diff --git a/composer.json b/composer.json
index f53002b..366a5cd 100644
--- a/composer.json
+++ b/composer.json
@@ -36,7 +36,7 @@
         "ext-json": "*",
         "phpunit/phpunit": "^9",
         "jetbrains/phpstorm-stubs": "^2019.3",
-        "psalm/phar": "6.20.*"
+        "psalm/phar": "^7.0.0-rc10"
     },
     "autoload": {
         "psr-4": {
diff --git a/examples/benchmark-memory.php b/examples/benchmark-memory.php
index 491d3de..9210989 100644
--- a/examples/benchmark-memory.php
+++ b/examples/benchmark-memory.php
@@ -11,6 +11,10 @@
 
 use Revolt\EventLoop;
 use Revolt\EventLoop\Driver;
+use Revolt\EventLoop\Driver\EvDriver;
+use Revolt\EventLoop\Driver\EventDriver;
+use Revolt\EventLoop\Driver\StreamSelectDriver;
+use Revolt\EventLoop\Driver\UvDriver;
 
 require __DIR__ . '/../vendor/autoload.php';
 
@@ -21,15 +25,17 @@
 
 /** @psalm-suppress RiskyCast */
 $t  = (int) \round((\array_key_exists('t', $args) ? (int) $args['t'] : 0));
-if (\array_key_exists('d', $args)) {
-    if (\is_string($args['d'])) {
-        $loopClass = 'Revolt\EventLoop\Driver\\' . $args['d'] . 'Driver';
-        if (\class_exists($loopClass)) {
-            $loop = new ($loopClass)();
-            if ($loop instanceof Driver) {
-                EventLoop::setDriver($loop);
-            }
-        }
+if (\array_key_exists('d', $args) && \is_string($args['d'])) {
+    $loop = match ($args['d']) {
+        'Ev' => EvDriver::isSupported() ? new EvDriver() : null,
+        'Event' => EventDriver::isSupported() ? new EventDriver() : null,
+        'StreamSelect' => new StreamSelectDriver(),
+        'Uv' => UvDriver::isSupported() ? new UvDriver() : null,
+        default => null,
+    };
+
+    if ($loop instanceof Driver) {
+        EventLoop::setDriver($loop);
     }
 }
 
diff --git a/examples/fiber-local-automatic.php b/examples/fiber-local-automatic.php
index 7a8d0c7..014efca 100644
--- a/examples/fiber-local-automatic.php
+++ b/examples/fiber-local-automatic.php
@@ -13,12 +13,17 @@
  * This might be used to log the current URL, authenticated user, or request identifier in an HTTP server.
  *
  * @psalm-suppress UnusedProperty
+ *
+ * @psalm-mutable
  */
 final class Logger
 {
     private int $nextId = 1;
     private FiberLocal $transactionId;
 
+    /**
+     * @psalm-capabilities read-props
+     */
     public function __construct()
     {
         $this->transactionId = new FiberLocal(fn () => $this->nextId++);
diff --git a/examples/fiber-local-manual.php b/examples/fiber-local-manual.php
index 04bb7fd..5ffe25c 100644
--- a/examples/fiber-local-manual.php
+++ b/examples/fiber-local-manual.php
@@ -14,10 +14,13 @@
  *
  * @psalm-suppress UnusedProperty
  */
-final class Logger
+final class ManualLogger
 {
     private FiberLocal $transactionId;
 
+    /**
+     * @psalm-capabilities read-props
+     */
     public function __construct()
     {
         $this->transactionId = new FiberLocal(fn () => throw new \Exception('Unknown transaction ID'));
@@ -45,7 +48,7 @@ public function log(string $message): void
     }
 }
 
-$logger = new Logger();
+$logger = new ManualLogger();
 $logger->setTransactionId(1);
 
 EventLoop::delay(1, static function () use ($logger) {
diff --git a/examples/http-client-suspension.php b/examples/http-client-suspension.php
index c15a3af..bcc3965 100644
--- a/examples/http-client-suspension.php
+++ b/examples/http-client-suspension.php
@@ -57,9 +57,15 @@ function fetch(string $url): string
     return $buffer;
 }
 
+/**
+ * Returns the header block of an HTTP response.
+ *
+ * @psalm-pure
+ */
 function extractHeader(string $httpResponse): string
 {
     return \explode("\r\n\r\n", $httpResponse, 2)[0];
 }
 
+// Printed on the CLI, where the header is text rather than HTML.
 echo extractHeader(fetch('http://www.google.com/'));
diff --git a/psalm.xml b/psalm.xml
index fd49f97..9cee111 100644
--- a/psalm.xml
+++ b/psalm.xml
@@ -15,12 +15,6 @@
     </projectFiles>
 
     <issueHandlers>
-        <DuplicateClass>
-            <errorLevel type="suppress">
-                <directory name="examples"/>
-            </errorLevel>
-        </DuplicateClass>
-
         <InvalidOperand>
             <errorLevel type="suppress">
                 <directory name="src/EventLoop/Driver"/>
@@ -98,6 +92,19 @@
                 <file name="src/EventLoop/Driver/EventDriver.php"/>
             </errorLevel>
         </UnusedVariable>
+
+        <!-- The example prints a raw response header to the CLI. -->
+        <TaintedHtml>
+            <errorLevel type="suppress">
+                <file name="examples/http-client-suspension.php"/>
+            </errorLevel>
+        </TaintedHtml>
+
+        <TaintedTextWithQuotes>
+            <errorLevel type="suppress">
+                <file name="examples/http-client-suspension.php"/>
+            </errorLevel>
+        </TaintedTextWithQuotes>
     </issueHandlers>
 
