_Config_Tests.php
@@ -0,0 +1,43 @@
+<?php
+/**
+ * Tests for the Plugin_Config class.
+ *
+ * @package plugin-check
+ */
+
+use WordPress\Plugin_Check\Utilities\Plugin_Config;
+
+class Plugin_Config_Tests extends WP_UnitTestCase {
+
+	public function test_get_third_party_paths_returns_configured_paths() {
+		$paths = Plugin_Config::get_third_party_paths( UNIT_TESTS_PLUGIN_DIR . 'test-plugin-plugin-check-info' );
+
+		$this->assertSame( array( 'vendor/phpseclib', 'libraries/legacy' ), $paths );
+	}
+
+	public function test_get_third_party_paths_ignores_missing_config() {
+		$this->assertSame( array(), Plugin_Config::get_third_party_paths( UNIT_TESTS_PLUGIN_DIR . 'test-plugin-wp-functions-compatibility-with-errors' ) );
+	}
+
+	public function test_get_third_party_paths_ignores_invalid_config() {
+		$this->assertSame( array(), Plugin_Config::get_third_party_paths( UNIT_TESTS_PLUGIN_DIR . 'test-plugin-plugin-check-info-invalid' ) );
+	}
+
+	/**
+	 * @dataProvider third_party_file_provider
+	 */
+	public function test_is_third_party_file( $file, $expected ) {
+		$this->assertSame( $expected, Plugin_Config::is_third_party_file( $file, array( 'vendor/phpseclib' ) ) );
+	}
+
+	public function third_party_file_provider() {
+		return array(
+			'in declared directory'   => array( 'vendor/phpseclib/Crypt/Hash.php', true ),
+			'declared file'           => array( 'vendor/phpseclib', true ),
+			'near matching directory' => array( 'vendor/phpseclib2/Crypt/Hash.php', false ),
+			'outside directory'       => array( 'includes/Plugin.php', false ),
+			'normalizes backslashes'  => array( 'vendor\\phpseclib\\Crypt\\Hash.php', true ),
+			'rejects traversal'       => array( 'vendor/phpseclib/../other.php', false ),
+		);
+	}
+}