diff --git a/composer.json b/composer.json
index e4c224d..9f350de 100644
--- a/composer.json
+++ b/composer.json
@@ -15,6 +15,12 @@
 		"psalm:check": "psalm.phar --threads=1 --no-cache --show-info=true",
 		"psalm:fix": "psalm.phar --no-cache --alter --issues=InvalidReturnType,InvalidNullableReturnType,MissingParamType,InvalidFalsableReturnType"
 	},
+	"autoload": {
+		"psr-4": {
+			"OCA\\RePod\\": "lib/",
+			"OCA\\GPodderSync\\": "stubs/OCA/GPodderSync/"
+		}
+	},
 	"config": {
 		"platform": {
 			"php": "8.0"
diff --git a/psalm.xml b/psalm.xml
index bacd293..70602d3 100644
--- a/psalm.xml
+++ b/psalm.xml
@@ -10,6 +10,7 @@
 >
 	<projectFiles>
 		<directory name="lib" />
+		<directory name="stubs" />
 		<ignoreFiles>
 			<directory name="vendor" />
 		</ignoreFiles>
diff --git a/stubs/OCA/GPodderSync/Core/EpisodeAction/EpisodeAction.php b/stubs/OCA/GPodderSync/Core/EpisodeAction/EpisodeAction.php
new file mode 100644
index 0000000..0029ed4
--- /dev/null
+++ b/stubs/OCA/GPodderSync/Core/EpisodeAction/EpisodeAction.php
@@ -0,0 +1,44 @@
+<?php
+
+declare(strict_types=1);
+
+namespace OCA\GPodderSync\Core\EpisodeAction;
+
+/**
+ * @psalm-type EpisodeActionType = array{
+ *  podcast: string,
+ *  episode: string,
+ *  action: string,
+ *  timestamp: string,
+ *  started: int,
+ *  position: int,
+ *  total: int,
+ *  guid: ?string,
+ *  id: int
+ * }
+ */
+interface EpisodeAction
+{
+	public function getPodcast(): string;
+
+	public function getEpisode(): string;
+
+	public function getAction(): string;
+
+	public function getTimestamp(): string;
+
+	public function getStarted(): int;
+
+	public function getPosition(): int;
+
+	public function getTotal(): int;
+
+	public function getGuid(): ?string;
+
+	public function getId(): int;
+
+	/**
+	 * @return EpisodeActionType
+	 */
+	public function toArray(): array;
+}
diff --git a/stubs/OCA/GPodderSync/Core/EpisodeAction/EpisodeActionReader.php b/stubs/OCA/GPodderSync/Core/EpisodeAction/EpisodeActionReader.php
new file mode 100644
index 0000000..403a071
--- /dev/null
+++ b/stubs/OCA/GPodderSync/Core/EpisodeAction/EpisodeActionReader.php
@@ -0,0 +1,15 @@
+<?php
+
+declare(strict_types=1);
+
+namespace OCA\GPodderSync\Core\EpisodeAction;
+
+interface EpisodeActionReader
+{
+	/**
+	 * @param  array                     $episodeActionsArray []
+	 * @return EpisodeAction[]
+	 * @throws \InvalidArgumentException
+	 */
+	public function fromArray(array $episodeActionsArray): array;
+}
diff --git a/stubs/OCA/GPodderSync/Core/EpisodeAction/EpisodeActionSaver.php b/stubs/OCA/GPodderSync/Core/EpisodeAction/EpisodeActionSaver.php
new file mode 100644
index 0000000..b0da7a6
--- /dev/null
+++ b/stubs/OCA/GPodderSync/Core/EpisodeAction/EpisodeActionSaver.php
@@ -0,0 +1,10 @@
+<?php
+
+declare(strict_types=1);
+
+namespace OCA\GPodderSync\Core\EpisodeAction;
+
+interface EpisodeActionSaver
+{
+	public function saveEpisodeActions(array $episodeActionsArray, string $userId): array;
+}
diff --git a/stubs/OCA/GPodderSync/Core/PodcastData/PodcastActionCounts.php b/stubs/OCA/GPodderSync/Core/PodcastData/PodcastActionCounts.php
new file mode 100644
index 0000000..5a261f0
--- /dev/null
+++ b/stubs/OCA/GPodderSync/Core/PodcastData/PodcastActionCounts.php
@@ -0,0 +1,29 @@
