diff --git a/.changeset/sour-gorillas-smoke.md b/.changeset/sour-gorillas-smoke.md
new file mode 100644
index 000000000..44ba13402
--- /dev/null
+++ b/.changeset/sour-gorillas-smoke.md
@@ -0,0 +1,5 @@
+---
+"deepagents": patch
+---
+
+fix(deepagents): handle non-string content blocks in tool result sizechecking
diff --git a/libs/deepagents/src/middleware/fs.test.ts b/libs/deepagents/src/middleware/fs.test.ts
index 98b0e853f..6d68fefb0 100644
--- a/libs/deepagents/src/middleware/fs.test.ts
+++ b/libs/deepagents/src/middleware/fs.test.ts
@@ -795,6 +795,97 @@ describe("createFilesystemMiddleware", () => {
         expect(result.content).toBe(largeContent);
       }
     });
+
+    it("should evict large array-based content blocks", async () => {
+      const mockBackend = createMockBackend();
+      const mockWrite = vi.fn().mockResolvedValue({
+        error: null,
+        filesUpdate: {
+          "/large_tool_results/test-id": {
+            content: ["large content"],
+            created_at: "2024-01-01T00:00:00Z",
+            modified_at: "2024-01-01T00:00:00Z",
+          },
+        },
+      });
+      mockBackend.write = mockWrite;
+
+      const middleware = createFilesystemMiddleware({
+        backend: mockBackend,
+        toolTokenLimitBeforeEvict: 100,
+      });
+
+      const largeText = "x".repeat(100 * NUM_CHARS_PER_TOKEN + 1000);
+      const mockMessage = new ToolMessage({
+        content: [
+          { type: "text", text: largeText },
+          { type: "text", text: " extra" },
+        ],
+        tool_call_id: "test-id",
+        name: "some_tool",
+      });
+      const mockHandler = vi.fn().mockResolvedValue(mockMessage);
+      const request = {
+        toolCall: { id: "test-id", name: "some_tool" },
+        state: {},
+        config: {},
+      };
+
+      const result = await middleware.wrapToolCall!(
+        request as any,
+        mockHandler,
+      );
+
+      expect(mockWrite).toHaveBeenCalledWith(
+        "/large_tool_results/test-id",
+        largeText + " extra",
+      );
+
+      expect(isCommand(result)).toBe(true);
+      if (isCommand(result)) {
+        const update = result.update as any;
+        expect(update.messages).toHaveLength(1);
+        const truncatedMsg = update.messages[0];
+        expect(truncatedMsg.content).toContain("Tool result too large");
+        expect(truncatedMsg.content).toContain("/large_tool_results/test-id");
+        expect(truncatedMsg.tool_call_id).toBe("test-id");
+      }
+    });
+
+    it("should not evict small array-based content blocks", async () => {
+      const middleware = createFilesystemMiddleware({
+        backend: createMockBackend(),
+        toolTokenLimitBeforeEvict: 1000,
+      });
+
+      const mockMessage = new ToolMessage({
+        content: [
+          { type: "text", text: "small result" },
+          { type: "text", text: " part two" },
+        ],
+        tool_call_id: "test-id",
+        name: "some_tool",
+      });
+      const mockHandler = vi.fn().mockResolvedValue(mockMessage);
+      const request = {
+        toolCall: { id: "test-id", name: "some_tool" },
+        state: {},
+        config: {},
+      };
+
+      const result = await middleware.wrapToolCall!(
+        request as any,
+        mockHandler,
+      );
+
+      expect(ToolMessage.isInstance(result)).toBe(true);
+      if (ToolMessage.isInstance(result)) {
+        expect(result.content).toEqual([
+          { type: "text", text: "small result" },
+          { type: "text", text: " part two" },
+        ]);
+      }
+    });
   });
 
   describe("tools", () => {
diff --git a/libs/deepagents/src/middleware/fs.ts b/libs/deepagents/src/middleware/fs.ts
index c8d0baa9e..73989e894 100644
--- a/libs/deepagents/src/middleware/fs.ts
+++ b/libs/deepagents/src/middleware/fs.ts
@@ -871,9 +871,10 @@ export function createFilesystemMiddleware(
         msg: ToolMessage,
         toolTokenLimitBeforeEvict: number,
       ) {
+        const textContent = msg.text;
         if (
-          typeof msg.content === "string" &&
-          msg.content.length > toolTokenLimitBeforeEvict * NUM_CHARS_PER_TOKEN
+          textContent.length >
+          toolTokenLimitBeforeEvict * NUM_CHARS_PER_TOKEN
         ) {
           // Build StateAndStore from request
           const stateAndStore: StateAndStore = {
@@ -889,7 +890,7 @@ export function createFilesystemMiddleware(
 
           const writeResult = await resolvedBackend.write(
             evictPath,
-            msg.content,
+            textContent,
           );
 
           if (writeResult.error) {
@@ -897,7 +898,7 @@ export function createFilesystemMiddleware(
           }
 
           // Create preview showing head and tail of the result
-          const contentSample = createContentPreview(msg.content);
+          const contentSample = createContentPreview(textContent);
           const replacementText = TOO_LARGE_TOOL_MSG.replace(
             "{tool_call_id}",
             msg.tool_call_id,