diff --git a/plugins/performance-lab/includes/server-timing/class-perflab-server-timing-metric.php b/plugins/performance-lab/includes/server-timing/class-perflab-server-timing-metric.php
index fc01e682c3..4d557a4eae 100644
--- a/plugins/performance-lab/includes/server-timing/class-perflab-server-timing-metric.php
+++ b/plugins/performance-lab/includes/server-timing/class-perflab-server-timing-metric.php
@@ -37,6 +37,14 @@ class Perflab_Server_Timing_Metric {
 	 */
 	private $before_value;
 
+	/**
+	 * The metric description.
+	 *
+	 * @since n.e.x.t
+	 * @var string|null
+	 */
+	private $description = null;
+
 	/**
 	 * Constructor.
 	 *
@@ -142,4 +150,36 @@ public function measure_after(): void {
 
 		$this->set_value( ( microtime( true ) - $this->before_value ) * 1000.0 );
 	}
+
+	/**
+	 * Sets the metric description.
+	 *
+	 * @since n.e.x.t
+	 *
+	 * @param non-empty-string $description The metric description.
+	 */
+	public function set_description( string $description ): void {
+		if ( 0 !== did_action( 'perflab_server_timing_send_header' ) && ! doing_action( 'perflab_server_timing_send_header' ) ) {
+			_doing_it_wrong(
+				__METHOD__,
+				/* translators: %s: WordPress action name */
+				sprintf( esc_html__( 'The method must be called before or during the %s action.', 'performance-lab' ), 'perflab_server_timing_send_header' ),
+				''
+			);
+			return;
+		}
+
+		$this->description = $description;
+	}
+
+	/**
+	 * Gets the metric description.
+	 *
+	 * @since n.e.x.t
+	 *
+	 * @return string|null The metric description, or null if none set.
+	 */
+	public function get_description(): ?string {
+		return $this->description;
+	}
 }
diff --git a/plugins/performance-lab/includes/server-timing/class-perflab-server-timing.php b/plugins/performance-lab/includes/server-timing/class-perflab-server-timing.php
index ba16cf6218..6e69553a92 100644
--- a/plugins/performance-lab/includes/server-timing/class-perflab-server-timing.php
+++ b/plugins/performance-lab/includes/server-timing/class-perflab-server-timing.php
@@ -290,23 +290,32 @@ function ( string $output, ?int $phase ): string {
 	 * @since 1.8.0
 	 *
 	 * @param Perflab_Server_Timing_Metric $metric The metric to format.
-	 * @return string|null Segment for the Server-Timing header, or null if no value set.
+	 * @return string Segment for the Server-Timing header.
 	 */
-	private function format_metric_header_value( Perflab_Server_Timing_Metric $metric ): ?string {
-		$value = $metric->get_value();
+	private function format_metric_header_value( Perflab_Server_Timing_Metric $metric ): string {
+		$value       = $metric->get_value();
+		$description = $metric->get_description();
 
-		// If no value is set, make sure it's just passed through.
-		if ( null === $value ) {
-			return null;
-		}
+		// See https://github.com/WordPress/performance/issues/955.
+		$name = preg_replace( '/[^!#$%&\'*+\-.^_`|~0-9a-zA-Z]/', '-', $metric->get_slug() );
+
+		$parts = array( sprintf( 'wp-%s', $name ) );
 
-		if ( is_float( $value ) ) {
-			$value = round( $value, 2 );
+		if ( null !== $value ) {
+			if ( is_float( $value ) ) {
+				$value = round( $value, 2 );
+			}
+			$parts[] = sprintf( 'dur=%s', $value );
 		}
 
-		// See https://github.com/WordPress/performance/issues/955.
-		$name = preg_replace( '/[^!#$%&\'*+\-.^_`|~0-9a-zA-Z]/', '-', $metric->get_slug() );
+		if ( null !== $description ) {
+			// Sanitize description for HTTP header quoted-string format.
+			// Remove control characters (CR/LF) and escape backslashes and quotes.
+			$sanitized_description = str_replace( array( "\r", "\n" ), '', $description );
+			$sanitized_description = addcslashes( $sanitized_description, '\\"' );
+			$parts[]               = sprintf( 'desc="%s"', $sanitized_description );
+		}
 
