Hey, this is a known issue. It’s the same bug with ToolResult.toJson serialization that’s affecting several users right now. More details are in this thread.
The team is aware. What’s interesting is that you’re seeing this on Codex 5.3 High. Other users mostly reported it on GPT 5.4, and Codex 5.3 seemed to work for them. That’s helpful info.
A couple workarounds that might help:
- Try opening the agent page in Safari (on macOS). Some users said the error doesn’t show up there.
- Try a different model, like GPT 5.4 or Composer 1.5, although based on other reports they might be affected too.
Let me know if any of this helps.