diff --git a/3-Domain/src/main/java/link/Link.java b/3-Domain/src/main/java/link/Link.java
new file mode 100644
index 0000000..61c8bf9
--- /dev/null
+++ b/3-Domain/src/main/java/link/Link.java
@@ -0,0 +1,24 @@
+package link;
+
+import category.CategoryId;
+import tag.TagMatcher;
+import user.Username;
+
+import java.util.Set;
+
+public class Link {
+
+	private final LinkId id;
+	private final Username creator;
+	private final LinkUrl url;
+	private final Set<CategoryId> categoryIds;
+	private final Set<TagMatcher> tags;
+
+	public Link(LinkId id, Username creator, LinkUrl url, Set<CategoryId> categoryIds, Set<TagMatcher> tags) {
+		this.id = id;
+		this.creator = creator;
+		this.url = url;
+		this.categoryIds = categoryIds;
+		this.tags = tags;
+	}
+}
diff --git a/3-Domain/src/main/java/link/LinkId.java b/3-Domain/src/main/java/link/LinkId.java
new file mode 100644
index 0000000..682d767
--- /dev/null
+++ b/3-Domain/src/main/java/link/LinkId.java
@@ -0,0 +1,5 @@
+package link;
+
+public record LinkId(int id) {
+
+}
diff --git a/3-Domain/src/main/java/link/LinkUrl.java b/3-Domain/src/main/java/link/LinkUrl.java
new file mode 100644
index 0000000..0d191e9
--- /dev/null
+++ b/3-Domain/src/main/java/link/LinkUrl.java
@@ -0,0 +1,29 @@
+package link;
+
+import exeptions.IllegalValueObjectArgument;
+
+import java.net.MalformedURLException;
+import java.net.URL;
+
+public class LinkUrl {
+
+	private final URL url;
+
+	public LinkUrl(String urlString) throws IllegalValueObjectArgument {
+		try {
+			this.url = new URL(urlString);
+		}
+		catch (MalformedURLException e) {
+			throw new IllegalValueObjectArgument(e.getMessage());
+		}
+	}
+
+	public URL getUrl() {
+		return url;
+	}
+
+	@Override
+	public String toString() {
+		return url.toString();
+	}
+}
diff --git a/3-Domain/src/main/java/link/OnlineCheck.java b/3-Domain/src/main/java/link/OnlineCheck.java
new file mode 100644
index 0000000..0a3e7b7
--- /dev/null
+++ b/3-Domain/src/main/java/link/OnlineCheck.java
@@ -0,0 +1,25 @@
+package link;
+
+import java.io.IOException;
+import java.net.HttpURLConnection;
+
+public class OnlineCheck {
+
+	static Boolean of(LinkUrl url) {
+		int responseCode = getResponseCode(url);
+		return (responseCode < 400 || responseCode == 401 || responseCode == 403);
+	}
+
+	private static int getResponseCode(LinkUrl url) {
+		try {
+			HttpURLConnection http = (HttpURLConnection) url.getUrl().openConnection();
+			http.setRequestMethod("HEAD");
+			http.disconnect();
+
+			return http.getResponseCode();
+		}
+		catch (IOException e) {
+			return 500; //TODO: seems smelly
+		}
+	}
+}
diff --git a/3-Domain/src/test/java/link/LinkUrlTest.java b/3-Domain/src/test/java/link/LinkUrlTest.java
new file mode 100644
index 0000000..1f7443b
--- /dev/null
+++ b/3-Domain/src/test/java/link/LinkUrlTest.java
@@ -0,0 +1,29 @@
+package link;
+
+import exeptions.IllegalValueObjectArgument;
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertDoesNotThrow;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+
+class LinkUrlTest {
+
+	@Test
+	void constructorWorks() {
+		assertDoesNotThrow(() -> new LinkUrl("https://tea.filefighter.de/qvalentin/LinkDitch"));
+	}
+
+	@Test
+	void constructorThrows() {
+		assertThrows(IllegalValueObjectArgument.class, () -> new LinkUrl("tea.filefighter.de/qvalentin/LinkDitch"));
+	}
+
+	@Test
+	void testToString() throws IllegalValueObjectArgument {
+		String urlString = "https://tea.filefighter.de/qvalentin/LinkDitch";
+		LinkUrl sut = new LinkUrl(urlString);
+
+		assertEquals(urlString, sut.toString());
+	}
+}