For Unleash to be of any use, it requires at least a server and a [consuming client](../sdks/index.md). More advanced use cases may call for multiple clients, automated feature toggle updates, the [Unleash proxy](../sdks/unleash-proxy.md) and [Unleash proxy clients](../sdks/index.md#front-end-sdks), and more. To facilitate communication between all these moving parts, Unleash uses a system of API tokens and client keys, all with a specific purpose in mind.
This section describes what API tokens are. For information on how to create them, refer to the [how-to guide for creating API tokens](../user_guide/token.mdx).
All types use [the same format](#format) but have different intended uses. Admin and client tokens are _secrets_ and should _not_ be exposed to end users. Front-end tokens, on the other hand, are not secret.
### The parts of an API token {#token-data}
An API token contains the following pieces of information:
| Name | Description |
| --- | --- |
| Token name (sometimes called "username") | The token's name. Names or **not** required to be unique. |
| Type | What kind of token it is: admin, client, or front-end. |
| Projects | What projects a token has access to. |
| Environment | What environment the token has access to. |
**Admin tokens** grant _full read and write access_ to all resources in the Unleash server API. Admin tokens have access to all projects, all environments, and all global resources (find out more about [resources in the RBAC document](../user_guide/rbac.md#core-principles)).
**Client tokens** are intended for use in [server-side client SDKs](../sdks/index.md#server-side-sdks) (including the Unleash Proxy) and grant the user permissions to:
When creating a client token, you can choose which projects it should be able to read data from. You can give it access to a specific list of projects or to all projects (including projects that don't exist yet). Prior to Unleash 4.10, a token could be valid only for a _single project_ or _all projects_.
- [Front-end SDKs](../sdks/index.md#front-end-sdks). You will _not_ be able to connect to the Unleash server due to CORS restrictions. To connect front-end SDKs, choose one of the following options:
- Enable the [Unleash front-end API](./front-end-api.md) and create a [front-end token](#front-end-tokens).
- Configure an [Unleash Proxy](../sdks/unleash-proxy.md) and use [Proxy client keys](#proxy-client-keys).
### Front-end tokens
**Front-end tokens** are used with [front-end SDKs](../sdks/index.md#front-end-sdks) when used with the [Unleash front-end API](./front-end-api.md). They grant the user permission to:
- Read the enabled toggled for a given context
- Register applications with the Unleash server
- Send usage metrics
As with [client tokens](#client-tokens), front-end tokens can read data from one, multiple, or all existing projects.
Each front-end token is only **valid for a single environment**.
Use front-end tokens in:
- [Front-end SDKs (also known as _proxy clients_)](../sdks/index.md#front-end-sdks).
Do **not** use front-end tokens in:
- [Server-side SDKs](../sdks/index.md#server-side-sdks). The format is different, so they won't work correctly.
API tokens come in one of two formats. When we introduced [environments](../user_guide/environments.md) in Unleash 4.3, we updated the format of the tokens to provide more human-readable information to the user. Both formats are still valid (you don't need to update a working token of the old format) and are described below.
#### Version 1
The first version of API tokens was a 64 character long hexadecimal string. Example:
The parts are separated by two different separators: A colon (`:`) between the project(s) and the environment, and a full stop (`.`) between the environment and the hash.
- The id of a specific project, for example: `default`. This indicates that the token is **only valid for this project**.
- A pair of opening and closing square brackets: `[]`. This indicates that the token is **valid for a discrete list of projects**. The list of projects is not shown in the token.
- An asterisk: `*`. This indicates that the token is **valid for all projects (current and future)**.
Use proxy client keys to connect [Proxy client SDKs (front-end SDKs)](../sdks/index.md#front-end-sdks) to the [Unleash Proxy](../sdks/unleash-proxy.md). As opposed to the [API tokens](#api-tokens), Proxy client keys are _not_ considered secret and are safe to use on any clients (refer to the [the proxy documentation for more about privacy](../sdks/unleash-proxy.md#we-care-about-privacy)). They do _not_ let you connect to the Unleash server API.
Proxy client keys are arbitrary strings that you _must_ provide the Unleash proxy with on startup. They can be whatever you want and you **create them yourself**.
:::info Creating proxy client keys
To designate a string as a proxy client key, add it to the `clientKeys` list when starting the proxy, as mentioned in the [_configuration_ section of the Unleash proxy documentation](../sdks/unleash-proxy.md#configuration). Connecting clients should then specify the same string as their client key.
:::
Unleash does not generate proxy client keys for you. Because of this, they have no specific format.
