»"Dev" Server Mode

You can start Vault as a server in "dev" mode like so: vault server -dev. This dev-mode server requires no further setup, and your local vault CLI will be authenticated to talk to it. This makes it easy to experiment with Vault or start a Vault instance for development. Every feature of Vault is available in "dev" mode. The -dev flag just short-circuits a lot of setup to insecure defaults.

Warning: Never, ever, ever run a "dev" mode server in production. It is insecure and will lose data on every restart (since it stores data in-memory). It is only made for development or experimentation.

»Properties

The properties of the dev server (some can be overridden with command line flags or by specifying a configuration file):

Initialized and unsealed - The server will be automatically initialized and unsealed. You don't need to use vault operator unseal. It is ready for use immediately.
In-memory storage - All data is stored (encrypted) in-memory. Vault server doesn't require any file permissions.
Bound to local address without TLS - The server is listening on 127.0.0.1:8200 (the default server address) without TLS.
Automatically Authenticated - The server stores your root access token so vault CLI access is ready to go. If you are accessing Vault via the API, you'll need to authenticate using the token printed out.
Single unseal key - The server is initialized with a single unseal key. The Vault is already unsealed, but if you want to experiment with seal/unseal, then only the single outputted key is required.
Key Value store mounted - A v2 KV secret engine is mounted at secret/.

»Use Case

The dev server should be used for experimentation with Vault features, such as different auth methods, secrets engines, audit devices, etc. If you're new to Vault, you may want to pick up with Your First Secret in our getting started guide.

In addition to experimentation, the dev server is very easy to automate for development environments.