diff --git a/src/plugin/tools.ts b/src/plugin/tools.ts
index 83f95b4..372bce9 100644
--- a/src/plugin/tools.ts
+++ b/src/plugin/tools.ts
@@ -40,6 +40,10 @@ export function sanitizeFunctionParameters(params: any): any {
     )
       continue;
     const val = params[key];
+    // GigaChat API only accepts format "date", "date-time" or "time".
+    // Other JSON Schema formats (e.g. "uri" used by webfetch) cause 422.
+    if (key === "format" && !["date", "date-time", "time"].includes(val))
+      continue;
     if (key === "properties" && val !== null && typeof val === "object") {
       out[key] = {};
       for (const propKey of Object.keys(val)) {
diff --git a/src/plugin/translation.test.ts b/src/plugin/translation.test.ts
index 44d6fa4..be51267 100644
--- a/src/plugin/translation.test.ts
+++ b/src/plugin/translation.test.ts
@@ -22,6 +22,28 @@ describe("GigaChat Request Translator", () => {
     expect(stringifyArguments(null)).toBe("{}");
   });
 
+  it("drops unsupported JSON Schema format values (422 guard) but keeps date/time", () => {
+    expect(
+      sanitizeFunctionParameters({
+        type: "object",
+        properties: {
+          url: { type: "string", format: "uri" },
+          created: { type: "string", format: "date-time" },
+          day: { type: "string", format: "date" },
+          clock: { type: "string", format: "time" },
+        },
+      }),
+    ).toEqual({
+      type: "object",
+      properties: {
+        url: { type: "string" },
+        created: { type: "string", format: "date-time" },
+        day: { type: "string", format: "date" },
+        clock: { type: "string", format: "time" },
+      },
+    });
+  });
+
   it("rejects an upload response without a usable file ID", async () => {
     const post = vi.spyOn(axios, "post").mockResolvedValue({ data: {} });
     try {