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Use when reviewing image assets, markup, and CDN or build transforms related to Use progressive JPEG encoding. Check encoded size, rendered size, loading strategy, and above-the-fold impact together.
Use when reviewing templates, rendered HTML, or shared components related to Implement accessible breadcrumb navigation. Validate the final browser-facing markup, not just the source framework abstraction.
Use when auditing metadata, crawlability, structured data, or indexability related to Implement valid BreadcrumbList schema. Verify the rendered HTML and HTTP response rather than relying only on source files.
Use when reviewing templates, rendered HTML, or shared components related to Declare UTF-8 character encoding. Validate the final browser-facing markup, not just the source framework abstraction.
Use when reviewing templates, rendered HTML, or shared components related to Set text direction for RTL languages. Validate the final browser-facing markup, not just the source framework abstraction.
Use when auditing a site's meta tag uniqueness, generating page-specific meta descriptions, or reviewing CMS templates that inject the same description globally.
Use when you need to find the 2-3 most popular and well-maintained npm packages relevant to a frontend checklist rule, validate they meet quality thresholds, and add them to the rule's frontmatter.
| name | progressive-jpeg |
| description | Use when reviewing image assets, markup, and CDN or build transforms related to Use progressive JPEG encoding. Check encoded size, rendered size, loading strategy, and above-the-fold impact together. |
| metadata | {"category":"images","priority":"low","difficulty":"beginner","estimatedTime":"10","source":"frontendchecklist.io","url":"https://frontendchecklist.io/en/rules/images/progressive-jpeg"} |
Progressive JPEGs display a low-quality preview immediately rather than loading line-by-line—users see something faster, improving perceived performance even if total load time is similar.
Check if JPEG images are saved in progressive format for better perceived performance.
Convert baseline JPEGs to progressive format for improved loading experience.
Explain how progressive JPEGs show a low-quality preview that improves perceived performance.
Review image assets, markup, and delivery configuration related to Use progressive JPEG encoding. Flag exact files or components where format choice, sizing, or loading behavior violates the rule, and describe how to confirm the fix in DevTools.
For full implementation details, code examples, and framework-specific guidance,
see references/rule.md.
Rule page: https://frontendchecklist.io/en/rules/images/progressive-jpeg
