Frontend Style Guide by Kaliop

HTML and Templating


HTML’s syntax can be very flexible, and browsers will try to deal with errors silently. To make our code more robust and consistent, follow these rules:

  1. Valid HTML code (
  2. Lowercase tag names and attributes
  3. Always quote attribute values, with double quotes
  4. Attribute order: class first, id second, then everything else.
<p class="Form-field">
  <label class="Form-label" for="f-color">
    What is your favourite colour?
  <input class="Form-textbox" id="f-color" name="color" required>
  <a class="modalLink" href="/help/276b6de1">
    <img src="question-mark.svg" alt="Help">


Write as few HTML comments (<!-- Comment -->) as possible:

  • They should not contain technical information
  • Or references to client requirements

It’s often better to use the templating language’s comment syntax instead. This helps sending fewer bytes to users, too.


<!-- External SVG sprite support for IE -->


{# External SVG sprite support for IE #}


  • Use 2 spaces
  • Indent the contents elements (unless it’s short)

For templating languages, indent the template’s source code, not the generated HTML:

  • Indent inside control blocks (e.g. {% if %} tags)
  • In each template file, start with no indentation
<div class="page-row">
  <div class="container">
    {% block content %}{% endblock %}
{% extends 'parent.twig' %}

{% block content %}
  <h1>{{ title }}</h1>
  {% if main_text %}
    <div class="text">
      {{ main_text }}
  {% endif %}
{% endblock %}

Document structure

The basic structure of a HTML page should have:

  • The HTML5 doctype: <!DOCTYPE html>
  • A single root element: <html>
  • With two child elements: <head> and <body>

Declaring languages

Always provide a lang attribute on the root element; make sure it shows the correct language for each page, especially on multilingual sites! For more information, see this W3C tutorial.

Essential metadata

  • Add a <meta charset="UTF-8"> encoding declaration, in case it’s not already declared in the HTTP Content-Type header.
  • Always have a <title> element, with a specific content for each page.
<!DOCTYPE html>
<html lang="en">
  <meta charset="UTF-8">
  <title>Page title</title>
  <!-- Visible content -->

Adding styles

Request an external stylesheet

To add styles to a page, we generally write one (or sometimes a few) stylesheet(s) and link to it from the HTML.

Use <link rel="stylesheet" href="/url/to/styles.css"> in the page’s <head> to request an external stylesheet.


  • We want to load only one stylesheet (or 2–3 max).
  • For each stylesheet, the browser will make a HTTP request, and block rendering the page until all the CSS arrives!

Inline stylesheets

More rarely, we can write some of the styles directly in the HTML page, using <style>/* My styles */</style>

This can be useful for:

  • Some web performance techniques (“critical CSS”).
  • Styles generated depending on user preferences.

Viewport meta tag

For responsive sites, make sure you have this tag in your <head>:

<meta name="viewport" content="width=device-width">

Some sites add more parameters to the content value:

  • initial-scale=1: this should not be necessary anymore.
  • maximum-scale=1: this breaks accessibility! Avoid it.
  <meta name="viewport" content="width=device-width">
  <link rel="stylesheet" href="/dist/main.css">

Adding scripts

Like CSS, JS code can live in separate files or in the HTML document. For most uses, we recommend using an external JS file.

Request an external script

Use <script src="/url/to/script.js"></script> after the page’s content. Generally, that means putting this script tag just before the end of the body (</body> tag).

Inline scripts

The syntax for inline scripts is similar:
<script>/* JS code */</script>

This can be useful for some critical — and short! — JS code that we want to execute as soon as possible, without making a HTTP request.

Performance guidelines

  1. Load as few scripts as possible; concatenate code to make 1 (or 2–3 max) HTTP requests.
  2. Script tags block rendering. Add the async attribute or call them just before </body>.
  3. Third party scripts are often huge; load on pages that need them only.
  {# In HEAD: only short scripts that declare variables! #}
    window.modules = {};
    window._gaq = [];
  {# Short inline scripts (executed earlier) #}
  {# Call the main scripts after the page’s content #}
  <script src="/dist/vendor.js"></script>
  <script src="/dist/main.js"></script>
  {# Scripts that don’t depend on vendor/libs can use the async attribute #}
  <script async src="/dist/something.js"></script>

Semantic HTML

  • Use the appropriate HTML element to mark up content, not only <div> and <span>.
  • You can use a reference such as for details on available elements and attributes.

Links vs buttons

The rule is simple:

  • If it goes somewhere else, it’s a <a href="url"></a> element.
  • If it performs a custom JS action, it’s a <button></button> element.

Avoid <div onclick=""></div> or <li onclick=""></li>: it can’t be focused with the keyboard, can’t be read by a screen reader, doesn’t work for SEO, etc.

Always use real links (<a href="url">…</a>) to navigate between pages, including for navigating between views in “single-page” applications. It’s better for accessibility, SEO, bookmarking and sharing.

Semantic groups

In the <body> we try to group the page’s visible elements in 4 groups:

    {# logo, search, etc. #}
    {# primary navigation #}
    {# page’s main content #}
    {# more info about the site, links, etc. #}

It’s also possible to put the <nav> inside the <header>.

Use the “search” role for the main search

If the page offers a search form, use the ARIA search role on this form:

<form role="search" action="/site-search">

Important: role="search" must only appear once in the page.

