diff --git a/vocabulary/format-assertion/src/main/java/io/github/sebastiantoepfer/jsonschema/vocabulary/formatassertion/Formats.java b/vocabulary/format-assertion/src/main/java/io/github/sebastiantoepfer/jsonschema/vocabulary/formatassertion/Formats.java
index 73c97e9..5e20d89 100644
--- a/vocabulary/format-assertion/src/main/java/io/github/sebastiantoepfer/jsonschema/vocabulary/formatassertion/Formats.java
+++ b/vocabulary/format-assertion/src/main/java/io/github/sebastiantoepfer/jsonschema/vocabulary/formatassertion/Formats.java
@@ -33,6 +33,8 @@
 final class Formats {
 
     private static final Map<String, Map<Integer, String>> RFCS = Map.of(
+        "hostname",
+        Map.of(1123, "hostname"),
         "date-time",
         Map.of(3339, "date-time"),
         "date",
diff --git a/vocabulary/format-assertion/src/main/java/io/github/sebastiantoepfer/jsonschema/vocabulary/formatassertion/rfc/Rfcs.java b/vocabulary/format-assertion/src/main/java/io/github/sebastiantoepfer/jsonschema/vocabulary/formatassertion/rfc/Rfcs.java
index c0266d5..3e2d03a 100644
--- a/vocabulary/format-assertion/src/main/java/io/github/sebastiantoepfer/jsonschema/vocabulary/formatassertion/rfc/Rfcs.java
+++ b/vocabulary/format-assertion/src/main/java/io/github/sebastiantoepfer/jsonschema/vocabulary/formatassertion/rfc/Rfcs.java
@@ -36,6 +36,10 @@ public final class Rfcs {
 
     //create regex with: https://abnf.msweet.org/index.php
     private static final Map<Integer, Map<String, Rule>> RULES = Map.ofEntries(
+        Map.entry(
+            1123,
+            Map.of("hostname", new RegExRule(Pattern.compile("(?=\\A[-a-z0-9]{1,63}\\Z)\\A[a-z0-9]+(-[a-z0-9]+)*\\Z")))
+        ),
         Map.entry(
             2673,
             Map.of("dotted-quad", new RegExRule(Pattern.compile("^\\d{1,3}\\.\\d{1,3}\\.\\d{1,3}\\.\\d{1,3}$")))
diff --git a/vocabulary/format-assertion/src/test/java/io/github/sebastiantoepfer/jsonschema/vocabulary/formatassertion/FormatsTest.java b/vocabulary/format-assertion/src/test/java/io/github/sebastiantoepfer/jsonschema/vocabulary/formatassertion/FormatsTest.java
index 0f299e3..d87993d 100644
--- a/vocabulary/format-assertion/src/test/java/io/github/sebastiantoepfer/jsonschema/vocabulary/formatassertion/FormatsTest.java
+++ b/vocabulary/format-assertion/src/test/java/io/github/sebastiantoepfer/jsonschema/vocabulary/formatassertion/FormatsTest.java
@@ -96,4 +96,10 @@ void should_found_ipv6Format() {
         //ipv4 only -> invalid!
         assertThat(new Formats().findByName("ipv6").applyTo("125.158.4589.1"), is(false));
     }
+
+    @Test
+    void should_found_hostname() {
+        assertThat(new Formats().findByName("hostname").applyTo("www"), is(true));
+        assertThat(new Formats().findByName("hostname").applyTo("bar_baz"), is(false));
+    }
 }