---
source_url: https://www.pubnub.com/docs/general/basics/identify-users-and-devices
title: Identify users and devices
updated_at: 2026-05-25T11:26:05.154Z
---

> Documentation Index
> For a curated overview of PubNub documentation, see: https://www.pubnub.com/docs/llms.txt
> For the full list of all documentation pages, see: https://www.pubnub.com/docs/llms-full.txt


# Identify users and devices

Set a User ID in your client setup to connect to PubNub. Use a UTF-8 string up to 92 characters.

User IDs must be unique per app as they identify the client. The client can be an end user, device, or server. One person can use many devices (phone, tablet, laptop). See [the relationship between users and devices](https://www.pubnub.com/docs/general/setup/users-and-devices). PubNub Presence uses User IDs to track online status in real time.

User IDs also support billing and analytics.

:::tip Filter by message publisher
You can use User IDs to filter messages by publisher using server-side [subscribe filters](https://www.pubnub.com/docs/general/channels/subscribe-filters).
:::

User IDs help [calculate your bill](https://www.pubnub.com/docs/general/setup/account-setup#pricing-model) under the Monthly Active User (MAU) pricing model. An MAU is a unique user with a User ID who connects to PubNub at least once in a month and sends an API call. If you want to pay for [transactions](https://www.pubnub.com/pricing/transaction-classification/), consider transaction-based pricing.

:::note User ID / UUID
User ID is also referred to as **UUID/uuid** in some APIs and server responses but **holds the value** of the **userId** parameter you [set during initialization](https://www.pubnub.com/docs/general/setup/users-and-devices#set-the-user-id).
:::

After you create your account and configure the SDK, you can [start sending messages](https://www.pubnub.com/docs/general/basics/send-messages).

## Terms in this document

* **User** - An individual or entity that interacts with a system, application, or service. In PubNub, a user typically refers to someone who sends or receives messages through the platform, identified by a unique user ID or username.
* **User ID** - UTF-8 encoded, unique string of up to 92 characters used to identify a single client (end user, device, or server) that connects to PubNub.