next.js/errors/env-key-not-allowed.md

# The key "<your key>" under "env" in next.config.js is not allowed.

#### Why This Error Occurred

Next.js configures internal variables for replacement itself. These start with `__` or `NODE_`, for this reason they are not allowed as values for `env` in `next.config.js`

#### Possible Ways to Fix It

Rename the specified key so that it does not start with `__` or `NODE_`.
Block Certain Env Keys That Are Used Internally (#6260) Closes: #6244 This will block the following keys: ``` NODE_.+ __.+ ``` There doesn't seem to be a way to simulate a failed build or else I'd add tests for it. 2019-02-15 16:49:40 +00:00			`# The key "<your key>" under "env" in next.config.js is not allowed.`

			`#### Why This Error Occurred`

			Next.js configures internal variables for replacement itself. These start with `__` or `NODE_`, for this reason they are not allowed as values for `env` in `next.config.js`

			`#### Possible Ways to Fix It`

			Rename the specified key so that it does not start with `__` or `NODE_`.