-		return sprintf( 'wp-%1$s;dur=%2$s', $name, $value );
+		return implode( ';', $parts );
 	}
 }
diff --git a/plugins/performance-lab/tests/includes/server-timing/test-perflab-server-timing-metric.php b/plugins/performance-lab/tests/includes/server-timing/test-perflab-server-timing-metric.php
index 842272f1c5..db35bad213 100644
--- a/plugins/performance-lab/tests/includes/server-timing/test-perflab-server-timing-metric.php
+++ b/plugins/performance-lab/tests/includes/server-timing/test-perflab-server-timing-metric.php
@@ -75,4 +75,20 @@ public function test_measure_after_without_before(): void {
 
 		$this->assertNull( $this->metric->get_value() );
 	}
+
+	/**
+	 * @covers Perflab_Server_Timing_Metric::set_description
+	 * @covers Perflab_Server_Timing_Metric::get_description
+	 */
+	public function test_set_description_with_string(): void {
+		$this->metric->set_description( 'Database queries' );
+		$this->assertSame( 'Database queries', $this->metric->get_description() );
+	}
+
+	/**
+	 * @covers Perflab_Server_Timing_Metric::get_description
+	 */
+	public function test_get_description_returns_null_by_default(): void {
+		$this->assertNull( $this->metric->get_description() );
+	}
 }
diff --git a/plugins/performance-lab/tests/includes/server-timing/test-perflab-server-timing.php b/plugins/performance-lab/tests/includes/server-timing/test-perflab-server-timing.php
index 561c3bb481..799d2c9250 100644
--- a/plugins/performance-lab/tests/includes/server-timing/test-perflab-server-timing.php
+++ b/plugins/performance-lab/tests/includes/server-timing/test-perflab-server-timing.php
@@ -7,6 +7,7 @@
 
 /**
  * @group server-timing
+ * @phpstan-import-type MetricArguments from Perflab_Server_Timing
  */
 class Test_Perflab_Server_Timing extends WP_UnitTestCase {
 
