About this tool
Review image markup exports before launch so missing dimension attributes, ratio mismatches, and oversized render targets do not increase layout shift risk or reduce perceived performance.
The Image Dimension Attribute Checker scans page markup for img elements that are missing explicit width and height attributes or whose declared dimensions conflict with the image's natural resolution. It detects upscaling, ratio mismatches, and absent dimension pairs that prevent the browser from reserving accurate layout space. Each finding includes the element's source, declared values, and computed natural size for fast triage.
- Parses rows in URL|image|width|height|natural-dimensions|context|loading format and normalizes URLs with an optional base URL.
- Flags missing or invalid width/height attributes, invalid natural dimensions, and critical images marked loading=lazy.
- Detects declared-vs-natural aspect-ratio drift and source-upscale risk with configurable tolerance thresholds.
How to use Image Dimension Checker
Paste a URL and the tool retrieves the page, measures every img element's natural dimensions, and compares them to the width and height attributes in the HTML. Rows are sorted by layout-shift risk so CLS-sensitive images surface first. After fixing missing or mismatched attributes in your templates, re-run the audit to verify that every image now reserves the correct space before it loads.
When this tool is useful
- Audit image markup before launching template changes that touch hero, card, or article image components.
- Catch missing width/height attributes and ratio mismatches that can increase layout instability.
- Prioritize rows where declared dimensions upscale small sources or conflict with expected natural dimensions.
Practical tips
- Always emit width and height attributes from your CMS or component system to reserve layout space before images load.
- Keep declared and natural aspect ratios aligned so responsive crops do not create unexpected stretching or shift behavior.
- Treat critical hero and LCP images with extra care: avoid loading=lazy and verify dimensions after design updates.
Examples you can test
These examples show the kind of real input and reviewed output this tool is designed to support. Use them as a starting point before pasting your own production content, then compare the output with the destination system that will use the result. The goal is not only to produce a value, but to make the input assumptions, output format, and review step clear enough that the result can be trusted in a real workflow.
Find an image missing width and height
Example input
URL: /blog | Image: /images/chart.png | width: missing | height: missing | natural: 1200x675
Expected output
CLS risk: the browser cannot reserve the correct 16:9 space before the image loads.
Adding matching width and height attributes lets the browser calculate aspect ratio before the image bytes arrive.
Catch a declared ratio mismatch
Example input
Image: /hero.jpg | width: 800 | height: 800 | natural dimensions: 1600x900
Expected output
Mismatch: declared dimensions reserve a square box for a 16:9 source and may cause layout or crop drift.
Wrong dimensions can be as harmful as missing dimensions because the reserved space still changes once CSS and image rendering settle.
Validation checklist
Run through these checks before copying the result into a CMS, codebase, spreadsheet, campaign, support ticket, or production document. Small formatting differences, unit assumptions, hidden whitespace, and platform-specific rules are common sources of mistakes in quick browser tools, so the final review should happen in the same context where the output will be used.
- Confirm every content, card, and hero image has both width and height attributes when markup is server-rendered.
- Compare declared width/height ratio with natural image ratio before shipping template or CMS changes.
- Watch for source-upscale rows where declared dimensions are larger than the actual image file.
- Retest critical LCP images after design changes because hero crops and dimensions often drift across breakpoints.
Why people use this tool
Missing width and height attributes are one of the most common causes of Cumulative Layout Shift because the browser cannot reserve space for an image until it knows its intrinsic ratio. When dimensions are present but wrong, the reserved space still collapses or expands on load, producing visible content jumps that hurt both user experience and Core Web Vitals scores. Accurate dimension attributes are a low-effort, high-impact fix for layout stability.
Related search intents
image dimension attribute checker, img width height checker, image ratio mismatch audit, cls image attribute checker.