diff --git a/packages/opencode/src/tool/write.ts b/packages/opencode/src/tool/write.ts
index 6b8fd3dd1..8b69aa2af 100644
--- a/packages/opencode/src/tool/write.ts
+++ b/packages/opencode/src/tool/write.ts
@@ -17,7 +17,25 @@ 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((val) => {
+        if (typeof val === "string") {
+          return val
+        }
+        if (Array.isArray(val)) {
+          // Join array elements with newlines
+          // Handle edge cases: null/undefined -> "", objects -> JSON.stringify, others -> String
+          return val
+            .map((item) => {
+              if (item === null || item === undefined) return ""
+              if (typeof item === "object") return JSON.stringify(item)
+              return String(item)
+            })
+            .join("\n")
+        }
+        return String(val)
+      }, 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) {