What does "Liquid error: invalid url input" mean in Shopify?

It means a line in your theme asked Shopify for an image URL and gave it nothing to work with. The image_url filter needs a real Shopify image, and when it gets an empty image setting, a collection or product with no picture, or a web address typed as text, Shopify prints Liquid error (sections/hero line 4): invalid url input on the page where the picture should be.

The quick fix is to give it the image: upload a picture to the empty setting in the theme editor, or add an image to the collection the section shows. The lasting fix is a check in the code so an empty image shows a placeholder instead of an error. Both are below, along with what Shopify printed for each of 28 image cases we ran on a development store on 23 October 2026.

How do I find which image is causing it?

Read the text in brackets. The error names the file and the line, without the .liquid ending. sections/probe line 1 means line 1 of sections/probe.liquid; templates/index line 23 means line 23 of the homepage template. Then match the line to one of these:

If you cannot tell which it is from the editor, open Online Store, Themes, the three dots, Edit code, open the named file and go to the line number. The word straight before | image_url is the thing that is empty.

What did Shopify print when we tested it?

We ran a test theme on a Shopify development store with Shopify CLI 3.93.1 on 23 October 2026, put each image case on the homepage, read the rendered HTML, and deleted the theme afterwards. Every product on that store has a photo, so the empty product case was tested with an empty value; the empty collection rows are the real world version of the same thing.

Three things in that table matter. First, the error replaces only the one image. The text, the rest of the section and the rest of the page all rendered, so on a live store it looks like one odd line of text, not a broken store. Second, collection.image and collection.featured_image are not the same thing: the first is only the image you uploaded to the collection, the second falls back to a product photo, and only an empty collection breaks both. Third, the older filter hides the problem rather than fixing it, which is why a theme can switch from img_url to image_url and suddenly show errors that were grey boxes before.

How do I fix it in the theme code?

Check the image before asking for its URL, and render something else when it is empty. This is the pattern that rendered cleanly in our test:

{%- if section.settings.image != blank -%}
  {{ section.settings.image | image_url: width: 1200 | image_tag: loading: 'lazy' }}
{%- else -%}
  {{ 'image' | placeholder_svg_tag: 'placeholder' }}
{%- endif -%}

For a collection, prefer the fallback Shopify already gives you:

{%- assign pic = collection.image | default: collection.featured_image -%}
{%- if pic != blank -%}
  {{ pic | image_url: width: 600 | image_tag }}
{%- endif -%}

A few rules that follow from the test:

• Guard the value, not the output. Wrapping the image_tag in a check does nothing once image_url has already failed. The if has to test the image itself.
• Do not swap back to img_url to silence it. Shopify lists img_url as deprecated, and the grey GIF it returns is still an empty picture, just a quieter one.
• Keep widths between 1 and 5760. Above that Shopify reduces the number without telling you; at 0 it prints a different error, Width must be between 1 and 5760, usually because a range setting was blank or a calculation came out at zero.

Can I use an image from another website with image_url?

No. In our test a full https:// address failed the same way an empty setting did, whether it was typed into the code or saved in a text setting. image_url only works on images Shopify hosts: files you uploaded, product and collection images, and image settings. To use an outside picture, upload it to Content, Files in the Shopify admin and pick it in an image setting, or have the theme write the address straight into an <img src> without the filter. The file_url filter is not a check either: given a file name that does not exist, it still returned a normal looking URL, which then 404s in the browser.

Why did this error appear after I changed or updated my theme?

Usually because the new theme expects images the old one did not. Section and block image settings start empty on a fresh install, and a well built theme shows a placeholder until you fill them. A theme that skips the check shows this error instead, once per empty image. The second common cause is a theme update that moved from img_url to image_url, which turns quiet grey boxes into visible errors. Your products and images are not lost in either case; the section is reading a setting that has not been filled in on this theme yet. If you edited the old theme's code, what happens to your edits when a theme updates explains what carries over.

Where these results come from

Every rendered value and error message above comes from one test theme with 28 image cases, run on a Shopify development store on 23 October 2026 with Shopify CLI 3.93.1 and deleted afterwards. The store had 13 products, all with photos; the 3 collections we checked had no uploaded image, and one of them, Home page, had no product photos to fall back on. The img_url deprecation is from Shopify's Liquid filter reference.

If the space is empty with no error text at all, it is a different fault, covered in why there is blank space around Shopify images. If whole sections are missing, see why a Shopify homepage is blank after installing a theme. And if the error came up while pushing a theme rather than on the storefront, what "default can't be blank" means covers the schema side.