You can run the following checks as part of Theme Check. Each check identifies a specific error or a place in your code where a best practice is not being followed. To learn more about the check and its options, click on the name of the check. ## Liquid file checks These checks analyze the style and validity of Liquid code. Some of these checks support auto-correction using the `--auto-correct` flag.
Check Severity Purpose Auto-correction
AppBlockValidTags Error Identifies forbidden Liquid tags in theme app extension app block and app embed block code.
AssetPreload Warning Encourages preloading of assets using Liquid filters, rather than HTML attributes.
AssetSizeAppBlockCSS Error Prevents theme app extensions from using CSS files larger than the configured threshold.
AssetSizeAppBlockJavascript Error Prevents theme app extensions from using JavaScript files and external scripts with a compressed size larger than the configured threshold.
AssetSizeCSS Error Prevents themes from using CSS files larger than the configured threshold.
AssetSizeJavaScript Error Prevents using theme JavaScript files and external scripts with a compressed size greater than the configured threshold.
BlockIdUsage Warning Warns against the use of block IDs in conditional statements and case statements.
CdnPreconnect Warning This check is aimed at signaling the redundant preconnect to Shopify's CDN.
ContentForHeaderModification Error Identifies code that tries to parse content_for_header .
DeprecateBgsizes Warning Discourages use of the bgset extension instead of the image-set attribute for loading background images.
DeprecateLazysizes Warning Discourages use of the lazysizes library for lazy loading images, iframes, and scripts.
DeprecatedFilter Warning Discourages using deprecated filters in themes. Yes
DeprecatedTag Error Discourages using deprecated tags in themes.
EmptyBlockContent Warning Detects instances where the Liquid tag {% content_for 'blocks' %} is used when the associated schema blocks array is empty or undefined.
ImgWidthAndHeight Error Enforces setting the width and height attributes on img tags.
LiquidFreeSettings Warning Identifies when a theme is using the {% liquid %} tag within Settings values.
LiquidHTMLSyntaxError Error Identifies Liquid and HTML syntax errors.
MissingAsset Error Makes sure that all asset files referenced by the asset_url filter exist.
AppBlockMissingSchema Error Ensures schema is present in app blocks in theme app extensions.
MissingTemplate Warning Identifies when a resource is referenced using a render , section , or include tag, but doesn't exist. Yes
PaginationSize Warning Ensures that objects are paginated with performant sizes so too many objects are not loaded at once.
ParserBlockingJavaScript Error Identifies script tags that don't have defer or async attributes, avoiding parser-blocking JavaScript.
RemoteAsset Warning Discourages use of third party domains for hosting assets.
RequiredLayoutThemeObject Error Makes sure that the theme.liquid layout file contains the required {{ content_for_header }} and {{ content_for_layout }} objects. Yes
SchemaPresetsBlockOrder Warning Makes sure that the section and block schema presets are correctly used in the block_order.
SchemaPresetsStaticBlocks Error Warns if a preset static block doesn't have a {% content_for "block" ... %} tag in the Liquid code.
TranslationKeyExists Error Identifies references to translations that don't exist.
UnclosedHTMLElement Error Identifies instances of unclosed HTML elements in branching code.
UndefinedObject Error Identifies references to undefined Liquid objects.
UniqueStaticBlockId Error Identifies when two static blocks are using the same ID.
UnknownFilter Error Identifies references to unknown Liquid filters.
UnusedAssign Warning Identifies variable definitions that aren't used.
ValidBlockTarget Error Identifies when a block is using an invalid target.
ValidContentForArguments Error Identifies invalid arguments passed to the {% content_for %} tag
ValidLocalBlocks Error Identifies when a local block is used incorrectly.
ValidSchema Warning Identifies invalid JSON in {% schema %} tags.
ValidSchemaName Error Identifies invalid values for the schema name property.
ValidStaticBlockType Error Identifies when a static block is using an invalid type.
VariableName Warning Identifies variable names that don't adhere to a selected naming convention.
## JSON file checks These checks analyze the syntax, content and structure of JSON files.
Check Severity Purpose Auto-correction
JSONMissingBlock Error Identifies when a JSON template file is referencing block types that don't exist.
JSONSyntaxError Error Identifies invalid JSON files in themes.
MatchingTranslations Warning Identifies missing or additional translations in locale files. Yes
ValidHTMLTranslation Warning Identifies invalid HTML inside translations.