diff --git a/Cargo.lock b/Cargo.lock
index fdbb8b8..fe92ba9 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -11,7 +11,7 @@ dependencies = [
 
 [[package]]
 name = "always_equal"
-version = "1.0.1"
+version = "1.0.2"
 
 [[package]]
 name = "ansi_term"
diff --git a/crates/ptth_server/README.md b/crates/ptth_server/README.md
new file mode 100644
index 0000000..0e82509
--- /dev/null
+++ b/crates/ptth_server/README.md
@@ -0,0 +1,31 @@
+# PTTH Server
+
+The PTTH server is an HTTP server that can serve files from
+behind a firewall, because it only makes outgoing HTTP connections
+to a PTTH relay.
+
+```
+View from outside the PTTH tunnel:
+
+* HTTP client
+|
+|   HTTP(S) requests
+V
+* ptth_relay
+^
+|   HTTP(S) requests
+|
+* ptth_server
+
+View from inside the PTTH tunnel:
+
+* HTTP client
+|
+|   HTTP(S) requests
+V
+* ptth_relay
+|
+|   HTTP(S) requests
+V
+* ptth_server
+```
diff --git a/crates/ptth_server/src/lib.rs b/crates/ptth_server/src/lib.rs
index 94b60a1..10ef157 100644
--- a/crates/ptth_server/src/lib.rs
+++ b/crates/ptth_server/src/lib.rs
@@ -1,8 +1,34 @@
 //! # PTTH Server
 //! 
-//! The PTTH server makes outgoing HTTP connections to a
-//! PTTH relay, and then serves incoming HTTP requests through
-//! the relay.
+//! The PTTH server is an HTTP server that can serve files from
+//! behind a firewall, because it only makes outgoing HTTP connections
+//! to a PTTH relay.
+//! 
+//! ```
+//! View from outside the PTTH tunnel:
+//! 
+//! * HTTP client
+//! |
+//! |   HTTP(S) requests
+//! V
+//! * ptth_relay
+//! ^
+//! |   HTTP(S) requests
+//! |
+//! * ptth_server
+//! 
+//! View from inside the PTTH tunnel:
+//! 
+//! * HTTP client
+//! |
+//! |   HTTP(S) requests
+//! V
+//! * ptth_relay
+//! |
+//! |   HTTP(S) requests
+//! V
+//! * ptth_server
+//! ```
 
 #![warn (clippy::pedantic)]