W3C mobileOK Checker

If you're wondering what the mobileOK Checker is and what it does, the About page should provide some answers.

The tests performed by the W3C mobileOK Checker are formally defined in the W3C mobileOK Basic Tests 1.0 standard and are based on a subset of the Mobile Web Best Practices 1.0 standard.

The tests cover different areas that impact the mobile-friendliness of Web content:

• Markup validation: some tags and attributes that may be used in a page may not be well supported by a vast majority of mobile devices.
• Structure of the page: size matters on mobile devices, using tables for layout usually does not work, support for Javascript is limited, pop-ups and frames negatively impact the user experience on small screens
• CSS style sheets: using absolute measures is unlikely to work well on mobile devices
• Images/Objects: image format and dimensions should match the capabilities of the device.
• User input: default values should be provided in input fields whenever possible, user inputs should be minimized.
• HTTP level: proper caching and encoding information should be sent in the HTTP header.
• Character encoding: is the content properly encoded in UTF-8?
• Links: content targetted by the page should be appropriate for mobile devices.

Being mobileOK is neither a guarantee that the Web document may be rendered correctly by all mobile devices, nor an insurance that the user experience was correctly addressed. Further quality improvements based on the full set of the Mobile Web Best Practices may be in order. Please check the Mobile Web Best Practices Flipcards for a quick overview of the Mobile Web Best Practices!

Similarly, some parts of the page may not be parsed and checked if they do not have an impact on most mobile devices. For instance, CSS styles that do not apply to the handheld media type are ignored (see CSS Style in the W3C mobileOK Basic Tests 1.0 standard). Javascript files are not taken into account either when computing the size of the page because many mobile devices simply do not support Javascript and will not retrieve the file.

Sure! If you have a question, a suggestion, want to contribute, wonder how to author mobile-friendly content, or if you find a bug, do tell us!

The Feedback page explains how to get in touch with us.

Yes, the checks include a markup validation similar to the one performed by the Markup Validation Service. However, in the case of the mobileOK Checker, the validation is not made against the doctype declared in the page, but against the XHTML Basic 1.1 DTD. Markup validation errors returned by the mobileOK Checker are not detailed. For a more detailed response, please use the Markup Validation Service.

The About page details the origins of the mobileOK Checker. In practice, the Checker is composed of the User Interface maintained by W3C staff, based on an open-source mobileOK Checker library maintained by the Checker Task Force of the W3C Mobile Web Best Practices Working Group.

Simply paste the address of the page you would like to check into the text area on the checker's home page, and press the "Check" button.

The Mobile Web Best Practices standard is composed of 60 best pratices. To help summarize and understand the areas that are impacted, the failure messages are grouped into 10 categories. These categories represent 10 different ways to mobilize one's content. The categories are:

• Design for One Web
• Rely on Web standards
• Stay away from known hazards
• Be cautious of device limitations
• Optimize navigation
• Check graphics & colors
• Keep it small
• Use the network sparingly
• Help & guide user input
• Think of users on the go

Check the Mobile Web Best Practices flipcards for more information.

The score between 0 and 100 that appears near the top of mobileOK reports is computed based on the number and severity of failures encountered by the mobileOK Checker while running the tests on the page. The score measures the level of mobile-friendliness of the page. While we try our best to make the score be as meaningfull as possible, it should be read with care as it is not completely absolute. A page that scores 90/100 may appear broken on more mobile devices than a page that scores 70/100. Severity levels and costs are being adjusted over time based on experience. Let us know if you think the score of a given page is wrong!

The score should rather be read as an incentive to improve your page so that they render well on a vast majority of mobile devices. Fix a failure, and watch your score increase!

Each failure is given a severity level between 1 (low) and 6 (critical). Each severity level costs a given number of points. For example, a medium failure costs 5 points. The final score is 100 minus the sum of the costs of the failures. The sum of the costs may exceed 100, in which case the report will simply report that This page is not mobile-friendly!

A few rules are applied that adjust the actual cost of a failure:

• When a failure occurs more than once, the cost contributed by the additional occurrences is dampened following an inverse rule so that the total cost for a given failure stays reasonable.
• The cost contributed by the size of the page depends on the actual size. The bigger the page, the higher the cost.
• Similarly, the cost contributed by the number of embedded resources in the page depends on the number of exceeding resources (mobileOK sets 20 as the limit).
• The total cost of failures with a severe, medium or low severity cannot exceed 50.

