What is responsive image HTML?
Responsive image HTML lets the browser choose the best image file for each device. You list several sizes in srcset, describe the layout width in sizes, and the browser downloads only what it needs. This tool resizes your image, encodes AVIF, WebP and JPEG variants, and writes the markup for you.
srcset vs sizes vs <picture>
| Feature | What it does | Use it for |
|---|---|---|
srcset | Lists files with width descriptors such as 640w | Resolution switching |
sizes | Tells the browser the rendered width | Accurate file selection |
<picture> | Groups <source> elements by format or media query | AVIF/WebP with fallback, art direction |
How to create responsive images in four steps
- Add one high-resolution image. Start from the largest version you have.
- Enter your breakpoints. The tool never upscales, so widths above the original are capped.
- Describe the display width in the sizes field, or pick a preset.
- Generate the files, copy the markup and upload the ZIP contents to your server.
Why width and height attributes matter
Add width and height to every image. The browser computes the aspect ratio, reserves the space and avoids Cumulative Layout Shift. Then set max-width:100%; height:auto in CSS so the image still scales fluidly.
Lazy loading rules that protect your LCP
Add loading="lazy" to images below the fold, and never to your hero image. For the Largest Contentful Paint element, choose Eager in this tool. It adds fetchpriority="high", which tells the browser to fetch that file first. Read more in the Fetch Priority guide and the LCP guide.
Best practices for responsive images
- Compress each variant. Run extra passes through the Image Compressor when you need smaller files.
- Resize with precision using the Image Resizer when you need exact dimensions or crops.
- Convert legacy files with the All-in-One Image Converter.
- Add a blur placeholder with the BlurHash & LQIP Generator to make loading feel instant.
- Choose PNG as the fallback only when you need transparency. JPEG stays smaller for photos.
- Use meaningful file names such as
red-running-shoes-640.webp.
Image SEO and Google's people-first guidance
Google indexes images that appear in standard <img> or <picture> markup, as its image SEO documentation explains. Write alt text that describes the image for real readers, and place the image near relevant text. Follow the principles of helpful, people-first content instead of stuffing keywords. For the full attribute reference, see MDN's responsive images guide.
Frequently asked questions
What is a responsive image?
A responsive image is an image that the browser picks from several file sizes based on the screen width and pixel density. Phones download a small file, and large monitors download a big one.
What is the difference between srcset and sizes?
The srcset attribute lists the available files and their real widths, for example 640w. The sizes attribute tells the browser how wide the image will display in your layout, so it can choose the best file from srcset.
When should I use the <picture> element?
Use <picture> when you want to offer modern formats such as AVIF and WebP with a JPEG fallback, or when you need art direction, meaning a different crop at different breakpoints.
Should I always add width and height attributes?
Yes. These attributes let the browser reserve space before the image loads, which prevents layout shift. Pair them with CSS such as max-width:100% and height:auto.
Should I lazy-load every image?
No. Lazy-load images below the fold. Load your hero or LCP image eagerly, and add fetchpriority="high" so the browser fetches it early.
Does this tool upload my image?
No. The tool resizes and encodes every variant inside your browser, so your image never leaves your device.