michtio/craftcms-claude-skills/craft-twig-guidelines

Twig Coding Standards — Craft CMS 5

Coding conventions for Twig templates in Craft CMS 5 projects. These apply to all Twig code — atomic components, views, layouts, builders, partials.

Companion Skills — Always Load Together

When this skill triggers, also load:

• `craft-site` — Template architecture and component patterns. Required when creating or editing components, layouts, views, or builders.
• `craft-content-modeling` — Content architecture. Required when template code involves element queries, field access, or section decisions.

For Twig architecture patterns (atomic design, routing, builders), see the craft-site skill. For PHP coding standards, see craft-php-guidelines.

Documentation

• Twig in Craft: https://craftcms.com/docs/5.x/development/twig.html
• Template tags: https://craftcms.com/docs/5.x/reference/twig/tags.html
• Template functions: https://craftcms.com/docs/5.x/reference/twig/functions.html
• Twig 3 docs: https://twig.symfony.com/doc/3.x/

Use WebFetch on specific doc pages when something isn't covered here.

Variable Naming

Single-word, descriptive, lowercase preferred. When multi-word is needed, use camelCase.

{# Correct #}
{% set heading = entry.title %}
{% set image = entry.heroImage.one() %}
{% set items = navigation.links.all() %}
{% set element = props.get('url') ? 'a' : 'span' %}
{% set buttonText = entry.callToAction %}
{% set containerClass = 'max-w-3xl' %}
 
{# Wrong — abbreviations #}
{% set el = props.get('url') ? 'a' : 'span' %}
{% set btn = entry.callToAction %}
{% set nav = navigation.links.all() %}
 
{# Wrong — snake_case #}
{% set button_text = entry.callToAction %}
{% set container_class = 'max-w-3xl' %}

No abbreviations: element not el, button not btn, navigation not nav, description not desc.

Prefer single-word names when context makes the meaning clear (e.g. heading inside a component is better than sectionHeading). But multi-word camelCase is perfectly fine when needed for clarity.

Null Handling

?? is the default. Always safe, always portable.

??? (empty coalesce) is acceptable if the project already has nystudio107/craft-emptycoalesce or nystudio107/craft-seomatic installed — both provide the operator. But never install a plugin just for ???. Check composer.json first.

{# Always correct #}
{% set heading = entry.heading ?? '' %}
{% set image = entry.heroImage.one() ?? null %}
{{ props.get('label') ?? 'Default' }}
 
{# OK if empty-coalesce or SEOmatic is installed — checks empty, not just null #}
{% set heading = entry.heading ??? '' %}
 
{# Wrong — verbose, unnecessary #}
{% if entry.heading is defined and entry.heading is not null %}
{% if entry.heading is not defined %}

Craft 5 supports the nullsafe operator (?.). Use it for deep traversal through chains that may have null links — it propagates null cleanly without the verbose is defined and is not null dance:

{# Reach for ?. when any link in the chain may be null #}
{{ entry?.author?.fullName ?? 'Anonymous' }}
 
{# ?? alone is enough when only the leaf is in question #}
{{ entry.title ?? '' }}

?? stays the right tool for simple "value or fallback" cases; ?. is for chains where intermediate links may be missing. Don't reach for ?. on a single property access — it adds noise without adding safety.

Whitespace Control

Use {%- and {{- for whitespace trimming. Never use {%- minify -%}.

{# Correct — surgical whitespace control #}
{%- set heading = entry.title -%}
{%- if heading -%}
    {{- heading -}}
{%- endif -%}
 
{# Wrong — deprecated minification approach #}
{%- minify -%}
    {% set heading = entry.title %}
{%- endminify -%}

Apply whitespace control on tags that produce unwanted blank lines in output. Not every tag needs it — use where visible output whitespace matters.

Include Isolation

Every {% include %} MUST use only. No exceptions.

{# Correct — explicit, isolated #}
{%- include '_atoms/buttons/button--primary' with {
    text: entry.title,
    url: entry.url,
} only -%}
 
{# Wrong — ambient variables leak in #}
{%- include '_atoms/buttons/button--primary' with {
    text: entry.title,
    url: entry.url,
} -%}

Without only, a component can silently depend on variables from its parent scope, creating invisible coupling.

No Macros for Components

Never use {% macro %} for UI components. Macros don't support extends/block and their scoping model differs from includes.

{# Wrong — macro for a component #}
{% macro button(text, url) %}
    <a href="{{ url }}">{{ text }}</a>
{% endmacro %}
 
{# Correct — include with isolation #}
{%- include '_atoms/buttons/button--primary' with {
    text: text,
    url: url,
} only -%}

Macros are acceptable for utility functions that return strings (e.g., formatting helpers), not for rendering UI.

Comment Headers

Every component file gets a section header comment:

{# =========================================================================
   Component Name
   Brief description of what this component does.
   ========================================================================= #}

Props files, variant files, views, layouts — all get headers. The ========= separator matches the PHP convention from craft-php-guidelines.

Craft Twig Helpers

{% tag %} — Polymorphic Elements

Primary tool for rendering elements whose tag name depends on props.

