hey, 431 errors usually mean your request headers are too big. had this happen before. often it's super large cookies being sent with every request, especially during local dev.
check your browser's dev tools network tab to see what headers are going out. you might need to clear site data for your dev server.
if you're running something like nginx or caddy in front of node, that's where you'd typically increase header buffer limits. for pure node, it's more about what the client is sending.
- check cookies: often the culprit.
- custom headers: too many or too big?
- proxy config: if you use one (like nginx), adjust its header buffer settings.