Image Delivery Audit Kit

Audit one browser-local image and submitted delivery metadata for responsive coverage, decoded memory, bandwidth assumptions, and render risks without changing the image.

Web developers reviewing an existing image and its intended HTML delivery before manually changing site assets or markup.

Delivery metadata (strict JSON)Choose one existing image

The file is size-preflighted before local reading. No conversion, upload, fetch, publish, or cache change is available.

Audit result

Hosted sample: metadata-only plan

{
  "ok": true,
  "schema_version": "utilito.product-kit.v1",
  "kit": {
    "id": "image-delivery-audit-kit",
    "version": "2.0.0"
  },
  "result": {
    "status": "metadata_only_audit_plan",
    "actual_file_facts_available": false,
    "file_bytes_received": false,
    "signature": null,
    "actual_mime": null,
    "decoded_dimensions": null,
    "decode_succeeded": null,
    "submitted_delivery": {
      "src": "/images/hero.webp",
      "srcset": [
        {
          "src": "/images/hero-640.webp",
          "width": 640,
          "bytes": 64000
        },
        {
          "src": "/images/hero-1280.webp",
          "width": 1280,
          "bytes": 160000
        }
      ],
      "sizes": "(max-width: 640px) 100vw, 1200px",
      "width": 1200,
      "height": 630,
      "loading": "lazy",
      "decoding": "async",
      "submitted_by_caller": true,
      "independently_verified": false
    },
    "declared_facts": {
      "format": "image/webp",
      "alpha": "unknown",
      "animation": "unknown",
      "submitted_by_caller": true,
      "independently_verified": false
    },
    "assumptions": {
      "requests": 10000,
      "cache_hit_ratio": 0.8,
      "effective_bandwidth_bps": 10000000,
      "render_count": 2,
      "submitted_by_caller": true,
      "independently_verified": false
    },
    "responsive_coverage": [
      {
        "viewport_width": 375,
        "dpr": 1,
        "slot_width": 375,
        "required_width": 375,
        "selected_width": 640,
        "selected_bytes": 64000,
        "upscaling": false,
        "submitted_metadata": true
      },
      {
        "viewport_width": 768,
        "dpr": 2,
        "slot_width": 1200,
        "required_width": 2400,
        "selected_width": 1280,
        "selected_bytes": 160000,
        "upscaling": true,
        "submitted_metadata": true
      },
      {
        "viewport_width": 1440,
        "dpr": 2,
        "slot_width": 1200,
        "required_width": 2400,
        "selected_width": 1280,
        "selected_bytes": 160000,
        "upscaling": true,
        "submitted_metadata": true
      }
    ],
    "intrinsic_aspect": {
      "submitted_width": 1200,
      "submitted_height": 630,
      "actual_width": null,
      "actual_height": null
    },
    "estimates": {
      "decoded_memory": {
        "bytes": 3024000,
        "formula": "submitted_intrinsic_width * submitted_intrinsic_height * 4",
        "assumptions": [
          "hosted dimensions are caller-submitted",
          "four RGBA bytes per decoded pixel"
        ]
      },
      "bandwidth": {
        "bytes": 319999999.99999994,
        "formula": "selected_candidate_bytes * requests * (1 - cache_hit_ratio)",
        "assumptions": [
          "candidate bytes, requests, and cache hit ratio are caller-submitted",
          "retries and protocol overhead excluded"
        ]
      },
      "render_demand": {
        "byte_instances": 6048000,
        "formula": "submitted_intrinsic_width * submitted_intrinsic_height * 4 * render_count",
        "assumptions": [
          "hosted dimensions are caller-submitted",
          "render count is caller-submitted",
          "estimate is arithmetic, not a measured browser benchmark"
        ]
      }
    },
    "findings": [
      {
        "code": "RESPONSIVE_GAP",
        "severity": "warning",
        "message": "At least one submitted viewport requirement has no candidate at or above its required pixel width.",
        "automatic": false
      },
      {
        "code": "UPSCALING_REQUIRED",
        "severity": "warning",
        "message": "At least one submitted viewport requirement would upscale the largest candidate.",
        "automatic": false
      },
      {
        "code": "ALPHA_AMBIGUOUS",
        "severity": "review",
        "message": "Caller did not declare whether the image uses alpha.",
        "automatic": false
      },
      {
        "code": "ANIMATION_AMBIGUOUS",
        "severity": "review",
        "message": "Caller did not declare whether the image is animated.",
        "automatic": false
      }
    ],
    "fix_checklist": [
      "Review RESPONSIVE_GAP.",
      "Review UPSCALING_REQUIRED.",
      "Review ALPHA_AMBIGUOUS.",
      "Review ANIMATION_AMBIGUOUS."
    ],
    "claims": {
      "lighthouse_score": false,
      "core_web_vitals_measurement": false,
      "browser_benchmark": false,
      "performance_guarantee": false
    },
    "limitations": [
      "Hosted output uses metadata only and cannot establish actual file signature, MIME, decode success, dimensions, pixels, alpha, or animation.",
      "Browser-local facts apply only to the exact selected bytes and one browser-native decode.",
      "All cache, bandwidth, request, viewport, and render-count values are caller assumptions.",
      "This is not Lighthouse, Core Web Vitals measurement, a browser benchmark, or a performance guarantee."
    ]
  },
  "receipt": {
    "input_bytes": 673,
    "output_bytes": 4055,
    "operations": 5,
    "omitted_items": 0,
    "warnings": []
  },
  "provenance": {
    "deterministic": true,
    "model_used": false,
    "network_used": false,
    "storage_used": false,
    "file_bytes_received": false,
    "core_versions": {
      "image_delivery_audit_kit": "2.0.0",
      "image_delivery_audit": "utilito.image-delivery.v1",
      "size_bandwidth": "existing-core",
      "rendering_limits": "existing-core",
      "rendering_cache": "existing-core"
    }
  },
  "error": null
}

What this audit can establish

Hosted output uses submitted metadata only. Actual signature, MIME, decode success, dimensions, and pixel facts appear only after the selected local bytes pass exact signature checks and a browser-native decode.

Decoded-memory, bandwidth, and render-demand values show their formulas and caller assumptions. They are not Lighthouse scores, Core Web Vitals measurements, browser benchmarks, or performance guarantees.

Hosted output is metadata-only and cannot establish actual file signature, MIME, decode success, dimensions, pixels, alpha, or animation.
Browser-local actual facts come only from the exact selected bytes, signature sniffing, and one browser-native decoder result under hard limits and an active deadline.
Decoded memory, bandwidth, and render demand are deterministic finite arithmetic over actual dimensions where available and clearly labeled caller assumptions; they are not measurements.
The kit does not fetch, upload, convert, optimize, host, publish, deploy, purge caches, mutate assets, run Lighthouse, measure Core Web Vitals, benchmark browsers, or guarantee performance.
Downloads use generation-owned Blob URLs and are published atomically, then revoked on replacement, reset, failure, stale work, and pagehide.