Merge pull request #223 from langchain-ai/fix-write-file

fix(deepagents): prevent write_file crash when model omits content

Author: maahir30

.changeset/happy-flowers-mix.md

@@ -0,0 +1,6 @@
+---
+"deepagents": patch
+---
+
+fix(deepagents): prevent write_file crash when model omits content
+- Default the content parameter to an empty string so a missing argument doesn't crash the entire agent run via Zod validation failure.

libs/deepagents/src/middleware/fs.test.ts

@@ -727,4 +727,22 @@ describe("createFilesystemMiddleware", () => {
       }
     });
   });
+
+  describe("tools", () => {
+    it("write_file schema should accept missing content and default to empty string", () => {
+      const middleware = createFilesystemMiddleware({
+        backend: createMockBackend(),
+      });
+
+      const writeFileTool = middleware.tools!.find(
+        (t: any) => t.name === "write_file",
+      ) as any;
+      expect(writeFileTool).toBeDefined();
+
+      // Parse with only file_path, no content — simulates the model omitting it
+      const parsed = writeFileTool.schema.parse({ file_path: "/app/test.c" });
+      expect(parsed.file_path).toBe("/app/test.c");
+      expect(parsed.content).toBe("");
+    });
+  });
 });

libs/deepagents/src/middleware/fs.ts

@@ -522,7 +522,10 @@ function createWriteFileTool(
       description: customDescription || WRITE_FILE_TOOL_DESCRIPTION,
       schema: z.object({
         file_path: z.string().describe("Absolute path to the file to write"),
-        content: z.string().describe("Content to write to the file"),
+        content: z
+          .string()
+          .default("")
+          .describe("Content to write to the file"),
       }),
     },
   );