diff --git a/lib/Controller/BoardApiController.php b/lib/Controller/BoardApiController.php
index d7afc6dcc..cc974f083 100644
--- a/lib/Controller/BoardApiController.php
+++ b/lib/Controller/BoardApiController.php
@@ -24,6 +24,7 @@
 
 namespace OCA\Deck\Controller;
 
+use OCA\Deck\Db\Board;
 use OCA\Deck\StatusException;
 use OCP\AppFramework\ApiController;
 use OCP\AppFramework\Http;
@@ -72,7 +73,11 @@ class BoardApiController extends ApiController {
 			}
 			$boards = $this->boardService->findAll($date->getTimestamp(), $details);
 		}
-		return new DataResponse($boards, HTTP::STATUS_OK);
+		$response = new DataResponse($boards, HTTP::STATUS_OK);
+		$response->setETag(md5(json_encode(array_map(function (Board $board) {
+			return $board->getId() . '-' . $board->getETag();
+		}, $boards))));
+		return $response;
 	}
 
 	/**
diff --git a/lib/Db/Label.php b/lib/Db/Label.php
index 830a66d9f..b6e6b414f 100644
--- a/lib/Db/Label.php
+++ b/lib/Db/Label.php
@@ -36,4 +36,8 @@ class Label extends RelationalEntity {
 		$this->addType('cardId', 'integer');
 		$this->addType('lastModified', 'integer');
 	}
+
+	public function getETag() {
+		return md5((string)$this->getLastModified());
+	}
 }
diff --git a/lib/Db/RelationalEntity.php b/lib/Db/RelationalEntity.php
index 5da532daa..7f21a9a7e 100644
--- a/lib/Db/RelationalEntity.php
+++ b/lib/Db/RelationalEntity.php
@@ -80,6 +80,9 @@ class RelationalEntity extends Entity implements \JsonSerializable {
 				$json[$property] = $value;
 			}
 		}
+		if ($reflection->hasMethod('getETag')) {
+			$json['ETag'] = $this->getETag();
+		}
 		return $json;
 	}
 
diff --git a/tests/unit/Db/BoardTest.php b/tests/unit/Db/BoardTest.php
index 369e13a61..e7bef3328 100644
--- a/tests/unit/Db/BoardTest.php
+++ b/tests/unit/Db/BoardTest.php
@@ -32,6 +32,7 @@ class BoardTest extends TestCase {
 			'archived' => false,
 			'users' => ['user1', 'user2'],
 			'settings' => [],
+			'ETag' => $board->getETag(),
 		], $board->jsonSerialize());
 	}
 
@@ -52,6 +53,7 @@ class BoardTest extends TestCase {
 			'archived' => false,
 			'users' => [],
 			'settings' => [],
+			'ETag' => $board->getETag(),
 		], $board->jsonSerialize());
 	}
 	public function testSetAcl() {
@@ -80,6 +82,7 @@ class BoardTest extends TestCase {
 			'shared' => 1,
 			'users' => [],
 			'settings' => [],
+			'ETag' => $board->getETag(),
 		], $board->jsonSerialize());
 	}
 }
diff --git a/tests/unit/Db/CardTest.php b/tests/unit/Db/CardTest.php
index 995ff2d54..01f638a07 100644
--- a/tests/unit/Db/CardTest.php
+++ b/tests/unit/Db/CardTest.php
@@ -84,6 +84,7 @@ class CardTest extends TestCase {
 			'deletedAt' => 0,
 			'commentsUnread' => 0,
 			'lastEditor' => null,
+			'ETag' => $card->getETag(),
 		], $card->jsonSerialize());
 	}
 	public function testJsonSerializeLabels() {
@@ -109,6 +110,7 @@ class CardTest extends TestCase {
 			'deletedAt' => 0,
 			'commentsUnread' => 0,
 			'lastEditor' => null,
+			'ETag' => $card->getETag(),
 		], $card->jsonSerialize());
 	}
 
