diff --git a/composer.json b/composer.json
index 8d51c63..0444c71 100644
--- a/composer.json
+++ b/composer.json
@@ -54,5 +54,8 @@
 				"js/tests"
 			]
 		}
+	},
+	"scripts": {
+		"psalm": "psalm --config=config/psalm.xml"
 	}
 }
diff --git a/config/psalm.xml b/config/psalm.xml
new file mode 100644
index 0000000..5991740
--- /dev/null
+++ b/config/psalm.xml
@@ -0,0 +1,32 @@
+<?xml version="1.0"?>
+<psalm
+        totallyTyped="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"/>
+            <directory name="src/mustache/cache"/>
+        </ignoreFiles>
+    </projectFiles>
+
+    <issueHandlers>
+        <LessSpecificReturnType errorLevel="info"/>
+        <UndefinedFunction errorLevel="suppress"/>
+        <UndefinedClass>
+            <errorLevel type="suppress">
+                <referencedClass name="WP_Admin_Bar"/>
+                <referencedClass name="WP_Error"/>
+                <referencedClass name="WP_Hook"/>
+            </errorLevel>
+        </UndefinedClass>
+        <MixedArgument>
+            <errorLevel type="suppress">
+                <file name="src/Provider/Record_Provider.php" />
+            </errorLevel>
+        </MixedArgument>
+    </issueHandlers>
+</psalm>
diff --git a/src/Event/Hybrid_Events.php b/src/Event/Hybrid_Events.php
index 1df52d6..60f051c 100644
--- a/src/Event/Hybrid_Events.php
+++ b/src/Event/Hybrid_Events.php
@@ -21,6 +21,7 @@ class Hybrid_Events implements Hook_Event_Config_Interface {
 			return $events;
 		}
 
+		/** @var string $prefix */
 		$prefix = hybrid_get_prefix();
 
 		$events["{$prefix}_before_header"][10] = [
@@ -34,9 +35,11 @@ class Hybrid_Events implements Hook_Event_Config_Interface {
 			'category' => 'theme',
 		];
 
+		/** @var array $sidebars */
 		$sidebars = get_theme_support( 'hybrid-core-sidebars' );
 
 		if ( ! empty( $sidebars[0] ) ) {
+			/** @var string $sidebar */
 			foreach ( $sidebars[0] as $sidebar ) {
 
 				$events["{$prefix}_before_{$sidebar}"][10] = [
diff --git a/src/Formatter/Backtrace_Formatter.php b/src/Formatter/Backtrace_Formatter.php
index 242c421..8dc4352 100644
--- a/src/Formatter/Backtrace_Formatter.php
+++ b/src/Formatter/Backtrace_Formatter.php
@@ -8,7 +8,7 @@ namespace Rarst\Laps\Formatter;
  */
 class Backtrace_Formatter {
 
-	/** @var array $skip String matches to omit. */
+	/** @var string[] $skip String matches to omit. */
 	protected static $skip = [
 		'wp-blog-header.php',
 		'wp-load.php',
@@ -74,9 +74,13 @@ class Backtrace_Formatter {
 	}
 
 	/**
+	 *
 	 * @param string $item Backtrace item.
 	 *
 	 * @return string
+	 *
+	 * @psalm-suppress PossiblyFalseOperand
+	 * @psalm-suppress MixedInferredReturnType
 	 */
 	protected function shorten_include( string $item ): string {
 
diff --git a/src/Manager/Toolbar_Manager.php b/src/Manager/Toolbar_Manager.php
index 073630c..8a38e7d 100644
--- a/src/Manager/Toolbar_Manager.php
+++ b/src/Manager/Toolbar_Manager.php
@@ -29,6 +29,8 @@ class Toolbar_Manager {
 	 * Render interface and add to the toolbar.
 	 *
 	 * @param \WP_Admin_Bar $wp_admin_bar WordPress core toolbar object.
+	 *
+	 * @psalm-suppress MixedArgument
 	 */
 	public function admin_bar_menu( \WP_Admin_Bar $wp_admin_bar ): void {
 
