"shopify app dev" breaks with new theme app extension

Shopify CLI and Libraries
,
1

I have reproduced the issue on the latest CLI version.

Yes, I am on the latest version

I have searched existing posts and this report is not a duplicate.

Yes, this isn’t a duplicate

In which of these areas are you experiencing a problem?

App
Extension

Expected behavior

“shopify app dev” runs after installing new extension with no modifications

Actual behavior

crashes with error:
Unexpected end of JSON input

Screenshot 2026-07-10 at 3.07.42 PM
Screenshot 2026-07-10 at 3.07.42 PM954×257 37.9 KB

not sure when this could have started happening, other types of extensions within the same app works fine (3 function (cart transform, checkout validation, discount extensions))

Reproduction steps

  • run “shopify app generate extension” > give name and choose theme app extension, no modifications whatsoever

  • run shopify app dev, get JSON error

  • removing the extension and running “shopify app dev”, runs with no issues

Verbose output

last two lines from running shopify app dev --verbose before the crash:

2026-07-10T22:02:08.747Z: Reusing crawler signature “Shopify CLI” for xxxx.myshopify.com (present: Signature, Signature-Input, Signature-Agent; missing: none).
2026-07-10T22:02:08.978Z: Request to https://xxxx.myshopify.com/admin/api/2026-07/graphql.json completed in 240 ms

Operating system

MacOS / shopify-cli via homebrew

CLI version

4.4.0

Shell

zsh

Nodejs version

v23.9.0

What language and version are you using in your application?

js?

2

Hi!

For a second I thought you shipped a fix in 4.5.0 but no, still broken.

As a quick test, I was able to recreate the issue on a fresh new install.

  1. shopify app init (react router app / js / npm)
  2. shopify app generate extension (cart transformer / js)
  3. shopify app generate extension (cart-checkout validation / js)
  4. shopify app generate extension (discounts / js)
  5. shopify app dev > app runs
  6. shopify app generate extension (theme app extension)
  7. shopify app dev > app crashes during init
  8. rm -rf theme app extension > shopify app dev > app runs
3

One last followup, you don’t even need to install the 3 cart transform functions. You can skip steps 2 - 4 and still end up with the same result.

4

running shopify app dev --verbose

here is the very last request ID before the crash:
Request to https://xxx.myshopify.com/admin/api/2026-07/graphql.json
x-request-id: 49dd6c61-109b-4322-8ee8-e784cdf80770-1783963788

5

I also uninstalled homebrew shopify-cli and installed two different versions of shopify-cli via npm with the same exact results, am i going crazy? this makes no sense.

npm i -g @shopify/cli@latest
and
npm i -g @shopify/cli@3

6

Ok, I was able to solve this thanks to Google Gemini, (Shopify’s AI assistant kept crashing every time i tried to post the file that generated the error).

The config file within ~/Library/Preferences/shopify-cli-theme-conf-nodejs was empty, causing that “Unexpected end of jSON input” error.

I added an empty object to the file, saved it. Ran shopify app dev from my original app, this time I was asked for the dev store’s preview password and it then stored a value into this config file and also ran the app with no further issues. so this was probably some weird config hiccup specifically happening on my dev store and from my local dev env due to that empty config.json file.

ughh, i don’t even know how that file was even empty to begin with but its working now.