Accessible HTML

We strive to create accessible user interfaces, whether the HTML is generated server-side or client-side in JavaScript. Here are a few guidelines to get you started on this topic.

Use titles for structure

  • Use H1, H2, H3 elements (lower levels are often unnecessary)
  • If this conflicts with SEO needs, see if you can find a compromise (keep the main titles, maybe change a useful H1/H2 to a H3 so that it does not clash with SEO needs but is still listed in screen readers)
  <h1>Page title</h1>
  <h2>A sub-section</h2>
  <h2>Another section</h2>

Use text labels

Outside of content managed in a CMS, we need accessible text for:

  • Logos (use the brand’s name, not "logo") and other significant images
  • Buttons or links with icons and no visible text

For links and buttons, this can look like:

<a href="">
  <img src="" alt="Subscribe Now">

  <svg class="icon">
    <title>Subscribe Now</title>
    <path d=""></path>

If you can’t add alt text to the image or icon itself, you can use aria-label on the link or button:

<a href="" aria-label="Subscribe Now">
  <i data-icon="letter"></i>

Finally, if the text is already present in context, it’s often better to have empty alt text:

<a href="">
  <img src="" alt="">
  Subscribe Now

  <svg class="icon" aria-hidden="true"><path d=""></path></svg>
  Subscribe Now

Make sure that form elements have labels

Link a form element and the relevant label using <label for="some-id"> and the id attribute.

  <label for="user-name">My Name</label>
  <input type="text" id="user-name">

  <input type="checkbox" id="user-subscribe">
  <label for="user-subscribe">Subscribe me to the newsletter</label>

If done properly, clicking the label should focus the text input (or <select> or any other form control). Note that each id attribute must be unique in the page.

Learn more

Beyond this section, see this accessibility cheatsheet for an introduction to accessibility.

JavaScript hooks

When working with a separate HTML and JS codebase (vs working on JS-centric apps with React or Vue.js), we often need to query elements from the DOM to work on.

If you’re working with BEM components (see CSS – Components), target the component classes. For instance, with jQuery:

$('.MyComponent').each(function(i, el) {
  var container = $(el);
  var items = container.find('.MyComponent-item');

Or use data attributes on elements. In the next example, the MyModal class is reponsible for styling, and the data-modal attribute is responsible for linking the button to show the modal.

<button data-modal="#forminfo-12">More info</button>
<div class="MyModal" id="forminfo-12" hidden>
  {# Inline modal’s content #}

It’s also possible to write a small HTML API for your custom JS code, with options written as data attributes:

<div class="MyModal"

UI states

Using script, we often need to change the “state” of an element in the UI. Instead of adding or removing classes, consider using:

  • Native HTML attributes such as disabled or hidden.
  • ARIA attributes such as aria-expanded="true|false".
  • Or, finally, a data attribute: data-state="my-custom-state".

Try to use id attribute values to link elements logically. Both HTML (example: <label for="some-id">) and ARIA (example: aria-labelledby="other-id") use this technique already. But make sure that the id values you use are unique in the page!

Encoding & characters

  • Always use UTF-8
  • In text content, use typographically correct characters, for example (apostrophe) or (ellipsis)
  • Avoid character references (Fançais, not Fran&#231;ais), except for invisible characters (&nbsp;)

Useful tools:

Deprecated syntaxes

The following HTML syntaxes, elements or metadata are useless or have been deprecated. You should remove them from your HTML. Eliminate distractions like a HTML Jedi.

Old doctypes, XHTML namespace

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
<html xmlns="" lang="fr" xml:lang="fr">

Use this instead:

<!DOCTYPE html>
<html lang="fr">

Default type for styles

It’s not essential, but you can remove the type attributes on stylesheet when it uses the default text/css value. So, always.

<link rel="stylesheet" type="text/css" href="url">
<style type="text/css">/* code */</style>

<!-- Better -->
<link rel="stylesheet" href="url">
<style>/* code */</style>

Default type for scripts

Same for scripts and text/javascript. And if you find a non-standard language attribute, remove it too.

<script type="text/javascript" src="url"></script>
<script type="text/javascript" language="Javascript"></script>

<!-- Better -->
<script src="url"></script>

IE Conditional Comments

Conditional comments were dropped in IE 10. They can be used if you really need to target IE 8–9, but for most projects they’re probably just useless code from an old boilerplate. For instance, you could see this:

<!--[if IE 8]><html class="ie8" lang="fr"><![endif]-->
<!--[if IE 9]><html class="ie9" lang="fr"><![endif]-->
<!--[if gt IE 9]><!--><html lang="fr"><!--<![endif]-->

Same code, cleaned up:

<html lang="fr">

X-UA-Compatible meta tag

Another deprecated IE feature:

<meta http-equiv="X-UA-Compatible" content="IE=Edge">

You will find this in a lot of projects. Why? On local network sites, IE 8–10 would automatically use a “backwards compatible” mode to render the page, trying to mimick IE 7. This tag would tell IE to avoid that, and use its best capabilities. Thankfully, IE 11 and Edge stopped this nonsense.

Totally useless meta tags

<!-- Not used in any search engine since 1997! -->
<meta name="keywords" content="make money, free cash, easy">

<!-- NEVER worked, still exists on many websites! -->
<META NAME="MSSmartTagsPreventParsing" CONTENT="TRUE">