diff --git a/src/Mustache_Cache_FrozenCache.php b/src/Mustache_Cache_FrozenCache.php
index a38fef5..08427c3 100644
--- a/src/Mustache_Cache_FrozenCache.php
+++ b/src/Mustache_Cache_FrozenCache.php
@@ -15,6 +15,8 @@ class Mustache_Cache_FrozenCache extends \Mustache_Cache_FilesystemCache {
 	 * @param string $value Value.
 	 *
 	 * @return void
+	 *
+	 * @psalm-suppress InvalidScalarArgument
 	 */
 	public function cache( $key, $value ): void {
 
diff --git a/src/Plugin.php b/src/Plugin.php
index 2716938..4af88ba 100644
--- a/src/Plugin.php
+++ b/src/Plugin.php
@@ -20,6 +20,9 @@ class Plugin extends Container {
 
 	/**
 	 * @param array $values Configuration values to apply.
+	 *
+	 * @psalm-suppress MixedArgument
+	 * @psalm-suppress MixedAssignment
 	 */
 	public function __construct( array $values = [] ) {
 
@@ -60,6 +63,8 @@ class Plugin extends Container {
 
 	/**
 	 * Start Stopwatch and timing plugin load immediately, then set up core events and needed hooks.
+	 *
+	 * @psalm-suppress MixedAssignment
 	 */
 	public function run(): void {
 
diff --git a/src/Record/Core_Load_Collector.php b/src/Record/Core_Load_Collector.php
index e39c41c..d946f3b 100644
--- a/src/Record/Core_Load_Collector.php
+++ b/src/Record/Core_Load_Collector.php
@@ -27,6 +27,10 @@ class Core_Load_Collector implements Record_Collector_Interface {
 
 		$request_time = filter_var( $_SERVER['REQUEST_TIME_FLOAT'], FILTER_VALIDATE_FLOAT );
 
+		/**
+		 * @var float $request_time
+		 * @var float $timestart
+		 */
 		return [
 			new Record( 'PHP Load', $request_time, $timestart - $request_time, '', 'php' ),
 			// TODO This includes network plugins on multisite, need conditional label if Laps is network–activated.
diff --git a/src/Record/Hook_Record_Collector.php b/src/Record/Hook_Record_Collector.php
index df99cba..2cd7373 100644
--- a/src/Record/Hook_Record_Collector.php
+++ b/src/Record/Hook_Record_Collector.php
@@ -18,8 +18,8 @@ class Hook_Record_Collector extends Stopwatch_Record_Collector {
 	protected $events = [];
 
 	/**
-	 * @param Stopwatch $stopwatch     Stopwatch instance.
-	 * @param array     $event_configs Starts and stops configuration.
+	 * @param Stopwatch                     $stopwatch     Stopwatch instance.
+	 * @param Hook_Event_Config_Interface[] $event_configs Starts and stops configuration.
 	 */
 	public function __construct( Stopwatch $stopwatch, array $event_configs ) {
 
@@ -42,7 +42,12 @@ class Hook_Record_Collector extends Stopwatch_Record_Collector {
 
 		$this->events = array_merge( $this->events, $stops );
 
+		/**
+		 * @var string $hook_name
+		 * @var array  $data
+		 */
 		foreach ( $stops as $hook_name => $data ) {
+			/** @var int $priority */
 			foreach ( array_keys( $data ) as $priority ) {
 				add_action( $hook_name, [ $this, 'tick' ], $priority );
 			}
@@ -70,8 +75,14 @@ class Hook_Record_Collector extends Stopwatch_Record_Collector {
 
 		global $wp_filter;
 
+		/** @var string $filter_name */
 		$filter_name     = current_filter();
+		/**
+		 * @var \WP_Hook|array $filter_instance
+		 * @var array<string,\WP_hook|array> $wp_filter
+		 */
 		$filter_instance = $wp_filter[ $filter_name ];
+		/** @var int $priority */
 		$priority        = $filter_instance instanceof \WP_Hook ? $filter_instance->current_priority() : key( $filter_instance );
 