     <stubs>
diff --git a/src/EventLoop.php b/src/EventLoop.php
index a6b1fa1..6868b50 100644
--- a/src/EventLoop.php
+++ b/src/EventLoop.php
@@ -16,6 +16,9 @@
 /**
  * Accessor to allow global access to the event loop.
  *
+ * Scheduling and suspension are `io` for callers, like `usleep()`: the driver is the scheduler, and
+ * what other fibers do while the current one is suspended is their own effect.
+ *
  * @see Driver
  */
 final class EventLoop
@@ -35,24 +38,36 @@ public static function setDriver(Driver $driver): void
         try {
             /** @psalm-suppress InternalClass */
             self::$driver = new class () extends AbstractDriver {
+                /**
+                 * @psalm-pure
+                 */
                 #[\Override]
                 protected function activate(array $callbacks): void
                 {
                     throw new \Error("Can't activate callback during garbage collection.");
                 }
 
+                /**
+                 * @psalm-pure
+                 */
                 #[\Override]
                 protected function dispatch(bool $blocking): void
                 {
                     throw new \Error("Can't dispatch during garbage collection.");
                 }
 
+                /**
+                 * @psalm-capabilities read-props
+                 */
                 #[\Override]
                 protected function deactivate(DriverCallback $callback): void
                 {
                     // do nothing
                 }
 
+                /**
+                 * @psalm-pure
+                 */
                 #[\Override]
                 public function getHandle(): mixed
                 {
@@ -83,6 +98,9 @@ protected function now(): float
      *
      * @param \Closure(...):void $closure The callback to queue.
      * @param mixed ...$args The callback arguments.
+     *
+     * @psalm-capabilities io
+     * @psalm-suppress ImpureMethodCall
      */
     public static function queue(\Closure $closure, mixed ...$args): void
     {
@@ -102,6 +120,9 @@ public static function queue(\Closure $closure, mixed ...$args): void
      *     invalidated before the callback invocation.
      *
      * @return string A unique identifier that can be used to cancel, enable or disable the callback.
+     *
+     * @psalm-capabilities io
+     * @psalm-suppress ImpureMethodCall
      */
     public static function defer(\Closure $closure): string
     {
@@ -122,6 +143,9 @@ public static function defer(\Closure $closure): string
      *     before the callback invocation.
      *
      * @return string A unique identifier that can be used to cancel, enable or disable the callback.
+     *
+     * @psalm-capabilities io
+     * @psalm-suppress ImpureMethodCall
      */
     public static function delay(float $delay, \Closure $closure): string
     {
@@ -142,6 +166,9 @@ public static function delay(float $delay, \Closure $closure): string
      * @param \Closure(string):void $closure The callback to repeat.
      *
      * @return string A unique identifier that can be used to cancel, enable or disable the callback.
+     *
+     * @psalm-capabilities io
+     * @psalm-suppress ImpureMethodCall
      */
     public static function repeat(float $interval, \Closure $closure): string
     {
@@ -165,6 +192,9 @@ public static function repeat(float $interval, \Closure $closure): string
      * @param \Closure(string, resource):void $closure The callback to execute.
      *
      * @return string A unique identifier that can be used to cancel, enable or disable the callback.
+     *
+     * @psalm-capabilities io
+     * @psalm-suppress ImpureMethodCall
      */
     public static function onReadable(mixed $stream, \Closure $closure): string
     {
@@ -188,6 +218,9 @@ public static function onReadable(mixed $stream, \Closure $closure): string
      * @param \Closure(string, resource):void $closure The callback to execute.
      *
      * @return string A unique identifier that can be used to cancel, enable or disable the callback.
+     *
+     * @psalm-capabilities io
+     * @psalm-suppress ImpureMethodCall
      */
     public static function onWritable(mixed $stream, \Closure $closure): string
     {
@@ -212,6 +245,9 @@ public static function onWritable(mixed $stream, \Closure $closure): string
      * @return string A unique identifier that can be used to cancel, enable or disable the callback.
      *
      * @throws UnsupportedFeatureException If signal handling is not supported.
+     *
+     * @psalm-capabilities io
+     * @psalm-suppress ImpureMethodCall
      */
     public static function onSignal(int $signal, \Closure $closure): string
     {
@@ -229,6 +265,9 @@ public static function onSignal(int $signal, \Closure $closure): string
      * @return string The callback identifier.
      *
      * @throws InvalidCallbackError If the callback identifier is invalid.
+     *
+     * @psalm-capabilities io
+     * @psalm-suppress ImpureMethodCall
      */
     public static function enable(string $callbackId): string
     {
@@ -247,6 +286,9 @@ public static function enable(string $callbackId): string
      * @param string $callbackId The callback identifier.
      *
      * @return string The callback identifier.
+     *
+     * @psalm-capabilities io
+     * @psalm-suppress ImpureMethodCall
      */
     public static function disable(string $callbackId): string
     {
@@ -260,6 +302,9 @@ public static function disable(string $callbackId): string
      * callback is permanently invalid. Calling this function MUST NOT fail, even if passed an invalid identifier.
      *
      * @param string $callbackId The callback identifier.
+     *
+     * @psalm-capabilities io
+     * @psalm-suppress ImpureMethodCall
      */
     public static function cancel(string $callbackId): void
     {
@@ -277,6 +322,9 @@ public static function cancel(string $callbackId): void
      * @return string The callback identifier.
      *
      * @throws InvalidCallbackError If the callback identifier is invalid.
+     *
+     * @psalm-capabilities io
+     * @psalm-suppress ImpureMethodCall
      */
     public static function reference(string $callbackId): string
     {
@@ -292,6 +340,9 @@ public static function reference(string $callbackId): string
      * @param string $callbackId The callback identifier.
      *
      * @return string The callback identifier.
+     *
+     * @psalm-capabilities io
+     * @psalm-suppress ImpureMethodCall
      */
     public static function unreference(string $callbackId): string
     {
@@ -352,6 +403,9 @@ public static function getType(string $callbackId): CallbackType
      * @param string $callbackId The callback identifier.
      *
      * @return bool `true` if the callback is currently enabled, otherwise `false`.
+     *
+     * @psalm-capabilities io
+     * @psalm-suppress ImpureMethodCall
      */
     public static function isEnabled(string $callbackId): bool
     {
@@ -364,6 +418,9 @@ public static function isEnabled(string $callbackId): bool
      * @param string $callbackId The callback identifier.
      *
      * @return bool `true` if the callback is currently referenced, otherwise `false`.
+     *
+     * @psalm-capabilities io
+     * @psalm-suppress ImpureMethodCall
      */
     public static function isReferenced(string $callbackId): bool
     {
@@ -391,6 +448,9 @@ public static function getDriver(): Driver
      * Calls from the same fiber will return the same suspension object.
      *
      * @return Suspension
+     *
+     * @psalm-capabilities io
+     * @psalm-suppress ImpureMethodCall
      */
     public static function getSuspension(): Suspension
     {
@@ -415,6 +475,8 @@ public static function run(): void
      * Disable construction as this is a static class.
      *
      * @psalm-suppress UnusedConstructor
+     *
+     * @psalm-capabilities read-props
      */
     private function __construct()
     {
diff --git a/src/EventLoop/Driver.php b/src/EventLoop/Driver.php
index 80464aa..ceea32c 100644
--- a/src/EventLoop/Driver.php
+++ b/src/EventLoop/Driver.php
@@ -7,6 +7,8 @@
 /**
  * The driver MUST run in its own fiber and execute callbacks in a separate fiber. If fibers are reused, the driver
  * needs to call {@see FiberLocal::clear()} after running the callback.
+ *
+ * @psalm-mutable
  */
 interface Driver
 {
@@ -24,6 +26,8 @@ interface Driver
      * error handler or exceptions that would be passed to an error handler but none exists to handle them.
      *
      * @throws \Error Thrown if the event loop is already running.
+     *
+     * @psalm-impure
      */
     public function run(): void;
 