@@ -154,7 +155,8 @@ public function test_register_metric_replaces_slashes(): void {
 	/**
 	 * @dataProvider data_get_header
 	 *
-	 * @phpstan-param array<string, mixed> $metrics
+	 * @param string                         $expected The expected header value.
+	 * @param array<string, MetricArguments> $metrics  The metric configurations.
 	 */
 	public function test_get_header( string $expected, array $metrics ): void {
 		foreach ( $metrics as $metric_slug => $args ) {
@@ -281,4 +283,161 @@ public function test_use_output_buffer( callable $set_up, bool $expected ): void
 		$set_up();
 		$this->assertSame( $expected, $this->server_timing->use_output_buffer() );
 	}
+
+	/**
+	 * @dataProvider data_get_header_with_description
+	 *
+	 * @param string                         $expected The expected header value.
+	 * @param array<string, MetricArguments> $metrics  The metric configurations.
+	 */
+	public function test_get_header_with_description( string $expected, array $metrics ): void {
+		foreach ( $metrics as $metric_slug => $args ) {
+			$this->server_timing->register_metric( $metric_slug, $args );
+		}
+		$this->assertSame( $expected, $this->server_timing->get_header() );
+	}
+
+	/**
+	 * @return array<string, mixed>
+	 */
+	public function data_get_header_with_description(): array {
+		$measure_with_description = static function ( Perflab_Server_Timing_Metric $metric ): void {
+			$metric->set_value( 100 );
+			$metric->set_description( 'Database queries' );
+		};
+		$measure_description_only = static function ( Perflab_Server_Timing_Metric $metric ): void {
+			$metric->set_description( 'Cache operations' );
+		};
+		$measure_duration_only    = static function ( Perflab_Server_Timing_Metric $metric ): void {
+			$metric->set_value( 50 );
+		};
+		$measure_name_only        = static function ( Perflab_Server_Timing_Metric $metric ): void {
+			unset( $metric );
+		};
+
+		return array(
+			'metric with duration and description' => array(
+				'wp-db-query;dur=100;desc="Database queries"',
+				array(
+					'db-query' => array(
+						'measure_callback' => $measure_with_description,
+						'access_cap'       => 'exist',
+					),
+				),
+			),
+			'metric with description only'         => array(
+				'wp-cache-ops;desc="Cache operations"',
+				array(
+					'cache-ops' => array(
+						'measure_callback' => $measure_description_only,
+						'access_cap'       => 'exist',
+					),
+				),
+			),
+			'metric with duration only'            => array(
+				'wp-duration-only;dur=50',
+				array(
+					'duration-only' => array(
+						'measure_callback' => $measure_duration_only,
+						'access_cap'       => 'exist',
+					),
+				),
+			),
+			'metric with name only'                => array(
+				'wp-missed-cache',
+				array(
+					'missed-cache' => array(
+						'measure_callback' => $measure_name_only,
+						'access_cap'       => 'exist',
+					),
+				),
+			),
+			'mixed metrics'                        => array(
+				'wp-with-both;dur=100;desc="Database queries", wp-desc-only;desc="Cache operations", wp-dur-only;dur=50, wp-name-only',
+				array(
+					'with-both' => array(
+						'measure_callback' => $measure_with_description,
+						'access_cap'       => 'exist',
+					),
+					'desc-only' => array(
+						'measure_callback' => $measure_description_only,
+						'access_cap'       => 'exist',
+					),
+					'dur-only'  => array(
+						'measure_callback' => $measure_duration_only,
+						'access_cap'       => 'exist',
+					),
+					'name-only' => array(
+						'measure_callback' => $measure_name_only,
+						'access_cap'       => 'exist',
+					),
+				),
+			),
+		);
+	}
+
+	/**
+	 * @dataProvider data_get_header_with_description_edge_cases
+	 *
+	 * @param string                         $expected The expected header value.
+	 * @param array<string, MetricArguments> $metrics  The metric configurations.
+	 */
+	public function test_get_header_with_description_edge_cases( string $expected, array $metrics ): void {
+		foreach ( $metrics as $metric_slug => $args ) {
+			$this->server_timing->register_metric( $metric_slug, $args );
+		}
+		$this->assertSame( $expected, $this->server_timing->get_header() );
+	}
+
+	/**
+	 * @return array<string, mixed>
+	 */
+	public function data_get_header_with_description_edge_cases(): array {
+		return array(
+			'description with double quote'    => array(
+				'wp-quoted;desc="Say \\"hello\\""',
+				array(
+					'quoted' => array(
+						'measure_callback' => static function ( Perflab_Server_Timing_Metric $metric ): void {
+							$metric->set_description( 'Say "hello"' );
+						},
+						'access_cap'       => 'exist',
+					),
+				),
+			),
+			'description with backslash'       => array(
+				'wp-backslash;desc="path\\\\to\\\\file"',
+				array(
+					'backslash' => array(
+						'measure_callback' => static function ( Perflab_Server_Timing_Metric $metric ): void {
+							$metric->set_description( 'path\\to\\file' );
+						},
+						'access_cap'       => 'exist',
+					),
+				),
+			),
+			'description with newline'         => array(
+				'wp-newline;desc="Line 1Line 2"',
+				array(
+					'newline' => array(
+						'measure_callback' => static function ( Perflab_Server_Timing_Metric $metric ): void {
+							$metric->set_description( "Line 1\nLine 2" );
+						},
+						'access_cap'       => 'exist',
+					),
+				),
+			),
+			'description with carriage return' => array(
+				'wp-cr;desc="BeforeAfter"',
+				array(
+					'cr' => array(
+						'measure_callback' => static function ( Perflab_Server_Timing_Metric $metric ): void {
+							$metric->set_description( "Before\rAfter" );
+						},
+						'access_cap'       => 'exist',
+					),
+				),
+			),
+		);
+	}
 }