diff --git a/schema/index.yaml b/schema/index.yaml
index ed1b0de..15c7ecd 100644
--- a/schema/index.yaml
+++ b/schema/index.yaml
@@ -116,6 +116,7 @@ $defs:
         type: string
       caption:
         type: string
+        pattern: '^((([A-Za-z]{3,9}:(?:\/\/)?)(?:[-;:&=\+\$,\w]+@)?[A-Za-z0-9.-]+|(?:www.|[-;:&=\+\$,\w]+@)[A-Za-z0-9.-]+)((?:\/[\+~%\/.\w-_]*)?\??(?:[-\+=&;%@.\w_]*)#?(?:[\w]*))?)'
       country:
         type: string
         pattern: '^[a-z]{2}$'
@@ -214,4 +215,4 @@ properties:
   research:
     type: array
     items:
-      $ref: "#/$defs/research"
\ No newline at end of file
+      $ref: "#/$defs/research"