diff --git a/Services/Website/README.md b/Services/Website/README.md
index 5e356a7..9255e62 100644
--- a/Services/Website/README.md
+++ b/Services/Website/README.md
@@ -138,6 +138,11 @@ Redirecting collapses the `http://` and `https://` copies of every page onto one
 
 `docker-compose.yml` enables it for production; `docker-compose.override.yml` pins it off for local development.
 
+Trailing slashes are canonicalized separately and unconditionally, with no configuration key: the router matches `/mr-rock` and `/mr-rock/` alike, so
+every `GET`/`HEAD` whose path ends in a slash is answered with a `301` to the form without one (`//` collapses to `/`; `/` is left alone). The
+`Location` is relative, so it keeps the request's own scheme and host. Other methods pass through, since a client may repeat a redirected `POST` as a
+`GET` and drop the body.
+
 ### Logging
 | Config key | Environment variable | Default | Description |
 | --- | --- | --- | --- |