diff --git a/open-sse/translator/request/openai-responses.ts b/open-sse/translator/request/openai-responses.ts
index 822229b984..6e6347b765 100644
--- a/open-sse/translator/request/openai-responses.ts
+++ b/open-sse/translator/request/openai-responses.ts
@@ -381,10 +381,18 @@ export function openaiResponsesToOpenAIRequest(
             },
           };
         }
+        // Responses API "hosted" tools (e.g. Codex's request_user_input,
+        // { type: "request_user_input" }) carry no explicit `name` and cannot be
+        // represented as a Chat Completions function declaration. Emitting them with
+        // an empty name produces an anonymous functionDeclaration that downstream
+        // providers such as Gemini reject with a 400 ("Invalid function name").
+        // Skip any tool without a non-empty string name; named tools are unaffected.
+        const name = tool.name;
+        if (typeof name !== "string" || name.trim() === "") return [];
         return {
           type: "function",
           function: {
-            name: toString(tool.name),
+            name,
             description: toString(tool.description),
             parameters: tool.parameters,
             strict: tool.strict,
diff --git a/tests/unit/responses-nameless-hosted-tool-filter.test.ts b/tests/unit/responses-nameless-hosted-tool-filter.test.ts
new file mode 100644
index 0000000000..fba04a5634
--- /dev/null
+++ b/tests/unit/responses-nameless-hosted-tool-filter.test.ts
@@ -0,0 +1,66 @@
+import test from "node:test";
+import assert from "node:assert/strict";
+
+// Regression for port-from-9router#222: the Responses API supports "hosted" tools
+// that carry no explicit `name` field. The Responses->Chat catch-all branch emitted
+// `name: toString(tool.name)`, and `toString(undefined)` returns "", producing an
+// anonymous functionDeclaration. After the OpenAI->Gemini step Gemini rejected the
+// whole request with a 400:
+//   "...function_declarations[N].name: Invalid function name."
+// (OmniRoute already throws for *unknown* hosted tool types up front, but a
+// whitelisted-type tool — function/custom/command — that arrives without a name
+// still fell through the catch-all and produced `name: ""`.)
+// Fix: skip any Responses tool that reaches the catch-all without a non-empty
+// string name; named tools are unaffected.
+const { openaiResponsesToOpenAIRequest } = await import(
+  "../../open-sse/translator/request/openai-responses.ts"
+);
+
+test("#222: a Responses tool reaching the catch-all without a name is dropped, not emitted nameless", () => {
+  const body = {
+    input: [{ type: "message", role: "user", content: [{ type: "input_text", text: "hi" }] }],
+    tools: [
+      {
+        // Named function tool — must survive.
+        type: "function",
+        name: "read_file",
+        description: "Read a file",
+        parameters: { type: "object", properties: { path: { type: "string" } } },
+      },
+      {
+        // Whitelisted "custom" hosted tool with no `name` — passes the up-front
+        // validation guard, then reaches the catch-all. Must be filtered out
+        // rather than emitted with name: "".
+        type: "custom",
+      },
+    ],
+  };
+
+  const out = openaiResponsesToOpenAIRequest("gemini-2.5-pro", body, false, {}) as {
+    tools: { type: string; function: { name: string } }[];
+  };
+
+  // Only the named tool survives; the nameless hosted tool is gone.
+  const names = out.tools.map((t) => t.function?.name).sort();
+  assert.deepEqual(names, ["read_file"]);
+
+  // No tool may carry an empty/undefined name — the exact bug Gemini rejected.
+  assert.equal(
+    out.tools.some((t) => !t.function?.name || t.function.name.trim() === ""),
+    false,
+    "no nameless functionDeclaration must be emitted"
+  );
+});
+
+test("#222: a function-type Responses tool with a whitespace-only name is also dropped", () => {
+  const body = {
+    input: [{ type: "message", role: "user", content: [{ type: "input_text", text: "hi" }] }],
+    tools: [{ type: "function", name: "   " }],
+  };
+
+  const out = openaiResponsesToOpenAIRequest("gemini-2.5-pro", body, false, {}) as {
+    tools: unknown[];
+  };
+
+  assert.equal(out.tools.length, 0, "a whitespace-only name yields no tools");
+});