diff --git a/docs/advanced/low-level-server.md b/docs/advanced/low-level-server.md
index b815379ec9..d8aef345eb 100644
--- a/docs/advanced/low-level-server.md
+++ b/docs/advanced/low-level-server.md
@@ -71,6 +71,10 @@ ProtocolError -32603: query.toLowerCase is not a function
 
 `callTool` rejected with a protocol error instead of resolving to an `isError: true` tool result — [Errors](../servers/errors.md) covers the difference.
 
+::: info
+`request.params` is the request parsed with the spec schema, so a member the spec does not define — a `resource_type` next to `name` and `arguments`, say — is dropped before your handler runs.
+:::
+
 ## Validate arguments yourself
 
 From one Zod `inputSchema` the SDK derives the JSON Schema the model sees, validates arguments before your handler runs, and infers the handler's argument types. Here you wrote the JSON Schema by hand, the cast went unchecked, and nothing tied the two together.