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You can add or edit an environment variable after deployment, but saving it usually does not update the deployment already serving traffic. Set the value in the right project or service and deployment environment, then perform the host’s required activation step: redeploy on Vercel, build and deploy on Netlify, or choose a save-and-deploy option on Render.
Before changing a variable: identify the deployment that needs it
First confirm which project or service is serving the affected app and which deployment context it uses. A host may keep separate values for production, preview, a branch, development, or a custom environment. Updating the wrong context can leave the live app unchanged even when the key appears in the dashboard.
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Also note whether your application reads the variable during its build or while it runs. If a frontend value is incorporated into built files, a new build may be needed to change what users receive. The exact behavior depends on the framework and host.
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Vercel: edit the project setting, then redeploy
- In the Vercel dashboard, select the project and open Settings > Environment Variables.
- Add the variable’s name and value, or use the menu beside an existing variable’s name to edit it. Select the environment or environments where it should apply, such as Production, Preview, Development, or a custom environment, then save.
- Redeploy the project. Vercel says changed values apply to new deployments; an existing deployment retains the values it had when created. See Vercel’s environment-variable documentation.
If the application still sees the value as undefined, check that the variable is assigned to the environment used by the deployment and that the redeployment completed. Vercel also documents framework-specific naming requirements; for some frameworks, a browser-facing variable needs a public prefix such as NEXT_PUBLIC_. Vercel’s project-variable guidance describes this example.
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Netlify: update the variable and build and deploy
- Open Project configuration > Environment variables.
- Filter for the key, select the variable, then choose Options > Edit. Add a variable if the key is not present.
- Check that the value applies to the deploy context serving the affected site, then run a build and deploy. Netlify says environment-variable changes require a build and deploy to take effect. See Netlify’s environment-variable guide.
Netlify also supports shared variables and values that differ by deploy context. If the deployed app continues to use an old value, verify the context associated with that deploy as well as the new build.
Render: choose whether to rebuild, deploy the existing build, or wait
- Open the service’s Environment page.
- Add or edit the key and value.
- Select the save action that matches the change: Save, rebuild, and deploy creates a new build and deploy; Save and deploy deploys the existing build with the updated values; Save only stores the change without deploying, so the service will not use it until a later deploy. Render documents these options in Environment Variables and Secrets.
Choose a rebuild when the updated value must be included in build output. Deploying the existing build may suit a change used only when the service runs, but whether that is sufficient depends on how the app consumes the variable.
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Why a saved variable may not appear in the app
- The deployment is still using its original settings. Saving a value and activating it are separate steps on these platforms. Complete the required redeploy or build-and-deploy action.
- The value is set in the wrong context. Confirm the affected deployment is using the project, service, branch, or deploy environment you changed.
- The key does not match the code. Check spelling, punctuation, and capitalization. Environment-variable names are commonly case-sensitive, though the platform documentation cited here does not establish casing rules for every host.
- The framework expects a particular name or prefix. Check the framework’s rules, especially for values intended for browser-side code. A public prefix indicates that a value may be exposed to users.
- The app reads the value at a different stage. A variable used during a frontend build may require rebuilding; a value read at runtime may follow a different activation path. Consult the host and framework instructions for your setup.
Keep secrets out of browser-facing variables
Do not put passwords, private API keys, or other secrets in variables intended for client-side code. A public prefix such as Vercel’s NEXT_PUBLIC_ example signals that the value can be exposed in the browser. Keep secrets in server-side configuration and verify the framework’s rules before exposing any variable.
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Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.What to check on other hosting platforms
The steps above are documented for Vercel, Netlify, and Render; they do not establish a universal procedure for every host, container platform, or self-managed server. Look for the provider’s service or project environment settings and confirm whether a change requires a rebuild, deployment, or process restart. Do not assume that saving a variable alone updates a running application.
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