{%- set element = props.get('url') ? 'a' : 'span' -%}
 
{%- tag element with {
    class: classes.implode(' '),
    href: props.get('url') ?? false,
    target: props.get('target') ?? false,
    rel: props.get('rel') ?? false,
    aria: {
        label: props.get('label') ?? false,
    },
} -%}
    {{ props.get('text') }}
{%- endtag -%}

Rules:

• Variable name must be descriptive: element, heading, wrapper. Never el, hd.
• false omits an attribute entirely from the rendered HTML.
• null also omits. Use false when explicitly excluding, null when absent.
• class accepts arrays with automatic falsy filtering.
• aria and data accept nested hashes that expand to aria-* / data-* attributes.

tag() — Inline Element Function

For simple elements without complex inner content:

{{ tag('span', { class: 'sr-only', text: '(opens in new window)' }) }}
{{ tag('img', { src: image.url, alt: image.title, loading: 'lazy' }) }}
{{ tag('i', { class: ['fa-solid', icon], aria: { hidden: 'true' } }) }}
 
{# Craft 5.10+: pass a string as the second arg as a text-only shortcut #}
{{ tag('span', 'Read more') }}

• text: key = HTML-encoded content.
• html: key = raw HTML content (trusted input only).
• Self-closing elements (img, input, br) handled automatically.

attr() — Attribute Strings

For building attributes in non-tag contexts:

<div{{ attr({ class: ['card', active ? 'card--active'], data: { id: entry.id } }) }}>

Returns a space-prefixed attribute string. Same false-means-omit and class array filtering as {% tag %}.

|attr Filter

For merging attributes onto existing HTML strings:

{{ svg('@webroot/icons/check.svg')|attr({ class: 'w-4 h-4', aria: { hidden: 'true' } }) }}

|parseAttr Filter

For extracting attributes from an HTML string into a hash for manipulation:

{% set attributes = '<div class="foo" data-id="1">'|parseAttr %}
{# attributes = { class: 'foo', data: { id: '1' } } #}

|append Filter

For adding content to an element string:

{{ svg('@webroot/icons/logo.svg')|append('<title>Company Logo</title>', 'replace') }}

svg() Function

{{ svg('@webroot/icons/logo.svg') }}
{{ svg(entry.svgField.one()) }}

Combine with |attr for classes and aria attributes. Use |append for accessible labels inside the SVG.

url() with false Params (Craft 5.11+)

Passing false as the second argument strips every query-string param from an absolute URL. Canonical links, share URLs, and "clear filters" links:

<link rel="canonical" href="{{ url(craft.app.request.absoluteUrl, false) }}">
<a href="{{ url(craft.app.request.absoluteUrl, false) }}">Clear filters</a>

An array still merges params in; false removes them all. The stripping only applies when the passed-in URL is absolute, so feed it a full URL, not a path. PHP has the same call as UrlHelper::url($url, false), plus UrlHelper::removeParams($url, [...]) and UrlHelper::removeAllParams($url) for finer control. Before 5.11, rebuild the clean URL with siteUrl(craft.app.request.pathInfo) instead.

heading() / h() / h1()…h6() — Programmatic Headings (Craft 5.10+)

Build heading tags from a dynamic level without string-concatenation. Useful in components that receive a level prop and need to render the matching tag without doing tag('h' ~ level, text) manually.

{# heading(level, text-or-attributes) — level is an int 1-6 #}
{{ heading(2, 'Section title') }}                     {# <h2>Section title</h2> #}
{{ heading(3, { class: 'text-xl', text: 'Subsection' }) }}
 
{# h() is the short alias for heading() #}
{{ h(2, 'Section title') }}
 
{# Bound-level shortcuts — only attributes/text needed #}
{{ h1('Page title') }}
{{ h2('Section') }}
{{ h6({ class: 'sr-only', text: 'Hidden heading' }) }}

These are stateless tag builders — there's no auto-incrementing or current-level tracking. Components that need to thread a level across nested contexts still pass it as a prop. heading() throws InvalidArgumentException when level is outside 1-6.

Filter Additions (Craft 5.10+)

{{ price|number(locale: 'de-DE') }}                   {# locale arg #}
{{ entry.postDate|datetime('long', withTimeZone: true) }}
{{ deadline|time('short', withTimeZone: true) }}
{{ maybeNull|timestamp }}                              {# returns "now" for null/empty #}

Filtering and Mapping — Default to collect()

For data manipulation in templates, default to `collect()` — one consistent, chainable API (where, firstWhere, groupBy, keyBy, unique, pluck, map, filter, sortByDesc) instead of mixing idioms:

{% set newsByYear = entries.collect
    .where('type', 'news')
    .sortByDesc('postDate')
    .groupBy(e => e.postDate|date('Y')) %}

The bare Twig/Craft array filters are fine for a single trivial operation inline — {% for e in entries|filter(e => e.enabled) %} — where a Collection adds nothing. But Twig's |filter/|map return plain arrays and Craft's |where/|firstWhere/|group/|index go through ArrayHelper, so they don't chain like Collection methods; once you need more than one step, switch to collect(). Don't mix both styles arbitrarily.

There is no `|indexBy` filter — key a list with |index (or .keyBy() on a Collection) and bucket with |group (or .groupBy()). (|where, |firstWhere, |contains, |group, |index, |explodeClass/|explodeStyle are all Craft-registered filters.)

Safe Output and Inline Assets