@@ -32,6 +36,8 @@ public function run(): void;
      *
      * When an event loop is stopped, it continues with its current tick and exits the loop afterwards. Multiple calls
      * to stop MUST be ignored and MUST NOT raise an exception.
+     *
+     * @psalm-impure
      */
     public function stop(): void;
 
@@ -41,11 +47,15 @@ public function stop(): void;
      * Calls from the same fiber will return the same suspension object.
      *
      * @return Suspension
+     *
+     * @psalm-impure
      */
     public function getSuspension(): Suspension;
 
     /**
      * @return bool True if the event loop is running, false if it is stopped.
+     *
+     * @psalm-impure
      */
     public function isRunning(): bool;
 
@@ -60,6 +70,8 @@ public function isRunning(): bool;
      *
      * @param \Closure(...):void $closure The callback to queue.
      * @param mixed ...$args The callback arguments.
+     *
+     * @psalm-impure
      */
     public function queue(\Closure $closure, mixed ...$args): void;
 
@@ -76,6 +88,8 @@ public function queue(\Closure $closure, mixed ...$args): void;
      *     callback invocation.
      *
      * @return string A unique identifier that can be used to cancel, enable or disable the callback.
+     *
+     * @psalm-impure
      */
     public function defer(\Closure $closure): string;
 
@@ -93,6 +107,8 @@ public function defer(\Closure $closure): string;
      *     callback invocation.
      *
      * @return string A unique identifier that can be used to cancel, enable or disable the callback.
+     *
+     * @psalm-impure
      */
     public function delay(float $delay, \Closure $closure): string;
 
@@ -110,6 +126,8 @@ public function delay(float $delay, \Closure $closure): string;
      * @param \Closure(string):void $closure The callback to repeat.
      *
      * @return string A unique identifier that can be used to cancel, enable or disable the callback.
+     *
+     * @psalm-impure
      */
     public function repeat(float $interval, \Closure $closure): string;
 
@@ -130,6 +148,8 @@ public function repeat(float $interval, \Closure $closure): string;
      * @param \Closure(string, resource):void $closure The callback to execute.
      *
      * @return string A unique identifier that can be used to cancel, enable or disable the callback.
+     *
+     * @psalm-impure
      */
     public function onReadable(mixed $stream, \Closure $closure): string;
 
@@ -150,6 +170,8 @@ public function onReadable(mixed $stream, \Closure $closure): string;
      * @param \Closure(string, resource):void $closure The callback to execute.
      *
      * @return string A unique identifier that can be used to cancel, enable or disable the callback.
+     *
+     * @psalm-impure
      */
     public function onWritable(mixed $stream, \Closure $closure): string;
 
@@ -171,6 +193,8 @@ public function onWritable(mixed $stream, \Closure $closure): string;
      * @return string A unique identifier that can be used to cancel, enable or disable the callback.
      *
      * @throws UnsupportedFeatureException If signal handling is not supported.
+     *
+     * @psalm-impure
      */
     public function onSignal(int $signal, \Closure $closure): string;
 
@@ -185,6 +209,8 @@ public function onSignal(int $signal, \Closure $closure): string;
      * @return string The callback identifier.
      *
      * @throws InvalidCallbackError If the callback identifier is invalid.
+     *
+     * @psalm-impure
      */
     public function enable(string $callbackId): string;
 
