diff --git a/src/CacheInterface.php b/src/CacheInterface.php
index fd5f2d5..844f64f 100644
--- a/src/CacheInterface.php
+++ b/src/CacheInterface.php
@@ -2,12 +2,43 @@
 
 namespace React\Cache;
 
+use Exception;
+use React\Promise\PromiseInterface;
+
+/**
+ * All methods only reject with an exception when an error occurs on the underlying storage
+ * layer, for example the connection with Redis dropped and cannot be recovered, or the
+ * directory on the filesystem used to store cache has the wrong permissions of is full.
+ */
 interface CacheInterface
 {
-    // @return React\Promise\PromiseInterface
+    /**
+     * Fetch an item from the cache, returns a promise which resolves to the value in the
+     * cache on success, resolves with null when the item cannot be found, or rejects
+     * with an exception on error.
+     *
+     * @param string $key
+     * @return PromiseInterface<mixed|null|Exception>
+     */
     public function get($key);
 
+    /**
+     * Store an item in the cache, returns a promise which resolves to true on success or
+     * rejects with an exception on error.
+     *
+     * @param string $key
+     * @param mixed $value
+     * @return PromiseInterface<bool|Exception>
+     */
     public function set($key, $value);
 
+    /**
+     * Remove an item from the cache, returns a promise which resolves to true on success or
+     * rejects with an exception on error. When the $key isn't found in the cache it also
+     * resolves true.
+     *
+     * @param string $key
+     * @return PromiseInterface<bool|Exception>
+     */
     public function remove($key);
 }