diff --git a/apps/server/src/mcp/toolkits/preview/tools.test.ts b/apps/server/src/mcp/toolkits/preview/tools.test.ts
index d00ff459b9d..652c20e6ac0 100644
--- a/apps/server/src/mcp/toolkits/preview/tools.test.ts
+++ b/apps/server/src/mcp/toolkits/preview/tools.test.ts
@@ -12,6 +12,19 @@ const schemaHasDescription = (schema: unknown): boolean => {
     .some((members) => members.some(schemaHasDescription));
 };
 
+const schemaHasMultipleAllOfDescriptions = (schema: unknown): boolean => {
+  if (!schema || typeof schema !== "object") return false;
+  const record = schema as Record<string, unknown>;
+  const allOf = Array.isArray(record.allOf) ? record.allOf : [];
+  const descriptionCount = allOf.filter(
+    (member) =>
+      member !== null &&
+      typeof member === "object" &&
+      typeof (member as Record<string, unknown>).description === "string",
+  ).length;
+  return descriptionCount > 1 || Object.values(record).some(schemaHasMultipleAllOfDescriptions);
+};
+
 it("exports provider-compatible object schemas with described parameters", () => {
   for (const tool of Object.values(PreviewToolkit.tools)) {
     const schema = Tool.getJsonSchema(tool) as {
@@ -27,6 +40,9 @@ it("exports provider-compatible object schemas with described parameters", () =>
     expect(schema.type, `${tool.name} must export a top-level object schema`).toBe("object");
     expect(schema.anyOf, `${tool.name} must not export a root anyOf`).toBeUndefined();
     expect(schema.oneOf, `${tool.name} must not export a root oneOf`).toBeUndefined();
+    if (tool.name === "preview_navigate") {
+      expect(schemaHasMultipleAllOfDescriptions(schema)).toBe(false);
+    }
     expect(
       schema.properties?.tabId,
       `${tool.name} must allow an explicit collaborative browser tab target`,
diff --git a/packages/contracts/src/previewAutomation.ts b/packages/contracts/src/previewAutomation.ts
index d89c4d6f66e..e33615fa4c0 100644
--- a/packages/contracts/src/previewAutomation.ts
+++ b/packages/contracts/src/previewAutomation.ts
@@ -12,13 +12,10 @@ import {
 import { ProviderInstanceId } from "./providerInstance.ts";
 
 const BoundedUrl = Schema.String.check(Schema.isTrimmed())
-  .check(
-    Schema.isNonEmpty({
-      description:
-        "Absolute http(s) URL or a schemeless host such as t3.chat or localhost:5173. Schemeless public hosts use https; loopback hosts use http.",
-    }),
-  )
+  .check(Schema.isNonEmpty())
   .check(Schema.isMaxLength(2048));
+const URL_GUIDANCE =
+  "Absolute http(s) URL or a schemeless host such as t3.chat or localhost:5173. Schemeless public hosts use https; loopback hosts use http.";
 const OptionalTimeoutMs = Schema.optional(
   Schema.Int.check(Schema.isGreaterThan(0))
     .check(Schema.isLessThanOrEqualTo(60_000))
@@ -83,8 +80,7 @@ export type PreviewAutomationStatus = typeof PreviewAutomationStatus.Type;
 export const PreviewAutomationOpenInput = Schema.Struct({
   ...PreviewAutomationTabTargetFields,
   url: Schema.optional(BoundedUrl).annotate({
-    description:
-      "Optional initial page URL, for example https://t3.chat or localhost:5173. Omit to open a blank tab.",
+    description: `Optional initial page URL. ${URL_GUIDANCE} Omit to open a blank tab.`,
   }),
   open: Schema.optional(
     Schema.Boolean.annotate({
@@ -124,7 +120,7 @@ export const BrowserNavigationTarget = Schema.Union([
       description: "Selects direct URL navigation.",
     }),
     url: BoundedUrl.annotate({
-      description: "Direct website URL.",
+      description: `Direct website URL. ${URL_GUIDANCE}`,
     }),
   }),
   Schema.Struct({
@@ -151,8 +147,7 @@ export type BrowserNavigationTarget = typeof BrowserNavigationTarget.Type;
 export const PreviewAutomationNavigateInput = Schema.Struct({
   ...PreviewAutomationTabTargetFields,
   url: Schema.optional(BoundedUrl).annotate({
-    description:
-      "Website URL, for example https://t3.chat. Use this for public pages and directly reachable URLs.",
+    description: `Website URL. ${URL_GUIDANCE} Use this for public pages and directly reachable URLs.`,
   }),
   target: Schema.optional(
     BrowserNavigationTarget.annotate({