diff --git a/packages/web/src/content/docs/custom-tools.mdx b/packages/web/src/content/docs/custom-tools.mdx
index 4586343f0a..d89922b1f8 100644
--- a/packages/web/src/content/docs/custom-tools.mdx
+++ b/packages/web/src/content/docs/custom-tools.mdx
@@ -59,7 +59,7 @@ export const add = tool({
     b: tool.schema.number().describe("Second number"),
   },
   async execute(args) {
-    return args.a + args.b
+    return (args.a + args.b).toString()
   },
 })
 
@@ -70,7 +70,7 @@ export const multiply = tool({
     b: tool.schema.number().describe("Second number"),
   },
   async execute(args) {
-    return args.a * args.b
+    return (args.a * args.b).toString()
   },
 })
 ```