+<?php
+
+declare(strict_types=1);
+
+namespace OCA\GPodderSync\Core\PodcastData;
+
+/**
+ * @psalm-type PodcastActionCountsType = array{
+ *  delete: int,
+ *  download: int,
+ *  flattr: int,
+ *  new: int,
+ *  play: int
+ * }
+ */
+interface PodcastActionCounts extends \JsonSerializable
+{
+	public function incrementAction(string $action): void;
+
+	/**
+	 * @return PodcastActionCountsType
+	 */
+	public function toArray(): array;
+
+	/**
+	 * @return PodcastActionCountsType
+	 */
+	public function jsonSerialize(): array;
+}
diff --git a/stubs/OCA/GPodderSync/Core/PodcastData/PodcastData.php b/stubs/OCA/GPodderSync/Core/PodcastData/PodcastData.php
new file mode 100644
index 0000000..db27f8c
--- /dev/null
+++ b/stubs/OCA/GPodderSync/Core/PodcastData/PodcastData.php
@@ -0,0 +1,57 @@
+<?php
+
+declare(strict_types=1);
+
+namespace OCA\GPodderSync\Core\PodcastData;
+
+/**
+ * @psalm-type PodcastDataType = array{
+ *  title: ?string,
+ *  author: ?string,
+ *  link: ?string,
+ *  description: ?string,
+ *  imageUrl: ?string,
+ *  fetchedAtUnix: int,
+ *  imageBlob: ?string
+ * }
+ */
+interface PodcastData extends \JsonSerializable
+{
+	public function __toString(): string;
+
+	/**
+	 * @throws \Exception if the XML data could not be parsed
+	 */
+	public static function parseRssXml(string $xmlString, ?int $fetchedAtUnix = null): PodcastData;
+
+	public function getTitle(): ?string;
+
+	public function getAuthor(): ?string;
+
+	public function getLink(): ?string;
+
+	public function getDescription(): ?string;
+
+	public function getImageUrl(): ?string;
+
+	public function getFetchedAtUnix(): ?int;
+
+	public function getImageBlob(): ?string;
+
+	public function setImageBlob(?string $blob): void;
+
+	/**
+	 * @return PodcastDataType
+	 */
+	public function toArray(): array;
+
+	/**
+	 * @return PodcastDataType
+	 */
+	public function jsonSerialize(): array;
+
+	/**
+	 * @param PodcastDataType $data
+	 */
+	public static function fromArray(array $data): PodcastData;
+}
diff --git a/stubs/OCA/GPodderSync/Core/PodcastData/PodcastDataReader.php b/stubs/OCA/GPodderSync/Core/PodcastData/PodcastDataReader.php
new file mode 100644
index 0000000..06f6dbf
--- /dev/null
+++ b/stubs/OCA/GPodderSync/Core/PodcastData/PodcastDataReader.php
@@ -0,0 +1,16 @@
+<?php
+
+declare(strict_types=1);
+
+namespace OCA\GPodderSync\Core\PodcastData;
+
+interface PodcastDataReader
+{
+	public function getCachedOrFetchPodcastData(string $url, string $userId): ?PodcastData;
+
+	public function fetchPodcastData(string $url, string $userId): ?PodcastData;
+
+	public function tryGetCachedPodcastData(string $url): ?PodcastData;
+
+	public function trySetCachedPodcastData(string $url, PodcastData $data): bool;
+}
diff --git a/stubs/OCA/GPodderSync/Core/PodcastData/PodcastMetrics.php b/stubs/OCA/GPodderSync/Core/PodcastData/PodcastMetrics.php
new file mode 100644
index 0000000..db2ded6
--- /dev/null
+++ b/stubs/OCA/GPodderSync/Core/PodcastData/PodcastMetrics.php
@@ -0,0 +1,33 @@
+<?php
+
+declare(strict_types=1);
+
+namespace OCA\GPodderSync\Core\PodcastData;
+
+/**
+ * @psalm-type PodcastMetricsType = array{
+ *  url: string,
+ *  listenedSeconds: int,
+ *  actionCounts: PodcastActionCounts
+ * }
+ */
