diff --git a/.contractual/changesets/add-microchip-field.md b/.contractual/changesets/add-microchip-field.md
new file mode 100644
index 0000000..107f87d
--- /dev/null
+++ b/.contractual/changesets/add-microchip-field.md
@@ -0,0 +1,7 @@
+---
+"petstore": minor
+---
+
+## petstore
+
+- **[minor]** add optional microchipId field to Pet schema for tracking pet microchips
diff --git a/specs/petstore.openapi.yaml b/specs/petstore.openapi.yaml
index 1ee263a..eabc2e7 100644
--- a/specs/petstore.openapi.yaml
+++ b/specs/petstore.openapi.yaml
@@ -140,6 +140,10 @@ components:
           type: number
           minimum: 0
           description: Weight of the pet in kilograms (optional)
+        microchipId:
+          type: string
+          pattern: '^[0-9]{15}$'
+          description: 15-digit microchip ID (optional)
         status:
           type: string
           enum: