Network Issues Guide

Technical Writer, Chrome DevTools & Lighthouse

Google Developer Expert for Web Technology

This guide shows you how to detect network issues or optimization opportunities in the Network panel of Chrome DevTools.

See Get Started to learn the basics of the Network panel.

Queued or stalled requests

Symptoms

Six requests are downloading simultaneously. After that, a series of requests are queued or stalled. Once one of the first six requests finishes, one of the requests in the queue starts.

An example of a queued or stalled series in the Network panel. — **Figure 1**. An example of a queued or stalled series of requests in the Network panel. In the **Waterfall**, you can see that the first six requests for `logo-1024px.png` start simultaneously. The subsequent requests are stalled until one of the original six finishes.

Causes

Too many requests are being made on a single domain. On HTTP/1.0 or HTTP/1.1 connections, Chrome allows a maximum of six simultaneous TCP connections per host.

Fixes

Implement domain sharding if you must use HTTP/1.0 or HTTP/1.1.
Use HTTP/2. Don't use domain sharding with HTTP/2.
Remove or defer unnecessary requests so that critical requests can download earlier.

Slow Time To First Byte (TTFB)

Symptoms

A request spends a long time waiting to receive the first byte from the server.

**Figure 2**. An example of a request with a slow Time To First Byte. The long, green bar in the **Waterfall** indicates that the `wait` request was waiting a long time.

Causes

The connection between the client and server is slow.
The server is slow to respond. Host the server locally to determine if it's the connection or server that is slow. If you still get a slow TTFB when service locally, then the server is slow.

Fixes

If the connection is slow, consider hosting your content on a CDN or changing hosting providers.
If the server is slow, consider optimizing database queries, implementing a cache, or modifying your server configuration.

Slow content download

Symptoms

A request takes a long time to download.

**Figure 3**. An example of a request that takes a long time to download. The long, blue bar in the **Waterfall** next to `elements-panel.png` means it took a long time to download.

Causes

The connection between the client and server is slow.
A lot of content is being downloaded.

Fixes

Consider hosting your content on a CDN or changing hosting providers.
Send fewer bytes by optimizing your requests.

Contribute knowledge

Got a network issue that should be added to this guide?

Send a tweet to @ChromeDevTools.
Start a mailing list thread by emailing google-chrome-developer-tools@googlegroups.com.
Open an issue on the docs repo.

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