diff --git a/.contractual/changesets/add-vaccinated-field.md b/.contractual/changesets/add-vaccinated-field.md
new file mode 100644
index 0000000..75a42c4
--- /dev/null
+++ b/.contractual/changesets/add-vaccinated-field.md
@@ -0,0 +1,7 @@
+---
+"petstore": minor
+---
+
+## petstore
+
+- **[minor]** add optional vaccinated field to track pet vaccination status
diff --git a/specs/petstore.openapi.yaml b/specs/petstore.openapi.yaml
index eabc2e7..660fe9d 100644
--- a/specs/petstore.openapi.yaml
+++ b/specs/petstore.openapi.yaml
@@ -144,6 +144,9 @@ components:
           type: string
           pattern: '^[0-9]{15}$'
           description: 15-digit microchip ID (optional)
+        vaccinated:
+          type: boolean
+          description: Whether the pet is vaccinated (optional)
         status:
           type: string
           enum: