About this tool
Audit image response exports before deployment so client-hints-based variants (DPR, Width, Viewport-Width) include explicit Vary and Accept-CH coverage without unstable cache-key sprawl.
The Image Client Hints Vary Checker verifies that servers using DPR, Width, or Viewport-Width client hints to transform images also include the corresponding Sec-CH tokens in their Vary response headers. Without these tokens, CDN and proxy caches can conflate variants intended for different device classes, delivering a 1x image to a 3x display or a desktop-sized asset to a mobile viewport. The tool maps every hint-to-Vary pairing across all image responses on a page.
- Parses rows in URL|image-url|vary|accept-ch|requested-hints|status|context|bytes format and normalizes relative image URLs with an optional base URL.
- Flags missing Vary headers, hint-specific Vary gaps (Sec-CH-DPR/Width/Viewport-Width), and requested hints not declared in Accept-CH.
- Highlights wildcard and high-cardinality Vary usage, then prioritizes pages where critical image risk bytes exceed your configured budget.
How to use Client Hints Vary Checker
Enter a URL and the checker fetches the page, identifies which client hints are advertised via Accept-CH, and then inspects every image response to confirm the Vary header includes matching Sec-CH-DPR, Sec-CH-Width, or Sec-CH-Viewport-Width tokens. Mismatches are flagged with the specific missing token and the image's byte weight so you can triage cache-correctness fixes by performance impact. Re-audit after configuration changes to validate coverage.
When this tool is useful
- Audit responsive image delivery before launch when DPR, Width, or Viewport-Width client hints are enabled at CDN or edge layers.
- Catch missing hint-specific Vary coverage that can cause mismatched variants from shared caches.
- Prioritize critical templates where client-hints cache risk can degrade LCP consistency across devices.
Practical tips
- Treat requested hints and cache keys as a pair: if DPR/Width/Viewport-Width are used to transform images, include matching Sec-CH-* tokens in Vary.
- Keep Accept-CH declarations explicit and minimal so hints are intentional, auditable, and stable across deployments.
- Avoid wildcard and high-cardinality Vary usage unless you have measured evidence it is required.
Why people use this tool
Client hints let servers tailor image resolution and dimensions to each device, but the cache layer must know which hints influenced the response. If Vary omits the relevant Sec-CH token, a high-DPR variant cached for one request may be served to a low-DPR device, wasting bandwidth, or a small variant may reach a high-density screen, degrading visual quality. Correct Vary alignment is the mechanism that makes client-hint-driven image optimization cache-safe.
Related search intents
image client hints checker, vary sec-ch checker, image dpr width vary audit, client hints image cache checker.