+interface PodcastMetrics extends \JsonSerializable
+{
+	public function getUrl(): string;
+
+	public function getActionCounts(): PodcastActionCounts;
+
+	public function getListenedSeconds(): int;
+
+	public function addListenedSeconds(int $seconds): void;
+
+	/**
+	 * @return PodcastMetricsType
+	 */
+	public function toArray(): array;
+
+	/**
+	 * @return PodcastMetricsType
+	 */
+	public function jsonSerialize(): array;
+}
diff --git a/stubs/OCA/GPodderSync/Core/PodcastData/PodcastMetricsReader.php b/stubs/OCA/GPodderSync/Core/PodcastData/PodcastMetricsReader.php
new file mode 100644
index 0000000..0cceba1
--- /dev/null
+++ b/stubs/OCA/GPodderSync/Core/PodcastData/PodcastMetricsReader.php
@@ -0,0 +1,13 @@
+<?php
+
+declare(strict_types=1);
+
+namespace OCA\GPodderSync\Core\PodcastData;
+
+interface PodcastMetricsReader
+{
+	/**
+	 * @return PodcastMetrics[]
+	 */
+	public function metrics(string $userId): array;
+}
diff --git a/stubs/OCA/GPodderSync/Core/SubscriptionChange/SubscriptionChange.php b/stubs/OCA/GPodderSync/Core/SubscriptionChange/SubscriptionChange.php
new file mode 100644
index 0000000..9a9d480
--- /dev/null
+++ b/stubs/OCA/GPodderSync/Core/SubscriptionChange/SubscriptionChange.php
@@ -0,0 +1,14 @@
+<?php
+
+declare(strict_types=1);
+
+namespace OCA\GPodderSync\Core\SubscriptionChange;
+
+interface SubscriptionChange
+{
+	public function __toString(): string;
+
+	public function isSubscribed(): bool;
+
+	public function getUrl(): string;
+}
diff --git a/stubs/OCA/GPodderSync/Core/SubscriptionChange/SubscriptionChangeRequestParser.php b/stubs/OCA/GPodderSync/Core/SubscriptionChange/SubscriptionChangeRequestParser.php
new file mode 100644
index 0000000..f41edde
--- /dev/null
+++ b/stubs/OCA/GPodderSync/Core/SubscriptionChange/SubscriptionChangeRequestParser.php
@@ -0,0 +1,13 @@
+<?php
+
+declare(strict_types=1);
+
+namespace OCA\GPodderSync\Core\SubscriptionChange;
+
+interface SubscriptionChangeRequestParser
+{
+	/**
+	 * @return SubscriptionChange[]
+	 */
+	public function createSubscriptionChangeList(array $urlsSubscribed, array $urlsUnsubscribed): array;
+}
diff --git a/stubs/OCA/GPodderSync/Core/SubscriptionChange/SubscriptionChangeSaver.php b/stubs/OCA/GPodderSync/Core/SubscriptionChange/SubscriptionChangeSaver.php
new file mode 100644
index 0000000..7720d92
--- /dev/null
+++ b/stubs/OCA/GPodderSync/Core/SubscriptionChange/SubscriptionChangeSaver.php
@@ -0,0 +1,10 @@
+<?php
+
+declare(strict_types=1);
+
+namespace OCA\GPodderSync\Core\SubscriptionChange;
+
+interface SubscriptionChangeSaver
+{
+	public function saveSubscriptionChanges(array $urlsSubscribed, array $urlsUnsubscribed, string $userId): void;
+}
diff --git a/stubs/OCA/GPodderSync/Core/SubscriptionChange/SubscriptionChangesReader.php b/stubs/OCA/GPodderSync/Core/SubscriptionChange/SubscriptionChangesReader.php
new file mode 100644
index 0000000..4b833ad
--- /dev/null
+++ b/stubs/OCA/GPodderSync/Core/SubscriptionChange/SubscriptionChangesReader.php
@@ -0,0 +1,13 @@
+<?php
+
+declare(strict_types=1);
+
+namespace OCA\GPodderSync\Core\SubscriptionChange;
+
+interface SubscriptionChangesReader
+{
+	/**
+	 * @return SubscriptionChange[]
+	 */
+	public static function mapToSubscriptionsChanges(array $urls, bool $subscribed): array;
+}