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The playground has a single required environment variable. It tells the Next.js backend where the quasar quantum simulator service is running on Google Cloud Run. Without it, every API call returns an error.

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GOOGLE_CLOUD_SERVICE_URL

The base URL of the deployed quasar service on Google Cloud Run.

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Format

For example:
Google Cloud Run generates this URL when you deploy the service. You can find it in the Cloud Run console under the service’s detail page, listed as the service URL.

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What it controls

All four API endpoints in the playground use this variable to forward requests to the quasar gRPC-transcoded service. Internally, each endpoint constructs a request to:
Where <Method> is one of Simulate, Share, Edit, or Validate.

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What happens if it is not set

If GOOGLE_CLOUD_SERVICE_URL is missing, every API call returns an HTTP 500 response with the following body:
The playground UI will show an error in the results panel when you try to run, share, or load any program.

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How to set it in Vercel

1

Deploy quasar to Google Cloud Run

Follow the quasar deployment instructions to deploy the simulator service. Copy the service URL from the Cloud Run console once deployment completes.
2

Open your Vercel project settings

In the Vercel dashboard, navigate to your qasm-playground project and click Settings, then Environment Variables.
3

Add the variable

Set the variable name to GOOGLE_CLOUD_SERVICE_URL and paste the Cloud Run service URL as the value. Apply it to the Production environment (and optionally Preview).
4

Redeploy

Trigger a new deployment so Vercel picks up the new variable. The playground will use it immediately after the deployment completes.
Do not expose this URL in client-side code. The variable is read only on the server inside Next.js API routes (app/api/*/route.ts), so it is never sent to the browser.