The web accessibility basics

I’ve been asked again and again over the years what the absolute basics of web accessibility are. And while I always thought that it is not so difficult to find resources about these basics, the recurrence of that question prompted me to finally write my own take on this topic. So here it is, my list of absolute web accessibility basics every web developer should know about.

Alternative text for images

One of the questions I get asked the most is “which graphics require alternative text”? The answer to this question has three parts:

  1. All img tags require an alt attribute. This goes without exception. Everything else is an error. If you have an img tag in your HTML without an alt attribute, add it now.
  2. Every alt attribute has to have a value. And here is where it gets interesting. If the image is important, because it is part of an a tag, for example, it has to have meaningful text. What is a best alt text is still a point of sometimes heated debate, but the guideline is to use best judgement. Describe the image briefly, but avoid the phrase “image of” or “graphic of”. Because screen readers already know it is a graphic. In addition, every image that adds context to the text of a page that is important in understanding the text needs to have meaningful alternative text. If, on the other hand, an image is purely decorative, its alternative text consists of an empty string “”. That is simply alt=””, two consecutive quotes. But the alt attribute has to be there even for these decorative images, it must not be omitted.
  3. It is called alt attribute, alternative text, but never alt tag. alt is an attribute, not a HTML tag.

All the above also applies to SVG graphics. And if you’re really modern and use the picture element, the rules apply there, too.

Using proper alternative text does not just help blind and low vision screen reader users. It also helps on mobile where images sometimes cannot be loaded, for example over slow connections. So by implementing proper alternative text, you help many more people than you might initially imagine.

Labeling form fields

Another very common question I get, and a very common error I see on many many web pages even in 2015, concerns the labeling of forms and form fields. In fact, when dealing with many web developers, I am surprised that many don’t even seem to be aware that there is a label element, for example. So here are the most common rules about form field accessibility:

  1. Most input elements, as well as the select and textarea elements, need an associated label element that states the purpose. The one exception are those that produce a button, like the types of button, reset, and submit do. But every other, be it text, checkbox, password, radio (button), search etc. require a label element to be present.
  2. The association between such an input and label happens by giving the input a unique ID, given by the id attribute on the input, and the label’s for attribute, which points to said ID. To test that your label actually works, click on the label, not the input, select or textarea. Does the said element still get focus? If so, you did things right. This increases the click target for many audiences, including mobile devices where bigger touch targets are always advantageous. And it associates the label text to the input for screen readers unambiguously. Do not, under any circumstances, use the placeholder attribute as the label for an input element! Read here, why.
  3. Give button elements inner text, or if it needs to be a graphic, label it properly with alt text that corresponds to what a textual button label would be. See the section on alternative text for images above. Also, as recommended in the MDN article linked to, prefer button elements over html:input type=”button”, because it is more flexible for styling. Also, this is the go-to element if you have anything that is a div or span and that you want to make clickable with hundreds of kilobytes of JavaScript code. So before you do that, use button instead.
  4. A series of radio buttons go inside a fieldset element to group them together. The first element inside this fieldset is the legend element that contains the over-arching question or label for this group of choices.
  5. Fieldset and Legend should also be used if grouping together different sections of a bigger form for better readability. The fieldset element can take more than just radio button inputs.
  6. Label required fields by providing the HTML5 required attribute on the input as well as stating in the label that a form field is required. This can be done by either providing the word “required” as part of the label, or putting explanatory text at the top of the form telling users that fields marked with an asterisk are required. Do not denote required fields only by a different color. Screen reader users won’t be able to recognize those, and color-blind users, which are 8 percent of the worldwide male population, will also have a hard time finding these.
  7. Use appropriate input types for e-mail, URL, phone number etc. Mobile users will thank you because these will bring up the correct keyboards for the information asked. Also, it will make evaluation easier for you because the browser will immediately know if the correct information, e. g. a valid e-mail address, was entered. Modern browsers will do that, and if you need to support older browsers, they’ll automatically fall back to text, which is an appropriate fall-back.
  8. Make sure keyboard visibility is always guaranteed. If you see a frame appear around a form field when you click inside it, you should also see it appear when you walk through your form using the tab key on your keyboard. If it does not apear, check your :focus and :active stylings for these form fields in your CSS.

