For invisible frames e.g. ones in background tabs, Chrome set a per-frame simultaneous loading limit; 3 for the top frame, 2 for sub-frames are permitted to go to the network stack. Excessive requests are enqueued and go when the previous request finishes. Thus, all requests will run eventually. Most fetches made by HTML elements / CSS are throttleable. WebSockets, WebRTC's data channel, Fetch API, XMLHttpRequest, EventSource, Video and Audio are excluded today to allow keep-alive connections.

Status in Chromium


Enabled by default (tracking bug)

Consensus & Standardization

After a feature ships in Chrome, the values listed here are not guaranteed to be up to date.

  • No signal
  • No signal
  • No signals



Chrome proactively shows console warnings when requests reach to the limit in each frame, but you can just ignore warnings, and we will omit these messages in later versions. If you notice something actually is wrong, please file a bug at, and set 'Blink>Loader' component label. is open for general discussion. But before posting, please make sure that your problem can be solved if chrome://flags/#enable-resource-load-scheduler is Disabled.

Last updated on 2021-10-10