@@ -195,6 +221,8 @@ public function enable(string $callbackId): string;
      * callback is permanently invalid. Calling this function MUST NOT fail, even if passed an invalid identifier.
      *
      * @param string $callbackId The callback identifier.
+     *
+     * @psalm-impure
      */
     public function cancel(string $callbackId): void;
 
@@ -210,6 +238,8 @@ public function cancel(string $callbackId): void;
      * @param string $callbackId The callback identifier.
      *
      * @return string The callback identifier.
+     *
+     * @psalm-impure
      */
     public function disable(string $callbackId): string;
 
@@ -224,6 +254,8 @@ public function disable(string $callbackId): string;
      * @return string The callback identifier.
      *
      * @throws InvalidCallbackError If the callback identifier is invalid.
+     *
+     * @psalm-impure
      */
     public function reference(string $callbackId): string;
 
@@ -236,6 +268,8 @@ public function reference(string $callbackId): string;
      * @param string $callbackId The callback identifier.
      *
      * @return string The callback identifier.
+     *
+     * @psalm-impure
      */
     public function unreference(string $callbackId): string;
 
@@ -250,6 +284,8 @@ public function unreference(string $callbackId): string;
      *
      * @param null|\Closure(\Throwable):void $errorHandler The callback to execute. `null` will clear the current
      *     handler.
+     *
+     * @psalm-impure
      */
     public function setErrorHandler(?\Closure $errorHandler): void;
 
@@ -257,6 +293,8 @@ public function setErrorHandler(?\Closure $errorHandler): void;
      * Gets the error handler closure or {@code null} if none is set.
      *
      * @return null|\Closure(\Throwable):void The previous handler, `null` if there was none.
+     *
+     * @psalm-impure
      */
     public function getErrorHandler(): ?\Closure;
 
@@ -270,6 +308,8 @@ public function getErrorHandler(): ?\Closure;
      * instance.
      *
      * @return null|object|resource The loop handle the event loop operates on. `null` if there is none.
+     *
+     * @psalm-impure
      */
     public function getHandle(): mixed;
 
@@ -277,6 +317,8 @@ public function getHandle(): mixed;
      * Returns all registered non-cancelled callback identifiers.
      *
      * @return string[] Callback identifiers.
+     *
+     * @psalm-impure
      */
     public function getIdentifiers(): array;
 
@@ -286,6 +328,8 @@ public function getIdentifiers(): array;
      * @param string $callbackId The callback identifier.
      *
      * @return CallbackType The callback type.
+     *
+     * @psalm-impure
      */
     public function getType(string $callbackId): CallbackType;
 
@@ -295,6 +339,8 @@ public function getType(string $callbackId): CallbackType;
      * @param string $callbackId The callback identifier.
      *
      * @return bool `true` if the callback is currently enabled, otherwise `false`.
+     *
+     * @psalm-impure
      */
     public function isEnabled(string $callbackId): bool;
 
@@ -304,6 +350,8 @@ public function isEnabled(string $callbackId): bool;
      * @param string $callbackId The callback identifier.
      *
      * @return bool `true` if the callback is currently referenced, otherwise `false`.
+     *
+     * @psalm-impure
      */
     public function isReferenced(string $callbackId): bool;
 
@@ -313,6 +361,8 @@ public function isReferenced(string $callbackId): bool;
      * If this method isn't implemented, dumping the event loop in a busy application, even indirectly, is a pain.
      *
      * @return array
+     *
+     * @psalm-impure
      */
     public function __debugInfo(): array;
 }
diff --git a/src/EventLoop/Driver/EvDriver.php b/src/EventLoop/Driver/EvDriver.php
index 9699664..60caa25 100644
--- a/src/EventLoop/Driver/EvDriver.php
+++ b/src/EventLoop/Driver/EvDriver.php
@@ -19,6 +19,9 @@ final class EvDriver extends AbstractDriver
     /** @var array<string, \EvSignal>|null */
     private static ?array $activeSignals = null;
 
+    /**
+     * @psalm-pure
+     */
     public static function isSupported(): bool
     {
         return \extension_loaded("ev");
diff --git a/src/EventLoop/Driver/EventDriver.php b/src/EventLoop/Driver/EventDriver.php
index 36b6040..02e0a50 100644
--- a/src/EventLoop/Driver/EventDriver.php
+++ b/src/EventLoop/Driver/EventDriver.php
@@ -19,6 +19,9 @@ final class EventDriver extends AbstractDriver
     /** @var array<string, \Event>|null */
     private static ?array $activeSignals = null;
 
+    /**
+     * @psalm-pure
+     */
     public static function isSupported(): bool
     {
         return \extension_loaded("event");
diff --git a/src/EventLoop/Driver/StreamSelectDriver.php b/src/EventLoop/Driver/StreamSelectDriver.php
index d072ff3..1f634cd 100644
--- a/src/EventLoop/Driver/StreamSelectDriver.php
+++ b/src/EventLoop/Driver/StreamSelectDriver.php
@@ -53,7 +53,10 @@ public function __construct()
             && \function_exists('pcntl_signal_dispatch')
             && \function_exists('pcntl_signal');
 
-        $this->streamSelectErrorHandler = function (int $errno, string $message): void {
+        $this->streamSelectErrorHandler = /**
+         * @psalm-capabilities read-props|write-this-props|write-refs
+         */
+        function (int $errno, string $message): void {
             // Casing changed in PHP 8 from 'unable' to 'Unable'
             if (\stripos($message, "stream_select(): unable to select [4]: ") === 0) { // EINTR
                 $this->streamSelectIgnoreResult = true;
@@ -102,6 +105,9 @@ public function onSignal(int $signal, \Closure $closure): string
         return parent::onSignal($signal, $closure);
     }
 