@@ -144,6 +146,7 @@ class CardTest extends TestCase {
 			'deletedAt' => 0,
 			'commentsUnread' => 0,
 			'lastEditor' => null,
+			'ETag' => $card->getETag(),
 		], $card->jsonSerialize());
 	}
 }
diff --git a/tests/unit/Db/LabelTest.php b/tests/unit/Db/LabelTest.php
index b129c29a3..ee8a370a1 100644
--- a/tests/unit/Db/LabelTest.php
+++ b/tests/unit/Db/LabelTest.php
@@ -42,7 +42,8 @@ class LabelTest extends TestCase {
 			'boardId' => 123,
 			'cardId' => null,
 			'lastModified' => null,
-			'color' => '000000'
+			'color' => '000000',
+			'ETag' => $label->getETag(),
 		], $label->jsonSerialize());
 	}
 	public function testJsonSerializeCard() {
@@ -54,7 +55,8 @@ class LabelTest extends TestCase {
 			'boardId' => null,
 			'cardId' => 123,
 			'lastModified' => null,
-			'color' => '000000'
+			'color' => '000000',
+			'ETag' => $label->getETag(),
 		], $label->jsonSerialize());
 	}
 }
diff --git a/tests/unit/Db/StackTest.php b/tests/unit/Db/StackTest.php
index 76016d555..3ec9688e5 100644
--- a/tests/unit/Db/StackTest.php
+++ b/tests/unit/Db/StackTest.php
@@ -33,7 +33,7 @@ class StackTest extends \Test\TestCase {
 		return $board;
 	}
 	public function testJsonSerialize() {
-		$board = $this->createStack();
+		$stack = $this->createStack();
 		$this->assertEquals([
 			'id' => 1,
 			'title' => "My Stack",
@@ -41,12 +41,13 @@ class StackTest extends \Test\TestCase {
 			'boardId' => 1,
 			'deletedAt' => 0,
 			'lastModified' => 0,
-		], $board->jsonSerialize());
+			'ETag' => $stack->getETag(),
+		], $stack->jsonSerialize());
 	}
 	public function testJsonSerializeWithCards() {
 		$cards = ["foo", "bar"];
-		$board = $this->createStack();
-		$board->setCards($cards);
+		$stack = $this->createStack();
+		$stack->setCards($cards);
 		$this->assertEquals([
 			'id' => 1,
 			'title' => "My Stack",
@@ -55,6 +56,7 @@ class StackTest extends \Test\TestCase {
 			'cards' => ["foo", "bar"],
 			'deletedAt' => 0,
 			'lastModified' => 0,
-		], $board->jsonSerialize());
+			'ETag' => $stack->getETag(),
+		], $stack->jsonSerialize());
 	}
 }
diff --git a/tests/unit/controller/BoardApiControllerTest.php b/tests/unit/controller/BoardApiControllerTest.php
index 1f63acf4f..3fd9198f0 100644
--- a/tests/unit/controller/BoardApiControllerTest.php
+++ b/tests/unit/controller/BoardApiControllerTest.php
@@ -72,7 +72,7 @@ class BoardApiControllerTest extends \Test\TestCase {
 
 		$expected = new DataResponse($boards, HTTP::STATUS_OK);
 		$actual = $this->controller->index();
-
+		$actual->setETag(null);
 		$this->assertEquals($expected, $actual);
 	}
 
@@ -90,6 +90,7 @@ class BoardApiControllerTest extends \Test\TestCase {
 			->will($this->returnValue($boardId));
 
 		$expected = new DataResponse($board, HTTP::STATUS_OK);
+		$expected->setETag($board->getETag());
 		$actual = $this->controller->get();
 		$this->assertEquals($expected, $actual);
 	}
diff --git a/tests/unit/controller/CardApiControllerTest.php b/tests/unit/controller/CardApiControllerTest.php
index e4980a834..4ef894f16 100644
--- a/tests/unit/controller/CardApiControllerTest.php
+++ b/tests/unit/controller/CardApiControllerTest.php
@@ -72,6 +72,7 @@ class CardApiControllerTest extends \Test\TestCase {
 			->willReturn($card);
 
 		$expected = new DataResponse($card, HTTP::STATUS_OK);
+		$expected->setETag($card->getETag());
 		$actual = $this->controller->get();
 		$this->assertEquals($expected, $actual);
 	}
diff --git a/tests/unit/controller/StackApiControllerTest.php b/tests/unit/controller/StackApiControllerTest.php
index 5878e560f..4d30176a9 100644
--- a/tests/unit/controller/StackApiControllerTest.php
+++ b/tests/unit/controller/StackApiControllerTest.php
@@ -78,6 +78,7 @@ class StackApiControllerTest extends \Test\TestCase {
 
 		$expected = new DataResponse($stacks, HTTP::STATUS_OK);
 		$actual = $this->controller->index();
+		$actual->setETag(null);
 		$this->assertEquals($expected, $actual);
 	}
 
@@ -97,6 +98,7 @@ class StackApiControllerTest extends \Test\TestCase {
 			->willReturn($this->exampleStack['id']);
 
 		$expected = new DataResponse($stack, HTTP::STATUS_OK);
+		$expected->setETag($stack->getETag());
 		$actual = $this->controller->get();
 		$this->assertEquals($expected, $actual);
 	}