Difference between npm install and npm ci

The main differences between using npm install and npm ci are:

The project must have an existing package-lock.json or npm-shrinkwrap.json.

If dependencies in the package-lock do not match those in package.json, npm ci will exit with an error, instead of updating the package-lock.
npm ci can only install entire projects at a time: individual dependencies cannot be added with this command.

If a node_modules is already present, it will be automatically removed before npm ci begins its install.

It will never write to package.json or any of the package-locks: installs are essentially frozen.