Admin UI extension builds successfully, but shopify app dev preview fails to start

Shopify App Store
1

Hi all — I’m running into a persistent shopify app dev preview failure for an Admin UI extension, and I’m hoping someone from Shopify can help trace it.

Summary

My app and extension build successfully locally, but the dev preview fails to start afterward.

The failure happens at the preview step on the dev store, specifically when Shopify hits:

https://image-search-dev.myshopify.com/app_dev/unstable/graphql.json

and then returns:

Failed to start dev preview.

Environment

  • App name: Image Search

  • Dev store: image-search-dev.myshopify.com

  • Shopify CLI: 3.92.0

  • Node: 25.8.1

  • Running command:
    shopify app dev --use-localhost --reset --verbose

Extension details

This is an Admin UI extension.

Current target / module:

  • target: admin.product-details.action.render

  • module: ./src/ActionExtension.jsx

The extension does build successfully before preview fails.

What I’ve already tried

  • Updated Shopify CLI

  • Confirmed Node is already newer than the versions mentioned in the related preview-failure thread

  • Ran shopify app deploy

  • Ran shopify app dev clean

  • Used --reset

  • Used --use-localhost

  • Uninstalled and reinstalled the app from the dev store

  • Re-linked the local project to the existing app

  • Confirmed the extension target/module path are correct

  • Confirmed the failure is happening after build, during preview creation

Relevant request IDs

  • 23cf5632-35f3-4aef-9932-22e87f0b7fe1-1773270019

  • 11de64be-a6e7-4629-bfd9-8232007e36d7-1773269505

  • 679b8f94-20fb-44a7-b5f9-6d7d44116432-1773269328

Why I think this may be preview-side

The local extension build succeeds, and the failure consistently appears only at the hosted preview step on the dev store. So this does not currently look like a simple local syntax/build problem.

If anyone from Shopify can inspect those request IDs or advise on what preview/runtime condition is failing, I’d really appreciate it.

Thanks.

1 Like
2

Hey @Wyatt_Parkins, looked into those request IDs. I don’t see any obvious issues that stand out, but I do see some locale validation errors.

Check your locales/ folder: any translation keys in non-default locale files (like fr.json) have to also exist in your default locale (en.default.json). If there’s a key in fr.json that’s missing from en.default.json, that could be the problem.

If that doesn’t change anything, let me know and we can dig in further.

3

I got this error today as well when i made a bundle extension for my app. My solution was to fix the locale files of the liquid content as well as closing {% tagName %} tags properly.

If you have access to an AI coding agent, that will solve this 100 times faster. Give it the verbose logs so the AI can see where it breaks and it will investigate and fix it for you.
I had this done by Claude, but a free solution would be GitHub’s Copilot.

Try this command that worked for me:

My Claude Code told me to run the command:
shopify app dev --verbose 2>&1 | grep -A 20 "graphql.json"
Then it spitted out the exact error that was crashing it:
❌ Error└ [blocks/bundle.liquid] Invalid tag 'schema': unknown key 'presets'

1 Like