diff --git a/packages/opencode/src/tool/tool.ts b/packages/opencode/src/tool/tool.ts
index 91fbb178..eae14414 100644
--- a/packages/opencode/src/tool/tool.ts
+++ b/packages/opencode/src/tool/tool.ts
@@ -7,7 +7,7 @@ export namespace Tool {
   export type Context<M extends Metadata = Metadata> = {
     sessionID: string
     messageID: string
-    toolCallID: string
+    toolCallID?: string
     abort: AbortSignal
     metadata(input: { title?: string; metadata?: M }): void
   }