Read-only verification of one environment variable in an existing deployment

Hi Vercel team,

Is there a supported read-only way to verify the value of one environment variable bound to a specific existing deployment? I need the deployment-specific value rather than the value currently saved in Project Settings.

I want to avoid redeploying, changing settings, calling the application or retrieving other variables.

What do env and build.env in the Get Deployment response represent? Can they establish the value bound to that deployment?

If no public API or dashboard option supports this, can support verify a single variable from a deployment snapshot? What information is required? Would it cover build-time configuration, runtime configuration or both? A documentation link would help.

This is a general question about supported methods, not a request to inspect an account. No resource IDs or variable values are included. Thank you.

I checked this on a throwaway project, so I can answer the env / build.env part at least.

In GET /v13/deployments/{id}, both env and build.env are arrays of variable names only, no values. On my test deployment env listed PROBE_VAR alongside the system VERCEL_* names, and build.env was the same list. So they tell you which variables were bound to that deployment, but not what they were set to.

They also can't be inferred from Project Settings, because a deployment keeps the value it was built with. I deployed with PROBE_VAR set to a 15-character value, then changed it in the project to a 5-character one without redeploying. A function on the existing deployment still reported length 15.

The closest read-only check I found is comparing timestamps. GET /v10/projects/{projectId}/env returns createdAt and updatedAt for each variable (the value itself comes back encrypted), and the deployment has createdAt. If the variable's updatedAt is earlier than the deployment's createdAt, the deployment was built from the value currently saved in settings (for that target and branch). If updatedAt is later, the deployment is holding an older value and the settings no longer tell you what it is. That doesn't involve redeploying, changing anything, or calling your app, but it only tells you "same as current" or "drifted", not the old value itself.

Getting the actual value bound to an old deployment would need Vercel support, so I'd leave that part to staff.