INCIDENT RUNBOOK

Fix: Env Variable Undefined At Build in Nuxt on Vercel

Comprehensive architectural post-mortem and verified configuration patch for nuxt deployed in vercel production environments.

Automated Remediation ProtocolUpdated for 2026 Production

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● Observed Terminal Error / Stack Trace

ERROR in./pages/index.vue
Module Error (from./node_modules/vue-loader/lib/loaders/templateLoader.js):
ReferenceError: process.env.MY_VARIABLE is not defined

Root Cause Analysis

The error occurs because Vercel builds the Nuxt application at build time, but the environment variables are not available during this phase. By default, Nuxt expects environment variables to be defined at runtime, not build time. This incompatibility arises from the discrepancy between the build and runtime environments, where the environment variables are not propagated correctly, leading to undefined variables in the Nuxt application.

● Configuration & Code Resolution

To resolve this issue, update the `vercel.json` configuration file to include the environment variables at build time. Add the following configuration:
--- vercel.json
+++ vercel.json
@@ -1,4 +1,6 @@
 {
   "version": 2,
+  "builds": [
+    { "src": "nuxt.config.js", "use": "@vercel/static-build" }
+  ],
   "env": {
+    "MY_VARIABLE": "@env.MY_VARIABLE"
   }
 }
Then, in your `nuxt.config.js` file, make sure to use the `process.env` object to access the environment variables:
--- nuxt.config.js
+++ nuxt.config.js
@@ -1,4 +1,6 @@
 export default {
   //... other configurations...
+  env: {
+    MY_VARIABLE: process.env.MY_VARIABLE
+  }
 }
Finally, ensure that the environment variable `MY_VARIABLE` is defined in your Vercel project settings.

Verification & Build Command

Run `vercel build` and `vercel deploy` to verify that the environment variables are correctly propagated and the Nuxt application builds without errors. Then, use `vercel logs` to inspect the runtime logs and ensure that the environment variables are accessible in the application.