If you need something a little more fancy-looking, please do not fall back to using clickable span and div elements. Because if you do that, you’ll have to add roles, state handling, keyboard focusability and acting on key presses all by yourself. If you use form elements and help yourself with some span elements for styling inside the label, for example, you will get all the accessibility for free, including keyboard, screen readers etc.

Document structure

Believe it or not, but at its core, the web is a document-based structure. So even when we create fancy web applications such as Gmail, the heart of it is a document. And there is a lot you can do with documents semantically that will get you usually 80 to 90 percent of the accessibility for free. For example:

Heading structure

Noticed the different headings and sub headings in this blog post? Well, there are elements for that. They are called heading elements. And they give you exactly that, a six level heading structure to denote a main heading, secondary sub headings, and sub headings to those for sub sections, like this one, for example. This gives your document a logical, easy to follow structure. Have you ever wondered how Wikipedia puts together its table of contents for each article? They use the logical heading structure for that, too!The h1 through h6 elements are unambiguous in telling screen readers, search engines and other technologies what the structure of your document is. Do not mix unless the structure requires it, do not skip levels if possible, since that will disrupt the logic. And never ever again use something like a div with a class of “heading1” in your code. Screen readers, search engines, and other technologies will not know what to do with those. They will know how to treat your headings properly, though!


There are some more ways to structure your document’s contents. By landmarks, for example. Landmarks can be article, aside, footer, header, nav and main. Adding such landmarks appropriately can help further provide sense to your document and help users more easily navigate it.


HTML knows a whole bunch about lists. There are unordered and ordered lists that are exactly what you’d expect them to be. You can add numbering schemes, even nest them, and the browser will do the rest for you. You can style them the way you want them to look in CSS and thus provide even more structure and meaning to your document’s content. You’ve already seen ordered (numbered) lists in this blog post.

There is also a list type for definition term and explanation groups. The MDN page on the dl element has some great examples of use.


Did you know that HTML has an element to denote paragraphs? It is called the p element. For long citations that require their own paragraphs, use blockquote. For short, inline, quotes, use the q element. Visual separators can be inserted via the hr element.

For all these elements, use CSS to define indentation, separation between paragraphs etc. Those will not impact the semantics, but you are then free to adjust the visuals to your liking or your client’s requirements.


Tables are its own special case. So much can go wrong, and historically, so much abuse has happened to this poor table element and its sub elements! Especially layouts were done for a long time using tables, before HTML 4 and the onset of CSS. But I still find in modern web applications in 2015, cases where layout tables are being used to align form fields and their labels to one another. STOP DOING THAT! PLEASE!

The table element is a very useful element for creating data representations. Product detail listings, price lists etc. Also, shopping carts with quantities, sub totals and totals, and many other structured data collections can, and should, be put into data tables. Here are some tips to help you:

  1. Add a caption element to give the table a proper heading or summary.
  2. Use th elements to denote column and row headings. Make use of their scope and other attributes to clearly associate what belongs to which.
  3. Use other structural table elements denoted in the “see also” section of the table element documentation to further structure your table.
  4. If a table gets too complex or has multiple sections that don’t necessarily have to be in one table, split them up into several data tables.

For more information, I’d like to refer you to the friends at WebAIM who have put together a very good two-pager on the accessibility of HTML tables.

Some more quickies

Here are some more things you can quickly check and make sure when you write HTML, CSS and JavaScript.

Separation of concepts

HTML defines your content structure. It is what screen readers and other assistive technologies use to represent your content to their users.

CSS defines how that content looks visually. Its positioning, indentation, padding, margins usually have no bearing on what screen readers render to the user, with one exception: If display: none; or visibility: hidden; styles are used, that content will also not be available to assistive technologies. See my post titled “Hiding content untagled” for more information.

Also, CSS :before and :after text is rendered to assistive technologies. So be aware what you put in there.

JavaScript adds dynamic functionality. Its output must be proper HTML and CSS, too, if it manipulates the DOM. JavaScript dynamics in itself are no problem to accessibility, only some specific behaviors can be, like losing keyboard focus.

The clearer you separate the three, the more maintainable your code will be. Put CSS in their own files, don’t embed it in the HTML. Put JS modules in their files and don’t embed JS code in your HTML, either. This will make everything more readable, and remind you that the concepts should really be separate that just happen to work together rather than mingling uncontrollably.