 		// See https://core.trac.wordpress.org/ticket/41185 on broken priority, but more general sanity check.
diff --git a/src/Record/Recursive_Record_Iterator.php b/src/Record/Recursive_Record_Iterator.php
index 51ba241..c8945ce 100644
--- a/src/Record/Recursive_Record_Iterator.php
+++ b/src/Record/Recursive_Record_Iterator.php
@@ -8,7 +8,7 @@ namespace Rarst\Laps\Record;
  */
 class Recursive_Record_Iterator extends \ArrayIterator implements \RecursiveIterator {
 
-	/** @var array $children */
+	/** @var Record_Interface[] $children */
 	protected $children = [];
 
 	/**
diff --git a/src/Record/Sql_Record_Collector.php b/src/Record/Sql_Record_Collector.php
index 2ba0fa6..021b9d0 100644
--- a/src/Record/Sql_Record_Collector.php
+++ b/src/Record/Sql_Record_Collector.php
@@ -34,12 +34,15 @@ class Sql_Record_Collector implements Record_Collector_Interface {
 	 * @param string $query SQL query.
 	 *
 	 * @return string
+	 *
+	 * @psalm-suppress MixedPropertyFetch
 	 */
 	public function query( $query ): string {
 
 		global $wpdb;
 
 		if ( empty( $this->query_starts ) && ! empty( $wpdb->queries ) ) {
+			/** @var array $wpdb->queries */
 			$this->query_starts[ count( $wpdb->queries ) ] = microtime( true );
 		} else {
 			$this->query_starts[] = microtime( true );
@@ -59,6 +62,7 @@ class Sql_Record_Collector implements Record_Collector_Interface {
 
 		global $wpdb;
 
+		/** @var array $wpdb->queries */
 		return array_map( [ $this, 'transform' ], array_keys( $wpdb->queries ), $wpdb->queries );
 	}
 
@@ -75,6 +79,7 @@ class Sql_Record_Collector implements Record_Collector_Interface {
 	 *
 	 * @param int   $key        Query key in captured data.
 	 * @param array $query_data Array of captured query data.
+	 * @psalm-param array{0: string, 1: float, 2: string} $query_data
 	 *
 	 * @return Record
 	 */
@@ -84,6 +89,7 @@ class Sql_Record_Collector implements Record_Collector_Interface {
 
 		[ $sql, $duration, $caller ] = $query_data;
 
+		/** @var float $query_start */
 		$query_start = $this->query_starts[ $key ] ?? $last_query_end;
 		$sql         = trim( $sql );
 		$category    = 'sql-read';
diff --git a/src/Record/Stopwatch_Record_Collector.php b/src/Record/Stopwatch_Record_Collector.php
index 91ac9e2..8e5aed7 100644
--- a/src/Record/Stopwatch_Record_Collector.php
+++ b/src/Record/Stopwatch_Record_Collector.php
@@ -52,6 +52,7 @@ class Stopwatch_Record_Collector implements Record_Collector_Interface {
 
 		$events = $this->stopwatch->getSectionEvents( '__root__' );
 
+		/** @var string $name */
 		foreach ( array_keys( $events ) as $name ) {
 			if ( $this->stopwatch->isStarted( $name ) ) {
 				unset( $events[ $name ] );
diff --git a/src/Record/Timeline_Iterator.php b/src/Record/Timeline_Iterator.php
index 213f2c7..ec5200f 100644
--- a/src/Record/Timeline_Iterator.php
+++ b/src/Record/Timeline_Iterator.php
@@ -5,6 +5,8 @@ namespace Rarst\Laps\Record;
 
 /**
  * Processes records into sets for display by template.
+ *
+ * @psalm-suppress PropertyNotSetInConstructor
  */
 class Timeline_Iterator implements \Iterator {
 
@@ -22,6 +24,8 @@ class Timeline_Iterator implements \Iterator {
 
 	/**
 	 * @param Recursive_Record_Iterator $iterator Record iterator.
+	 *
+	 * @psalm-suppress PossiblyFalsePropertyAssignmentValue
 	 */
 	public function __construct( Recursive_Record_Iterator $iterator ) {
 
@@ -36,6 +40,7 @@ class Timeline_Iterator implements \Iterator {
 
 		$data = [];
 
+		/** @var Record $record */
 		foreach ( $this->current as $record ) {
 			$data[] = $this->prepare( $record );
 		}