diff --git a/src/types/kind.rs b/src/types/kind.rs
new file mode 100644
index 0000000..4f47b85
--- /dev/null
+++ b/src/types/kind.rs
@@ -0,0 +1,28 @@
+use std::fmt;
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord)]
+pub struct Kind(pub u16);
+
+impl fmt::Display for Kind {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "{}", self.0)
+    }
+}
+
+impl Kind {
+    // Some kinds a relay may need to treat differently
+    pub const SEAL: u16 = 13;
+    pub const DM_CHAT: u16 = 14;
+
+    pub fn is_replaceable(&self) -> bool {
+        (10000..20000).contains(&self.0) || self.0 == 0 || self.0 == 3
+    }
+
+    pub fn is_ephemeral(&self) -> bool {
+        (20000..30000).contains(&self.0)
+    }
+
+    pub fn is_parameterized_replaceable(&self) -> bool {
+        (30000..40000).contains(&self.0)
+    }
+}
diff --git a/src/types/mod.rs b/src/types/mod.rs
index 19febd5..03b0ed3 100644
--- a/src/types/mod.rs
+++ b/src/types/mod.rs
@@ -1,2 +1,5 @@
 mod id;
 pub use id::Id;
+
+mod kind;
+pub use kind::Kind;