diff --git a/kernelspec-spec/kernelspec.schema.json b/kernelspec-spec/kernelspec.schema.json
index 8bc21dfd..d959ee5d 100644
--- a/kernelspec-spec/kernelspec.schema.json
+++ b/kernelspec-spec/kernelspec.schema.json
@@ -23,8 +23,9 @@
             "type": "string"
         },
         "kernel_protocol_version": {
-            "description": "The version of protocol this kernel implements. If not specified, the client will assume the version is <5.5 until it can get it via the kernel_info request.",
-            "type": "string"
+            "description": "The version of protocol this kernel implements. If not specified, the client will assume the version is <5.5 until it can get it via the kernel_info request. The kernel protocol uses semantic versioning (SemVer).",
+            "type": "string",
+            "pattern": "^(0|[1-9]\d*)\.(0|[1-9]\d*)\.(0|[1-9]\d*)(?:-((?:0|[1-9]\d*|\d*[a-zA-Z-][0-9a-zA-Z-]*)(?:\.(?:0|[1-9]\d*|\d*[a-zA-Z-][0-9a-zA-Z-]*))*))?(?:\+([0-9a-zA-Z-]+(?:\.[0-9a-zA-Z-]+)*))?$"
         },
         "interrupt_mode": {
             "description": "May be either signal or message and specifies how a client is supposed to interrupt cell execution on this kernel, either by sending an interrupt signal via the operating system’s signalling facilities (e.g. SIGINT on POSIX systems), or by sending an interrupt_request message on the control channel (see Kernel interrupt). If this is not specified the client will default to signal mode.",