diff --git a/tests/unit/tools-filter-anthropic-format.test.mjs b/tests/unit/tools-filter-anthropic-format.test.mjs
new file mode 100644
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+++ b/tests/unit/tools-filter-anthropic-format.test.mjs
@@ -0,0 +1,93 @@
+/**
+ * Unit tests for PR #397 — Anthropic-format tools filter fix (#346)
+ *
+ * Verifies that tools arriving in Anthropic format (`tool.name` without `.function`)
+ * are NOT dropped by the empty-name filter in chatCore.ts.
+ * Before the fix, ALL anthropic-format tools were silently dropped, causing
+ * `400: tool_choice.any may only be specified while providing tools` from Anthropic.
+ */
+
+import { describe, it } from "node:test";
+import assert from "node:assert/strict";
+
+// Inline the filter logic from chatCore.ts (lines 225-231 after #397 fix)
+function filterEmptyNameTools(tools) {
+  return tools.filter((tool) => {
+    const fn = tool.function;
+    const name = fn?.name ?? tool.name;
+    return name && String(name).trim().length > 0;
+  });
+}
+
+describe("tools empty-name filter — #346 / PR #397", () => {
+  it("should keep tools with valid OpenAI format name (tool.function.name)", () => {
+    const tools = [
+      { type: "function", function: { name: "get_weather", description: "Get weather" } },
+    ];
+    assert.equal(filterEmptyNameTools(tools).length, 1);
+  });
+
+  it("should keep tools with valid Anthropic format name (tool.name)", () => {
+    const tools = [
+      { name: "get_weather", description: "Get weather", input_schema: { type: "object" } },
+    ];
+    assert.equal(filterEmptyNameTools(tools).length, 1);
+  });
+
+  it("should drop tools with empty OpenAI format name (tool.function.name = '')", () => {
+    const tools = [{ type: "function", function: { name: "" } }];
+    assert.equal(filterEmptyNameTools(tools).length, 0);
+  });
+
+  it("should drop tools with empty Anthropic format name (tool.name = '')", () => {
+    const tools = [{ name: "", description: "Ghost tool", input_schema: { type: "object" } }];
+    assert.equal(filterEmptyNameTools(tools).length, 0);
+  });
+
+  it("should NOT drop Anthropic-format tools when function wrapper is absent (regression for PR #397)", () => {
+    // Before fix: fn was undefined, fn?.name was undefined, filter returned false → ALL tools dropped
+    // After fix: fn?.name ?? tool.name → falls back to tool.name → keeps valid tools
+    const tools = [
+      {
+        name: "search",
+        description: "Search the web",
+        input_schema: { type: "object", properties: {} },
+      },
+      { name: "code_exec", description: "Execute code", input_schema: { type: "object" } },
+    ];
+    const result = filterEmptyNameTools(tools);
+    assert.equal(result.length, 2, "Both anthropic-format tools should be preserved");
+  });
+
+  it("should handle mixed format tools in the same array", () => {
+    const tools = [
+      { type: "function", function: { name: "openai_tool" } }, // OpenAI format
+      { name: "anthropic_tool", input_schema: { type: "object" } }, // Anthropic format
+      { type: "function", function: { name: "" } }, // Empty OpenAI — should be dropped
+      { name: "", input_schema: { type: "object" } }, // Empty Anthropic — should be dropped
+    ];
+    const result = filterEmptyNameTools(tools);
+    assert.equal(result.length, 2, "Should keep 2 valid tools (one of each format)");
+    assert.ok(
+      result.some((t) => t.function?.name === "openai_tool"),
+      "OpenAI tool preserved"
+    );
+    assert.ok(
+      result.some((t) => t.name === "anthropic_tool"),
+      "Anthropic tool preserved"
+    );
+  });
+
+  it("should handle tools with whitespace-only names", () => {
+    const tools = [{ name: "   ", input_schema: { type: "object" } }];
+    assert.equal(filterEmptyNameTools(tools).length, 0);
+  });
+
+  it("should handle null/undefined tool.name gracefully", () => {
+    const tools = [
+      { input_schema: { type: "object" } }, // Neither name nor function
+      { name: null, input_schema: { type: "object" } },
+    ];
+    assert.equal(filterEmptyNameTools(tools).length, 0);
+  });
+});