Color contrast

Have you ever stood in the sunlight or another bright light source with your smartphone or tablet in hand and wondered why you couldn’t read something? Well, you were suffering from a lack of contrast between foreground and background on the page you were visiting. Low contrast ratios lead to bad readability in bright light situations. For the aging population, as well as low-vision users, low contrasts pose an even greater obstacle in readability. The Web Content Accessibility Guidelines define as a success criteria to have a contrast ratio of 4.5:1 on main content text to its background. You can use tools like the Colour Contrast Analyser to point at your content and see whether your visuals meet this requirement. Even if you’re not auditing for WCAG compliance, adhering to this rule of thumb is still a good idea for your own eyes as well as everyone else’s.

Keep Pinch alive!

When you develop for the mobile web, and today it is most likely you are, please keep the Pinch To Zoom gesture alive! Do not disable this gesture vital to many more of your readers than you might think! Pinching to zoom something small on a web page is very common and does not apply only to aging readers as well as those with low vision. If your layout does not cope with the pinch gesture for some reason, you need to revisit your responsive design and fix it. Do not disable the pinch gesture on mobile browsers!

OK, but what about advanced widgets?

If you really need to implement advanced widgets that are not indiginous to HTML, take good care that you implement all aspects of them. I have some information on how to make clickable widgets that should be buttons or links, tabs and tabpanels, some auto-complete widgets and modal dialogs accessible. The friends at SSB Bart Group have a quite current post on ARIA tree views up, and Terrill Thompson conducted an extensive test of ARIA menus.

It is all in the semantics

As you may have guessed by now, adhering to semantic structures that HTML already offers today will get you a long long way towards accessible web content. In fact, most web content that doesn’t need special widgets will most probably be over 90% accessible by just using proper semantics and honoring a few extras that are in styling.

Only if you need to use widgets that are not provided by HTML, will you really have to dig deeper and dive into standards like WAI-ARIA. But even its first rule is: Don’t use it if you don’t have to! Just sugar-coating everything with WAI-ARIA attributes you find in Google somewhere will do more harm than good. I promise!

In conclusion

If there’s one wish I have for Christmas from the web developer community at large, it is this: Be good citizens of the web, and learn proper HTML before you even so much as touch any JavaScript framework. Those frameworks are great and offer a lot of features, no doubt. But before you use hundreds of kilobytes of JavaScript to make something clickable, you may want to try if a simple button element doesn’t do the trick just as fine!

Use semantics and save yourselves a lot of extra work, because all the standard elements come with accessibility for free.

Teach others! If you’ve mastered the skills of a good HTML and CSS citizen, teach others! Get involved, contribute your knowledge and share your wisdom! You’ll help at least two more than the obvious ones with every contribution you make!

I hope this article helps a little to clarify how easy it is to gain way over 80%, if not over 90% of accessible web content just by following standards and semantics! Please feel free to share your thoughts in the comments below, and if there is something I missed that you think should belong in this collection, feel free to also let me know, and I’ll add it!

Thank you!

This topic is also available as a video presentation held at the 2016 Global Accessibility Awareness Day’s Inclusive Design 24 event.

48 thoughts on “The web accessibility basics”

  1. Marco, there are exactly my list, with one missing one: keyboard accessibility when people DO fall back on divs and spans. Because they will use divs and spans, or they will use libraries that do, and modern dynamic websites are almost all full of modals, menus, and even simple buttons that sometimes have just enough ARIA for screen readers but none for keyboards.

    1. Thank you, will add that, and because I have an Easy ARIA Tip for that, even already have more info. I hinted at it, but will make it more explicit.

    2. I just inserted another section after the quickies, titled “OK, but what about advanced widgets?”, basically linking to some examples/explanatory blog posts.

      1. Beautiful! Thanks for adding the “advanced widgets” bit. And I don’t remember if “learn HTML before coding JS” was there before, but yes, yes, yes! I keep finding pure JS sliders, or inaccessible validators that are available in the new builtins. is our friend!

  2. The other cool standard thing with the Label tag is if you can’t put a unique ID on your form for some reason, you can put the input inside of the label, then they’re automatically associated with each other without using a for attribute.

      1. Unfortunately, nesting inputs in labels is not as well supported or gives inconsistent results across browsers and screen readers. This was also pointed out elsewhere in the comments I think. So the more explicit, the better.

