Avoid HTTP redirects (no-http-redirects)

no-http-redirects checks if there are any HTTP redirects in the page webhint is analyzing.

Why is this important?

Consider the following simplified description of what happens when a user requests a URL within a browser:

1. DNS Lookup: Translate the server domain to an IP. If the browser doesn’t know it, it asks a DNS server which in some cases involves multiple queries until the final IP is obtained.
2. Open a TCP connection to the server IP address requesting the URL.
3. The server responds to that request by sending some content over the TCP connection. If the resource uses SSL, then TLS negotiation(s) happens as well.

When a redirect occurs, 3. contains the new URL the browser needs to request, repeating the whole sequence of steps. DNS Lookup isn’t cheap, neither is creating a TCP connection. The impact of redirects is felt even more by mobile users, where the network latency is usually higher. As a rule of thumb, the more you can avoid redirects the better.

What does the hint check?

This hint checks:

• If the target URL passed to webhint has any redirect. E.g.: http://www.example.com --> http://example.com
• If any resource in the page has any redirect. E.g.: http://example.com/script.js --> https://example.com/script.js

and alerts if at least one is found.

Examples that trigger the hint

• Any URL passed to webhint that redirects to another one
• Any page with a resource (script, css, image) behind a redirect

Examples that pass the hint

• No redirect for resources nor the target URL.

Can the hint be configured?

By default, no redirects are allowed but you can change this behavior.

The following hint configuration used in the .hintrc file will allow 3 redirects for resources and 1 for the main URL:

{
    "connector": {...},
    "formatters": [...],
    "hints": {
        "no-http-redirects": ["error", {
            "max-resource-redirects": 3,
            "max-html-redirects": 1
        }],
        ...
    },
    ...
}

How to use this hint?

This package is installed automatically by webhint:

npm install hint --save-dev

To use it, activate it via the .hintrc configuration file:

{
    "connector": {...},
    "formatters": [...],
    "hints": {
        "no-http-redirects": "error",
        ...
    },
    "parsers": [...],
    ...
}

Note: The recommended way of running webhint is as a devDependency of your project.

Further Reading

• Mobile Analysis in PageSpeed Insights
• 50 performance tricks to make your HTML5 apps and sites faster (skip to 19:35)
• Domain Names - Implementation and Specification
• How DNS Works
• Redirections in HTTP
• Transmission Control Protocol