---
title: "About Grafana Mimir tenant IDs | Grafana Mimir documentation"
description: "Learn about tenant ID restrictions."
---

# About Grafana Mimir tenant IDs

Within a Grafana Mimir cluster, the tenant ID is the unique identifier of a tenant. For information about how Grafana Mimir components use tenant IDs, refer to [Authentication and authorization](/docs/mimir/v2.17.x/manage/secure/authentication-and-authorization/).

## Restrictions

Tenant IDs must be less-than or equal-to 150 bytes or characters in length and can only include the following supported characters:

- Alphanumeric characters
  
  - `0-9`
  - `a-z`
  - `A-Z`
- Special characters
  
  - Exclamation point (`!`)
  - Hyphen (`-`)
  - Underscore (`_`)
  - Single period (`.`)
  - Asterisk (`*`)
  - Single quote (`'`)
  - Open parenthesis (`(`)
  - Close parenthesis (`)`)

> Note
> 
> For security reasons, `.` and `..` aren’t valid tenant IDs.

> Note
> 
> `__mimir_cluster` isn’t a valid tenant ID because Mimir uses the name internally.

All other characters, including slashes and whitespace, aren’t supported.