+    /**
+     * @psalm-pure
+     */
     #[\Override]
     public function getHandle(): mixed
     {
diff --git a/src/EventLoop/Driver/TracingDriver.php b/src/EventLoop/Driver/TracingDriver.php
index 1888e99..4951f63 100644
--- a/src/EventLoop/Driver/TracingDriver.php
+++ b/src/EventLoop/Driver/TracingDriver.php
@@ -207,6 +207,9 @@ public function getHandle(): mixed
         return $this->driver->getHandle();
     }
 
+    /**
+     * @psalm-capabilities read-props
+     */
     public function dump(): string
     {
         $dump = "Enabled, referenced callbacks keeping the loop running: ";
@@ -260,11 +263,17 @@ public function queue(\Closure $closure, mixed ...$args): void
         $this->driver->queue($closure, ...$args);
     }
 
+    /**
+     * @psalm-capabilities read-props
+     */
     private function getCreationTrace(string $callbackId): string
     {
         return $this->creationTraces[$callbackId] ?? 'No creation trace, yet.';
     }
 
+    /**
+     * @psalm-capabilities read-props
+     */
     private function getCancelTrace(string $callbackId): string
     {
         return $this->cancelTraces[$callbackId] ?? 'No cancellation trace, yet.';
@@ -284,6 +293,8 @@ private function getCancelTrace(string $callbackId): string
      * }> $trace Output of `debug_backtrace()`.
      *
      * @return string Formatted stacktrace.
+     *
+     * @psalm-pure
      */
     private function formatStacktrace(array $trace): string
     {
diff --git a/src/EventLoop/Driver/UvDriver.php b/src/EventLoop/Driver/UvDriver.php
index 98c81dd..d213fba 100644
--- a/src/EventLoop/Driver/UvDriver.php
+++ b/src/EventLoop/Driver/UvDriver.php
@@ -14,6 +14,9 @@
 
 final class UvDriver extends AbstractDriver
 {
+    /**
+     * @psalm-pure
+     */
     public static function isSupported(): bool
     {
         return \extension_loaded("uv");
@@ -129,6 +132,9 @@ public function getHandle(): mixed
         return $this->handle;
     }
 
+    /**
+     * @psalm-capabilities read-props
+     */
     #[\Override]
     protected function now(): float
     {
@@ -138,6 +144,9 @@ protected function now(): float
         return \uv_now($this->handle) / 1000;
     }
 
+    /**
+     * @psalm-capabilities read-props
+     */
     #[\Override]
     protected function dispatch(bool $blocking): void
     {
@@ -145,6 +154,9 @@ protected function dispatch(bool $blocking): void
         \uv_run($this->handle, $blocking ? \UV::RUN_ONCE : \UV::RUN_NOWAIT);
     }
 
+    /**
+     * @psalm-capabilities read-props|write-this-props|write-refs
+     */
     #[\Override]
     protected function activate(array $callbacks): void
     {
@@ -213,6 +225,9 @@ protected function activate(array $callbacks): void
         }
     }
 
+    /**
+     * @psalm-capabilities read-props
+     */
     #[\Override]
     protected function deactivate(DriverCallback $callback): void
     {
@@ -252,6 +267,9 @@ protected function deactivate(DriverCallback $callback): void
         }
     }
 
+    /**
+     * @psalm-pure
+     */
     private function getStreamCallbackFlags(StreamCallback $callback): int
     {
         if ($callback instanceof StreamWritableCallback) {
diff --git a/src/EventLoop/FiberLocal.php b/src/EventLoop/FiberLocal.php
index 34dd261..395d87f 100644
--- a/src/EventLoop/FiberLocal.php
+++ b/src/EventLoop/FiberLocal.php
@@ -10,6 +10,8 @@
  * Each instance stores data separately for each fiber. Usage examples include contextual logging data.
  *
  * @template T
+ *
+ * @api
  */
 final class FiberLocal
 {
diff --git a/src/EventLoop/Internal/AbstractDriver.php b/src/EventLoop/Internal/AbstractDriver.php
index ef7513b..8e6236b 100644
--- a/src/EventLoop/Internal/AbstractDriver.php
+++ b/src/EventLoop/Internal/AbstractDriver.php
@@ -131,6 +131,9 @@ public function stop(): void
         $this->stopped = true;
     }
 
+    /**
+     * @psalm-capabilities read-props
+     */
     #[\Override]
     public function isRunning(): bool
     {
@@ -143,6 +146,9 @@ public function queue(\Closure $closure, mixed ...$args): void
         $this->microtaskQueue->enqueue([$closure, $args]);
     }
 
+    /**
+     * @psalm-capabilities read-props|write-this-props|write-refs
+     */
     #[\Override]
     public function defer(\Closure $closure): string
     {
@@ -184,6 +190,9 @@ public function repeat(float $interval, \Closure $closure): string
         return $timerCallback->id;
     }
 
+    /**
+     * @psalm-capabilities read-props|write-this-props|write-refs
+     */
     #[\Override]
     public function onReadable(mixed $stream, \Closure $closure): string
     {
@@ -195,6 +204,9 @@ public function onReadable(mixed $stream, \Closure $closure): string
         return $streamCallback->id;
     }
 
+    /**
+     * @psalm-capabilities read-props|write-this-props|write-refs
+     */
     #[\Override]
     public function onWritable($stream, \Closure $closure): string
     {
@@ -333,6 +345,9 @@ public function getSuspension(): Suspension
         return $suspension;
     }
 