  3. Should websites provide a “Skip to content” link even if they use ARIA landmarks? Your blog does, so I guess the answer is “yes”?

    1. Yes, they should. Browsers do not yet offer a standard way of navigating by landmark using the keyboard, so skip links are still very useful for keyboard-only users to jump to various parts of a page, such as the main content.

  4. I like using the placeholder-element for text input fields, because the text field is shown on usual screens anyway, and an additional Label takes away preceous place. I would actually consider *not* reading it out as a bug of screenreader software.

    1. Read the article I linked to from that section, please. It explains the actual problems the placeholder attribute poses for many users who are not screen reader users. The moment you put focus into such a field, the placeholder text disappears. Try to do that with several fields just to see how the form is laid out, and you suddenly lose all context. You no longer know which field is which. Because the placeholder text doesn’t come back.

  5. I’m curious about the justification behind the unequivocal rejection of missing alt attributes — does leaving out an alt attribute make a practical difference to the experience screen-reader users have?

    1. Yes it does. The absence of the alt attribute leads to screen readers looking for other sources that could explain what that image is. A missing alt attribute is widely considered author error and must be compensated for somehow. Has been for almost as long as web accessibility has been around, close to 20 years. An explicit alt attribute with an empty string for decorative images, on the other hand, is respected as an explicit desire for this image to be marked as such by the author, and is not considered author error.

    2. It’s not universal but common for the src attribute to be attempted as the substitute Marco mentions– those long, hash-style strings of meaningless jumbles of letters and numbers that we often see in image URLs is not only useless for the user but annoying as anything. Best way to think of “oh this gear icon next to text ‘Settings’ is just decorative” is that alt=”” will shut it up, exactly as you’d want.
      So even if you’re not actually preventing the reading out of long horrible URLs to users, if you keep it in mind I find it helps me add alt=”” in those instances.

    1. Yes, by all means, feel free to share the links even to colleagues internally or which ever channel you like! 🙂 I appreciate that!

  6. Might be worth mentioning things like tags, as they help with other forms of accessibility, such as explaining an abbreviation that might not be obvious to readers (maybe they don’t speak the language well). Accessibility isn’t just about the disabilities that people might have, but any reason that might prevent them from fully accessing your content.

  7. At least in firefox, it only disappears when I actually typed something in. As long as the text element is empty, or emptied again, the placeholder appears. And on a mobile phone, I prefer placeholders, as they do not consume as much space.

    1. And that’s the problem right there. Firefox does it this way. But does Chrome? Or Edge? Or Safari? And on mobile, does Safari on iOS, Firefox on Android, Chrome, or whatever they may be called, all do it the same? You already mentioned that Firefox does it. But the others probably don’t. The spec on the placeholder attribute isn’t crystal clear on that, so browser vendors are free – in the negative sense of the term – to interpret and invent their user experience in these matters. So you are not guaranteed that the placeholder text will come back when you empty the text field. Or that it stays visible even when you put focus in there initially, and doesn’t disappear right away. All of these are interoperability problems you cannot foresee. This is why I am advising against the use of the placeholder attribute because it introduces more trouble than it’s worth.

    1. Sorry, since CSS has mostly an effect on the visual experience, I, myself, have not dug deep. I just tell people to take care of high enough contrast ratios. 😉 So I’ll have to defer this question to somebody else who happens to read these comments.

      1. Hi Marco and everybody else,

        As far as learning CSS resources go, there are several that I’d recommend. CSS: The Missing Manual is a good starting place in the form of a book, and in regard to keeping up with what’s going on in the world of CSS, (yes, there’s actually lots of stuff happening), read the CSSTricks website.

  8. I was under the impression that the SVG tag did not accept an alt attribute and that a child title tag should be used and/or applying the a role of “img” with an aria-label attribute. Has this changed? Is there a best practice for SVG elements which serve as decoration only (e.g, )?

    I would also like to point out that your comments form does not use labels in the form (only placeholders) and that I mixed the fields up as a result. There is truth to what you say! 🙂

    1. Looks like the comment form swallowed my HTML. The example was that of an img tag used for an icon which has an empty alt attribute.

    2. No, I didn’t mean to say to use the alt attribute on SVGs, but the appropriate equivalent.

What are your thoughts?