diff --git a/admin/dyncookie/dyncookie.c b/admin/dyncookie/dyncookie.c
new file mode 100644
index 0000000..0c778eb
--- /dev/null
+++ b/admin/dyncookie/dyncookie.c
@@ -0,0 +1,55 @@
+/*
+ * Dynamic server cookie calculator
+ *
+ * Copyright 2021 Willy Tarreau <w@1wt.eu>
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version
+ * 2 of the License, or (at your option) any later version.
+ *
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdarg.h>
+#include <arpa/inet.h>
+#include <import/xxhash.h>
+
+__attribute__((noreturn)) void die(int code, const char *format, ...)
+{
+	va_list args;
+
+	va_start(args, format);
+	vfprintf(stderr, format, args);
+	va_end(args);
+	exit(code);
+}
+
+int main(int argc, char **argv)
+{
+	size_t key_len;
+	int addr_len;
+	char *buf;
+	int port;
+
+	if (argc < 4)
+		die(1, "Usage: %s <key> <ip> <port>\n", argv[0]);
+
+	key_len = strlen(argv[1]);
+	buf = realloc(strdup(argv[1]), key_len + 16 + 4);
+	if (!buf)
+		die(2, "Not enough memory\n");
+
+	if (inet_pton(AF_INET, argv[2], buf + key_len) > 0)
+		addr_len = 4;
+	else if (inet_pton(AF_INET6, argv[2], buf + key_len) > 0)
+		addr_len = 16;
+	else
+		die(3, "Cannot parse address <%s> as IPv4/IPv6\n", argv[2]);
+
+	port = htonl(atoi(argv[3]));
+	memcpy(buf + key_len + addr_len, &port, 4);
+	printf("%016llx\n", (long long)XXH64(buf, key_len + addr_len + 4, 0));
+	return 0;
+}