+    /**
+     * @psalm-capabilities read-props|write-this-props|write-refs
+     */
     #[\Override]
     public function setErrorHandler(?\Closure $errorHandler): void
     {
@@ -345,6 +360,9 @@ public function getErrorHandler(): ?\Closure
         return $this->errorHandler;
     }
 
+    /**
+     * @psalm-capabilities read-props
+     */
     #[\Override]
     public function __debugInfo(): array
     {
@@ -357,12 +375,18 @@ public function __debugInfo(): array
         // @codeCoverageIgnoreEnd
     }
 
+    /**
+     * @psalm-capabilities read-props
+     */
     #[\Override]
     public function getIdentifiers(): array
     {
         return \array_keys($this->callbacks);
     }
 
+    /**
+     * @psalm-capabilities read-props
+     */
     #[\Override]
     public function getType(string $callbackId): CallbackType
     {
@@ -371,6 +395,9 @@ public function getType(string $callbackId): CallbackType
         return $callback->getType();
     }
 
+    /**
+     * @psalm-capabilities read-props
+     */
     #[\Override]
     public function isEnabled(string $callbackId): bool
     {
@@ -379,6 +406,9 @@ public function isEnabled(string $callbackId): bool
         return $callback->enabled;
     }
 
+    /**
+     * @psalm-capabilities read-props
+     */
     #[\Override]
     public function isReferenced(string $callbackId): bool
     {
@@ -391,16 +421,22 @@ public function isReferenced(string $callbackId): bool
      * Activates (enables) all the given callbacks.
      *
      * @param array<string, DriverCallback> $callbacks
+     *
+     * @psalm-impure
      */
     abstract protected function activate(array $callbacks): void;
 
     /**
      * Dispatches any pending read/write, timer, and signal events.
+     *
+     * @psalm-impure
      */
     abstract protected function dispatch(bool $blocking): void;
 
     /**
      * Deactivates (disables) the given callback.
+     *
+     * @psalm-impure
      */
     abstract protected function deactivate(DriverCallback $callback): void;
 
@@ -436,6 +472,8 @@ final protected function error(\Closure $closure, \Throwable $exception): void
      *
      * Note this value does not necessarily correlate to wall-clock time, rather the value returned is meant to be used
      * in relative comparisons to prior values returned by this method (intervals, expiration calculations, etc.).
+     *
+     * @psalm-impure
      */
     abstract protected function now(): float;
 
@@ -464,6 +502,8 @@ private function invokeMicrotasks(): void
 
     /**
      * @return bool True if no enabled and referenced callbacks remain in the loop.
+     *
+     * @psalm-capabilities read-props
      */
     private function isEmpty(): bool
     {
@@ -538,6 +578,8 @@ private function invokeCallbacks(): void
 
     /**
      * @param \Closure():mixed $interrupt
+     *
+     * @psalm-capabilities read-props|write-this-props|write-refs
      */
     private function setInterrupt(\Closure $interrupt): void
     {
@@ -546,6 +588,9 @@ private function setInterrupt(\Closure $interrupt): void
         $this->interrupt = $interrupt;
     }
 
+    /**
+     * @psalm-capabilities read-props|write-this-props|write-refs
+     */
     private function invokeInterrupt(): void
     {
         \assert($this->interrupt !== null);
@@ -663,6 +708,9 @@ private function createErrorCallback(): void
         };
     }
 
+    /**
+     * @psalm-capabilities read-props|write-this-props|write-refs
+     */
     private function callbackId(): string
     {
         $callbackId = $this->nextId;
@@ -677,6 +725,9 @@ private function callbackId(): string
         return $callbackId;
     }
 
+    /**
+     * @psalm-pure
+     */
     final public function __serialize(): never
     {
         throw new \Error(__CLASS__ . ' does not support serialization');
@@ -684,6 +735,8 @@ final public function __serialize(): never
 
     /**
      * @psalm-suppress UnusedParam $data param required.
+     *
+     * @psalm-pure
      */
     final public function __unserialize(array $data): never
     {
diff --git a/src/EventLoop/Internal/ClosureHelper.php b/src/EventLoop/Internal/ClosureHelper.php
index 48f8fa2..da7478b 100644
--- a/src/EventLoop/Internal/ClosureHelper.php
+++ b/src/EventLoop/Internal/ClosureHelper.php
@@ -4,9 +4,16 @@
 
 namespace Revolt\EventLoop\Internal;
 
-/** @internal */
+/**
+ * @internal
+ *
+ * @psalm-immutable
+ */
 final class ClosureHelper
 {
+    /**
+     * @psalm-capabilities read-props
+     */
     public static function getDescription(\Closure $closure): string
     {
         try {
diff --git a/src/EventLoop/Internal/DeferCallback.php b/src/EventLoop/Internal/DeferCallback.php
index b2bd843..21041ae 100644
--- a/src/EventLoop/Internal/DeferCallback.php
+++ b/src/EventLoop/Internal/DeferCallback.php
@@ -9,6 +9,9 @@
 /** @internal */
 final class DeferCallback extends DriverCallback
 {
+    /**
+     * @psalm-pure
+     */
     #[\Override]
     public function getType(): CallbackType
     {
diff --git a/src/EventLoop/Internal/DriverCallback.php b/src/EventLoop/Internal/DriverCallback.php
index 8cb47bf..8e8e492 100644
--- a/src/EventLoop/Internal/DriverCallback.php
+++ b/src/EventLoop/Internal/DriverCallback.php
@@ -23,10 +23,15 @@ public function __construct(
     ) {
     }
 
