# Limited render-blocking resources in head - **Pattern:** `ab-002525` (`site-health-check.performance-signals.minimal-blocking`) - **Severity:** info - **Lifecycle:** active - **Last modified:** 2026-04-18 - **Canonical URL:** https://auditbuffet.com/patterns/ab-002525 - **License:** CC-BY-4.0 — attribute to AuditBuffet Pattern Catalog (https://auditbuffet.com/patterns/ab-002525) ## Why it matters Synchronous scripts in `` block the HTML parser — the browser stops building the DOM and waits for each script to download, parse, and execute before continuing. On slow connections, 8+ blocking scripts can add multiple seconds to Time to First Paint. ISO 25010 performance-efficiency identifies render-blocking as a direct impairment to perceived responsiveness. The fix is attribute-level: adding `defer` or `async` costs nothing and eliminates the blocking behavior. Scripts that lack these attributes are typically there by accident — legacy integrations, copy-pasted snippets, or tools that don't set them by default. ## Severity rationale Info because the actual impact depends on script count and sizes — a single small inline script is negligible, but this rating reflects the pattern rather than guaranteed high cost. ## Remediation Add `defer` to external scripts in `` that are not critical to initial render. Use `async` for independent scripts like analytics that do not depend on other scripts: ```html ``` `type="module"` scripts are deferred by default. For Next.js, the ` ``` `defer` preserves execution order and runs after parsing. `async` runs as soon as downloaded (use for independent scripts like analytics). For modern code, `type="module"` is deferred by default. --- ## External references - iso-25010 performance-efficiency.time-behaviour Taxons: performance HTML version: https://auditbuffet.com/patterns/ab-002525