Warnings do not cost anything as they do not necessarily mean that something needs to be fixed (see What is (are) this (these) warning message(s)?).

Size matters when delivering content on mobile devices, both because of the usual limited bandwidth of mobile networks and because of the limited capacities of some mobile devices in terms of memory or caching storage. The size represents the total number of bytes that would be retrieved by a mobile browser to render the page. It includes the size of the page itself, the size of the images embedded in the page, the size of the CSS style sheet(s) that the page uses, and also includes the size of potential intermediate redirections that may be needed to retrieve the page.

Please note that the total does not include resources that would not be retrieved by most mobile devices. In particular, the total does not include the size of external CSS style sheets that do not apply to the handheld media type. Similarly, the total does not include the size of potential external Javascript files.

Provided your browser supports Javascript, details per resource are available if you expand the section. When redirections are used, the size of the redirection messages is included in the total and displayed in a separate column. Redirections do have a cost in the mobile world!

The number of requests that appears below the global score represents the number of HTTP round trips that a mobile browser would need to render the page. Each round trip has an associated "cost" in the case of mobile devices, because of the high latency of typical mobile networks. The number of requests is detailed per component of the page: the page itself, the images, the CSS style sheets.

Provided your browser supports Javascript, details per resource are available if you expand the section. A resource may account for more than one request when more than one HTTP round trip is needed to retrieve it, in other words when redirections are used. Redirections do have a cost in the mobile world!

As for the size of the page, please note that the total does not include resources that would not be retrieved by most mobile devices. In particular, the total does not include external CSS style sheets that do not apply to the handheld media type. Similarly, the total does not include potential external Javascript files.

Failures are reported whenever a test does not pass. A failure means that something in the page, in the way the page is delivered on the Web, or in the resources embedded in the page negatively impacts the mobile-friendliness of the page and should be fixed. Fixing failures directly improves the user experience of the page on a mobile device.

The number and severity of failures is used to compute the global score of the page. Each time a failure is fixed, the score improves!

Each failure message comes with a clear explanation of the failure, why it's important to fix it, and how this can usually be done. If you think a message is obscure, feel free to send your feedback!

Failures are formerly defined in the W3C mobileOK Basic Tests 1.0 standard.

The main goal of the warnings is to alert authors on points that may have an impact on the user experience on mobile devices and that may be worth checking. As opposed to failures, warnings do not necessarily mean that something needs to be fixed in the page. For example, a vast majority of mobile devices support tables, but large tables may not render well on mobile devices. Thus, tables trigger a warning that basically says "By the way, I noticed the presence of a table in the page. Have you considered the possibility to linearize the table so that it renders neatly even on small screens?"

Warnings do not contribute to the global score of the page. Warnings may still be returned in mobileOK pages.

Warnings are formerly defined in the W3C mobileOK Basic Tests 1.0 standard.

Some failures have a very negative impact on the mobile-friendliness of the page. Others only slightly affect the overall experience of the page on mobile devices. We understand that Web authors only have limited time available to fix failures, and may prefer to focus on the most severe ones. Each failure thus comes with a severity level:

• critical: Most mobile devices will not be able to render (part of) the page or will not be able to render the page in a reasonable time frame. Critical failures should be addressed first!
• severe: Most mobile devices should render the page but the user experience is strongly impacted.
• medium: A mobile constraint has not been taken into account or the page relies on implicit hypotheses that could turn out to be wrong. For instance, a more conservative use of the network is possible (e.g. whitespaces account for more than 10% of the size of the page) or the character encoding is not explicitly set in the page.
• low: useful improvements are possible.
• warning: A warning alerts authors on a point that may have an impact on the user experience on mobile devices and that may be worth checking. A warning does not necessarily mean that something needs to be fixed in the page. Warnings do not affect the score of the page.
• info: An informational message is a lightweight warning that alerts authors on a point that may have an impact on the user experience on mobile devices if it is not handled with care. For instance, using scripting is not discouraged but authors should check that the page remains usable without scripting. Informational messages do not affect the score of the page.

If the mobileOK Checker returns a signification number of failures, and if you are among the authors of the Web page checked by the mobileOK Checker, you might be wondering what you should start looking at to improve the mobile-friendliness of your page. Most severe failures are listed first, so you should simply start with the failures that appear at the beginning of the list.