diff --git a/composer.json b/composer.json
index a520e7d..f307a84 100644
--- a/composer.json
+++ b/composer.json
@@ -19,7 +19,7 @@
     },
     "extra": {
         "branch-alias": {
-            "dev-master": "2.0.x-dev"
+            "dev-master": "3.0.x-dev"
         }
     }
 }
diff --git a/src/CacheInterface.php b/src/CacheInterface.php
index cb05d2f..671e340 100644
--- a/src/CacheInterface.php
+++ b/src/CacheInterface.php
@@ -15,7 +15,7 @@ interface CacheInterface
      * @throws \Psr\SimpleCache\InvalidArgumentException
      *   MUST be thrown if the $key string is not a legal value.
      */
-    public function get(string $key, mixed $default = null);
+    public function get(string $key, mixed $default = null): mixed;
 
     /**
      * Persists data in the cache, uniquely referenced by a key with an optional expiration TTL time.
@@ -31,7 +31,7 @@ public function get(string $key, mixed $default = null);
      * @throws \Psr\SimpleCache\InvalidArgumentException
      *   MUST be thrown if the $key string is not a legal value.
      */
-    public function set(string $key, mixed $value, null|int|\DateInterval $ttl = null);
+    public function set(string $key, mixed $value, null|int|\DateInterval $ttl = null): bool;
 
     /**
      * Delete an item from the cache by its unique key.
@@ -43,14 +43,14 @@ public function set(string $key, mixed $value, null|int|\DateInterval $ttl = nul
      * @throws \Psr\SimpleCache\InvalidArgumentException
      *   MUST be thrown if the $key string is not a legal value.
      */
-    public function delete(string $key);
+    public function delete(string $key): bool;
 
     /**
      * Wipes clean the entire cache's keys.
      *
      * @return bool True on success and false on failure.
      */
-    public function clear();
+    public function clear(): bool;
 
     /**
      * Obtains multiple cache items by their unique keys.
@@ -64,7 +64,7 @@ public function clear();
      *   MUST be thrown if $keys is neither an array nor a Traversable,
      *   or if any of the $keys are not a legal value.
      */
-    public function getMultiple(iterable $keys, mixed $default = null);
+    public function getMultiple(iterable $keys, mixed $default = null): iterable;
 
     /**
      * Persists a set of key => value pairs in the cache, with an optional TTL.
@@ -80,7 +80,7 @@ public function getMultiple(iterable $keys, mixed $default = null);
      *   MUST be thrown if $values is neither an array nor a Traversable,
      *   or if any of the $values are not a legal value.
      */
-    public function setMultiple(iterable $values, null|int|\DateInterval $ttl = null);
+    public function setMultiple(iterable $values, null|int|\DateInterval $ttl = null): bool;
 
     /**
      * Deletes multiple cache items in a single operation.
@@ -93,7 +93,7 @@ public function setMultiple(iterable $values, null|int|\DateInterval $ttl = null
      *   MUST be thrown if $keys is neither an array nor a Traversable,
      *   or if any of the $keys are not a legal value.
      */
-    public function deleteMultiple(iterable $keys);
+    public function deleteMultiple(iterable $keys): bool;
 
     /**
      * Determines whether an item is present in the cache.
@@ -110,5 +110,5 @@ public function deleteMultiple(iterable $keys);
      * @throws \Psr\SimpleCache\InvalidArgumentException
      *   MUST be thrown if the $key string is not a legal value.
      */
-    public function has(string $key);
+    public function has(string $key): bool;
 }