diff --git a/README.rst b/README.rst
index ca13015..2f0eba7 100644
--- a/README.rst
+++ b/README.rst
@@ -15,7 +15,8 @@ Two way to create a new appliance:
 After that you can send us a pull request on Github.
 
 
-In schemas/appliance.json you have a JSON with a schema for controlling the file.
+In schemas/appliance.json you have a JSON with a schema for controlling the file
+and can be use as documentation for each fields.
 
 
 Tools
diff --git a/schemas/appliance.json b/schemas/appliance.json
index 25cab53..60adfdb 100644
--- a/schemas/appliance.json
+++ b/schemas/appliance.json
@@ -78,7 +78,7 @@
     },
     "port_segment_size": {
         "type": "integer",
-        "title": "Optional port segment size"
+        "title": "Optional port segment size. A port segment is a block of port. For example Ethernet0/0 Ethernet0/1 is the module 0 with a port segment size of 2"
     },
 
     "qemu": {