diff --git a/open-sse/config/toolCloaking.ts b/open-sse/config/toolCloaking.ts
index 429a6ca28bcb..22f648eabb5b 100644
--- a/open-sse/config/toolCloaking.ts
+++ b/open-sse/config/toolCloaking.ts
@@ -52,6 +52,40 @@ function toToolName(value: unknown): string {
   return typeof value === "string" ? value.trim() : "";
 }
 
+/**
+ * Recursively strip `enumDescriptions` from a JSON schema.
+ *
+ * VSCode Copilot emits `enumDescriptions` inside tool parameter schemas, but the
+ * Antigravity API rejects any request carrying that field with HTTP 400. Walk the
+ * schema's `properties` and `items` so the field is removed at every nesting level
+ * before the declaration is sent upstream.
+ */
+export function stripEnumDescriptions(schema: unknown): unknown {
+  if (!schema || typeof schema !== "object") return schema;
+
+  if (Array.isArray(schema)) {
+    return schema.map((entry) => stripEnumDescriptions(entry));
+  }
+
+  const result: JsonRecord = { ...(schema as JsonRecord) };
+  delete result.enumDescriptions;
+
+  const properties = asRecord(result.properties);
+  if (properties) {
+    const nextProperties: JsonRecord = {};
+    for (const key of Object.keys(properties)) {
+      nextProperties[key] = stripEnumDescriptions(properties[key]);
+    }
+    result.properties = nextProperties;
+  }
+
+  if (result.items !== undefined) {
+    result.items = stripEnumDescriptions(result.items);
+  }
+
+  return result;
+}
+
 export function shouldCloakAntigravityTool(toolName: string): boolean {
   return (
     toolName.length > 0 && !AG_DEFAULT_TOOLS.has(toolName) && !toolName.endsWith(AG_TOOL_SUFFIX)
@@ -99,9 +133,20 @@ export function cloakAntigravityToolPayload<T extends JsonRecord>(
         const declaration = asRecord(declarationValue);
         if (!declaration) continue;
 
-        const rawName = toToolName(declaration.name);
+        // VSCode Copilot sends `enumDescriptions` in tool parameter schemas, but the
+        // Antigravity API rejects requests carrying that field with HTTP 400. Strip it
+        // recursively before the declaration is forwarded upstream.
+        const stripped: JsonRecord =
+          declaration.parameters !== undefined
+            ? { ...declaration, parameters: stripEnumDescriptions(declaration.parameters) }
+            : declaration;
+        if (stripped !== declaration) {
+          changed = true;
+        }
+
+        const rawName = toToolName(stripped.name);
         if (!rawName) {
-          cloakedDeclarations.push({ ...declaration });
+          cloakedDeclarations.push({ ...stripped });
           continue;
         }
 
@@ -112,7 +157,7 @@ export function cloakAntigravityToolPayload<T extends JsonRecord>(
         }
 
         cloakedDeclarations.push({
-          ...declaration,
+          ...stripped,
           name: cloakedName,
         });
       }
diff --git a/tests/unit/antigravity-tool-cloaking.test.ts b/tests/unit/antigravity-tool-cloaking.test.ts
index cf413718e478..3770eab655f8 100644
--- a/tests/unit/antigravity-tool-cloaking.test.ts
+++ b/tests/unit/antigravity-tool-cloaking.test.ts
@@ -5,6 +5,7 @@ import {
   AG_DECOY_TOOLS,
   AG_TOOL_SUFFIX,
   cloakAntigravityToolPayload,
+  stripEnumDescriptions,
 } from "../../open-sse/config/toolCloaking.ts";
 
 test("cloakAntigravityToolPayload cloaks custom tools, preserves native tools and injects decoys", () => {
@@ -92,3 +93,101 @@ test("cloakAntigravityToolPayload composes namespace sanitization maps with Anti
     "mcp__filesystem__workspace_read"
   );
 });
+
+test("stripEnumDescriptions removes enumDescriptions at every nesting level", () => {
+  const schema = {
+    type: "OBJECT",
+    enumDescriptions: ["should be removed at root"],
+    properties: {
+      mode: {
+        type: "STRING",
+        enum: ["a", "b"],
+        enumDescriptions: ["desc a", "desc b"],
+      },
+      nested: {
+        type: "OBJECT",
+        properties: {
+          choice: {
+            type: "STRING",
+            enumDescriptions: ["deep desc"],
+          },
+        },
+      },
+      list: {
+        type: "ARRAY",
+        items: {
+          type: "STRING",
+          enumDescriptions: ["item desc"],
+        },
+      },
+    },
+  };
+
+  const stripped = stripEnumDescriptions(schema) as any;
+
+  assert.equal("enumDescriptions" in stripped, false);
+  assert.equal("enumDescriptions" in stripped.properties.mode, false);
+  assert.equal("enumDescriptions" in stripped.properties.nested.properties.choice, false);
+  assert.equal("enumDescriptions" in stripped.properties.list.items, false);
+  // Non-target fields are preserved.
+  assert.deepEqual(stripped.properties.mode.enum, ["a", "b"]);
+  // Input is not mutated.
+  assert.ok(Array.isArray((schema.properties.mode as any).enumDescriptions));
+});
+
+test("cloakAntigravityToolPayload strips enumDescriptions from declaration parameters", () => {
+  const payload = {
+    request: {
+      tools: [
+        {
+          functionDeclarations: [
+            {
+              name: "workspace_read",
+              description: "Read a file",
+              parameters: {
+                type: "OBJECT",
+                enumDescriptions: ["root-level"],
+                properties: {
+                  mode: {
+                    type: "STRING",
+                    enum: ["read", "write"],
+                    enumDescriptions: ["read mode", "write mode"],
+                  },
+                },
+              },
+            },
+            {
+              name: "run_command",
+              description: "Native tool keeps visible name but loses enumDescriptions",
+              parameters: {
+                type: "OBJECT",
+                properties: {
+                  shell: {
+                    type: "STRING",
+                    enumDescriptions: ["bash", "zsh"],
+                  },
+                },
+              },
+            },
+          ],
+        },
+      ],
+      contents: [],
+    },
+  };
+
+  const result = cloakAntigravityToolPayload(payload);
+  const declarations = (result.body.request.tools?.[0] as any)?.functionDeclarations || [];
+
+  const cloaked = declarations.find(
+    (d: { name: string }) => d.name === `workspace_read${AG_TOOL_SUFFIX}`
+  );
+  assert.ok(cloaked, "cloaked client tool present");
+  assert.equal("enumDescriptions" in cloaked.parameters, false);
+  assert.equal("enumDescriptions" in cloaked.parameters.properties.mode, false);
+  assert.deepEqual(cloaked.parameters.properties.mode.enum, ["read", "write"]);
+
+  const native = declarations.find((d: { name: string }) => d.name === "run_command");
+  assert.ok(native, "native tool preserved");
+  assert.equal("enumDescriptions" in native.parameters.properties.shell, false);
+});