+    /**
+     * @psalm-capabilities read-props
+     */
     abstract public function getType(): CallbackType;
 
     /**
      * @param string $property
+     *
+     * @psalm-pure
      */
     public function __get(string $property): never
     {
@@ -36,6 +41,8 @@ public function __get(string $property): never
     /**
      * @param string $property
      * @param mixed  $value
+     *
+     * @psalm-pure
      */
     public function __set(string $property, mixed $value): never
     {
diff --git a/src/EventLoop/Internal/DriverSuspension.php b/src/EventLoop/Internal/DriverSuspension.php
index e0edbc7..1b940e3 100644
--- a/src/EventLoop/Internal/DriverSuspension.php
+++ b/src/EventLoop/Internal/DriverSuspension.php
@@ -13,6 +13,8 @@
  *
  * @template T
  * @implements Suspension<T>
+ *
+ * @psalm-suppress ImmutableDependency The driver's bookkeeping and the fibers it runs are not the caller's effects.
  */
 final class DriverSuspension implements Suspension
 {
@@ -179,6 +181,9 @@ public function throw(\Throwable $throwable): void
         }
     }
 
+    /**
+     * @psalm-pure
+     */
     private function formatStacktrace(array $trace): string
     {
         return \implode("\n", \array_map(static function ($e, $i) {
diff --git a/src/EventLoop/Internal/SignalCallback.php b/src/EventLoop/Internal/SignalCallback.php
index 33e02cf..5110cd9 100644
--- a/src/EventLoop/Internal/SignalCallback.php
+++ b/src/EventLoop/Internal/SignalCallback.php
@@ -9,6 +9,9 @@
 /** @internal */
 final class SignalCallback extends DriverCallback
 {
+    /**
+     * @psalm-capabilities read-props
+     */
     public function __construct(
         string $id,
         \Closure $closure,
@@ -17,6 +20,9 @@ public function __construct(
         parent::__construct($id, $closure);
     }
 
+    /**
+     * @psalm-pure
+     */
     #[\Override]
     public function getType(): CallbackType
     {
diff --git a/src/EventLoop/Internal/StreamCallback.php b/src/EventLoop/Internal/StreamCallback.php
index 56a2547..292d20f 100644
--- a/src/EventLoop/Internal/StreamCallback.php
+++ b/src/EventLoop/Internal/StreamCallback.php
@@ -9,6 +9,8 @@ abstract class StreamCallback extends DriverCallback
 {
     /**
      * @param resource $stream
+     *
+     * @psalm-capabilities read-props
      */
     public function __construct(
         string $id,
diff --git a/src/EventLoop/Internal/StreamReadableCallback.php b/src/EventLoop/Internal/StreamReadableCallback.php
index a68c793..39babee 100644
--- a/src/EventLoop/Internal/StreamReadableCallback.php
+++ b/src/EventLoop/Internal/StreamReadableCallback.php
@@ -9,6 +9,9 @@
 /** @internal */
 final class StreamReadableCallback extends StreamCallback
 {
+    /**
+     * @psalm-pure
+     */
     #[\Override]
     public function getType(): CallbackType
     {
diff --git a/src/EventLoop/Internal/StreamWritableCallback.php b/src/EventLoop/Internal/StreamWritableCallback.php
index a3c8626..23c3df8 100644
--- a/src/EventLoop/Internal/StreamWritableCallback.php
+++ b/src/EventLoop/Internal/StreamWritableCallback.php
@@ -9,6 +9,9 @@
 /** @internal */
 final class StreamWritableCallback extends StreamCallback
 {
+    /**
+     * @psalm-pure
+     */
     #[\Override]
     public function getType(): CallbackType
     {
diff --git a/src/EventLoop/Internal/TimerCallback.php b/src/EventLoop/Internal/TimerCallback.php
index 7b6d314..1fcdf5c 100644
--- a/src/EventLoop/Internal/TimerCallback.php
+++ b/src/EventLoop/Internal/TimerCallback.php
@@ -9,6 +9,9 @@
 /** @internal */
 final class TimerCallback extends DriverCallback
 {
+    /**
+     * @psalm-capabilities read-props
+     */
     public function __construct(
         string $id,
         public readonly float $interval,
@@ -19,6 +22,9 @@ public function __construct(
         parent::__construct($id, $callback);
     }
 
+    /**
+     * @psalm-capabilities read-props
+     */
     #[\Override]
     public function getType(): CallbackType
     {
diff --git a/src/EventLoop/Internal/TimerQueue.php b/src/EventLoop/Internal/TimerQueue.php
index 8caef94..b070533 100644
--- a/src/EventLoop/Internal/TimerQueue.php
+++ b/src/EventLoop/Internal/TimerQueue.php
@@ -8,6 +8,8 @@
  * Uses a binary tree stored in an array to implement a heap.
  *
  * @internal
+ *
+ * @psalm-capabilities read-props|write-this-props|write-refs
  */
 final class TimerQueue
 {
@@ -21,6 +23,8 @@ final class TimerQueue
      * Inserts the callback into the queue.
      *
      * Time complexity: O(log(n)).
+     *
+     * @psalm-capabilities read-props|write-this-props|write-refs
      */
     public function insert(TimerCallback $callback): void
     {
@@ -37,6 +41,8 @@ public function insert(TimerCallback $callback): void
      * Removes the given callback from the queue.
      *
      * Time complexity: O(log(n)).
+     *
+     * @psalm-capabilities read-props|write-this-props|write-refs
      */
     public function remove(TimerCallback $callback): void
     {
@@ -57,6 +63,8 @@ public function remove(TimerCallback $callback): void
      * @param float $now Current event loop time.
      *
      * @return TimerCallback|null Expired callback at the top of the heap or null if the callback has not expired.
+     *
+     * @psalm-capabilities read-props|write-this-props|write-refs
      */
     public function extract(float $now): ?TimerCallback
     {
@@ -80,6 +88,8 @@ public function extract(float $now): ?TimerCallback
      * Time complexity: O(1).
      *
      * @return float|null Expiration time of the callback at the top of the heap or null if the heap is empty.
+     *
+     * @psalm-capabilities read-props
      */
     public function peek(): ?float
     {
@@ -88,6 +98,8 @@ public function peek(): ?float
 
