diff --git a/packages/opencode/src/tool/write.ts b/packages/opencode/src/tool/write.ts
index 8c1e53ccaf3a..017838110947 100644
--- a/packages/opencode/src/tool/write.ts
+++ b/packages/opencode/src/tool/write.ts
@@ -19,7 +19,12 @@ const MAX_PROJECT_DIAGNOSTICS_FILES = 5
 export const WriteTool = Tool.define("write", {
   description: DESCRIPTION,
   parameters: z.object({
-    content: z.string().describe("The content to write to the file"),
+    content: z
+      .preprocess(
+        (v) => (typeof v === "object" && v !== null ? JSON.stringify(v, null, 2) : v),
+        z.string(),
+      )
+      .describe("The content to write to the file"),
     filePath: z.string().describe("The absolute path to the file to write (must be absolute, not relative)"),
   }),
   async execute(params, ctx) {