# Bad value X for attribute “srcset” on element “source”: Starts with empty image-candidate string.

> Canonical HTML version: https://rocketvalidator.com/html-validation/bad-value-x-for-attribute-srcset-on-element-source-starts-with-empty-image-candidate-string
> Attribution: Rocket Validator (https://rocketvalidator.com)
> License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/)

A `srcset` value that begins with a comma has an empty first image candidate, which usually means the URL that should come before that comma was never filled in.

`srcset` holds a comma-separated list of image candidate strings. Each one is a URL, optionally followed by a width descriptor such as `800w` or a pixel density descriptor such as `2x`. When the value starts with a comma, or with spaces and then a comma, nothing comes before the first separator, and the validator reports an empty candidate at the start of the list.

The usual source is a template that writes `srcset="{{ image }}, {{ image_2x }} 2x"` and prints the attribute even when the image fields are empty. With only the first field missing, the value becomes `, hero-2x.webp 2x`. With both missing, it becomes `,  2x`. Browsers skip the leading comma, so in that second case they read `2x` as the image URL. Inside `<picture>`, the browser picks that `<source>` and requests a file called `2x` instead of using the `<img>` fallback, and the image fails to load.

Fill in the missing URL, or leave the `<source>` out when there is no image for it. The `<img>` inside `<picture>` still provides the fallback.

## Invalid example

```html
<picture>
  <source srcset=", hero-2x.webp 2x" type="image/webp">
  <img src="hero.jpg" alt="A mountain lake at sunrise">
</picture>
```

## Valid example

```html
<picture>
  <source srcset="hero.webp, hero-2x.webp 2x" type="image/webp">
  <img src="hero.jpg" alt="A mountain lake at sunrise">
</picture>
```

When no WebP version exists, drop the `<source>`:

```html
<picture>
  <img src="hero.jpg" alt="A mountain lake at sunrise">
</picture>
```