     /**
      * @param int $node Rebuild the data array from the given node upward.
+     *
+     * @psalm-capabilities read-props|write-this-props|write-refs
      */
     private function heapifyUp(int $node): void
     {
@@ -100,6 +112,8 @@ private function heapifyUp(int $node): void
 
     /**
      * @param int $node Rebuild the data array from the given node downward.
+     *
+     * @psalm-capabilities read-props|write-this-props|write-refs
      */
     private function heapifyDown(int $node): void
     {
@@ -122,6 +136,9 @@ private function heapifyDown(int $node): void
         }
     }
 
+    /**
+     * @psalm-capabilities read-props|write-this-props|write-refs
+     */
     private function swap(int $left, int $right): void
     {
         $temp = $this->callbacks[$left];
@@ -135,6 +152,8 @@ private function swap(int $left, int $right): void
 
     /**
      * @param int $node Remove the given node and then rebuild the data array.
+     *
+     * @psalm-capabilities read-props|write-this-props|write-refs
      */
     private function removeAndRebuild(int $node): void
     {
diff --git a/src/EventLoop/InvalidCallbackError.php b/src/EventLoop/InvalidCallbackError.php
index 8be00e2..f1ea0e2 100644
--- a/src/EventLoop/InvalidCallbackError.php
+++ b/src/EventLoop/InvalidCallbackError.php
@@ -6,6 +6,11 @@
 
 use Revolt\EventLoop\Internal\ClosureHelper;
 
+/**
+ * Error thrown for an invalid event-loop callback.
+ *
+ * @api
+ */
 final class InvalidCallbackError extends \Error
 {
     public const E_NONNULL_RETURN = 1;
@@ -13,6 +18,8 @@ final class InvalidCallbackError extends \Error
 
     /**
      * MUST be thrown if any callback returns a non-null value.
+     *
+     * @psalm-capabilities read-props
      */
     public static function nonNullReturn(string $callbackId, \Closure $closure): self
     {
@@ -27,6 +34,8 @@ public static function nonNullReturn(string $callbackId, \Closure $closure): sel
      * MUST be thrown if any operation (except disable() and cancel()) is attempted with an invalid callback identifier.
      *
      * An invalid callback identifier is any identifier that is not yet emitted by the driver or cancelled by the user.
+     *
+     * @psalm-pure
      */
     public static function invalidIdentifier(string $callbackId): self
     {
@@ -45,6 +54,8 @@ public static function invalidIdentifier(string $callbackId): self
     /**
      * @param string $callbackId The callback identifier.
      * @param string $message The exception message.
+     *
+     * @psalm-capabilities read-props
      */
     private function __construct(string $callbackId, int $code, string $message)
     {
@@ -62,6 +73,9 @@ public function getCallbackId(): string
         return $this->callbackId;
     }
 
+    /**
+     * @psalm-capabilities read-props|write-this-props|write-refs
+     */
     public function addInfo(string $key, string $message): void
     {
         $this->info[$key] = $message;
diff --git a/src/EventLoop/Suspension.php b/src/EventLoop/Suspension.php
index 216cfc1..5f1886b 100644
--- a/src/EventLoop/Suspension.php
+++ b/src/EventLoop/Suspension.php
@@ -21,11 +21,15 @@
  * ```
  *
  * @template T
+ *
+ * @psalm-mutable
  */
 interface Suspension
 {
     /**
      * @param T $value The value to return from the call to {@see suspend()}.
+     *
+     * @psalm-capabilities io
      */
     public function resume(mixed $value = null): void;
 
@@ -33,11 +37,15 @@ public function resume(mixed $value = null): void;
      * Returns the value provided to {@see resume()} or throws the exception provided to {@see throw()}.
      *
      * @return T
+     *
+     * @psalm-capabilities io
      */
     public function suspend(): mixed;
 
     /**
      * Throws the given exception from the call to {@see suspend()}.
+     *
+     * @psalm-capabilities io
      */
     public function throw(\Throwable $throwable): void;
 }
diff --git a/src/EventLoop/UncaughtThrowable.php b/src/EventLoop/UncaughtThrowable.php
index 2ee4c74..9f9886a 100644
--- a/src/EventLoop/UncaughtThrowable.php
+++ b/src/EventLoop/UncaughtThrowable.php
@@ -8,6 +8,9 @@
 
 final class UncaughtThrowable extends \Error
 {
+    /**
+     * @psalm-pure
+     */
     public static function throwingCallback(\Closure $closure, \Throwable $previous): self
     {
         return new self(
@@ -17,11 +20,17 @@ public static function throwingCallback(\Closure $closure, \Throwable $previous)
         );
     }
 
+    /**
+     * @psalm-pure
+     */
     public static function throwingErrorHandler(\Closure $closure, \Throwable $previous): self
     {
         return new self("Uncaught %s thrown in event loop error handler %s%s", $closure, $previous);
     }
 
+    /**
+     * @psalm-capabilities read-props
+     */
     private function __construct(string $message, \Closure $closure, \Throwable $previous)
     {
         parent::__construct(\sprintf(