diff --git a/server/middleware/constants.go b/server/middleware/constants.go
new file mode 100644
index 0000000..65bee4c
--- /dev/null
+++ b/server/middleware/constants.go
@@ -0,0 +1,8 @@
+package middleware
+
+type contextKey string
+
+const (
+	RequestIDKey contextKey = "request_id"
+	XTestTimeoutKey contextKey = "X-Test-Timeout"
+)
diff --git a/server/middleware/request_id.go b/server/middleware/request_id.go
index f8ed2a0..7521ff1 100644
--- a/server/middleware/request_id.go
+++ b/server/middleware/request_id.go
@@ -8,11 +8,6 @@ import (
 	"github.com/google/uuid"
 )
 
-type contextKey string
-
-// RequestIDKey is the key used to store the request ID in the context.
-const RequestIDKey contextKey = "request_id"
-
 // RequestID middleware adds a unique request ID to the context
 // and sets it in the response header.
 func RequestID(next http.Handler) http.Handler {