docs.waku.org/docs/overview/concepts/content-topics.md

---
title: Content Topics
---

`Content Topics` are metadata strings set by developers on outgoing messages to facilitate protocol-level features like selectively processing incoming messages ([Relay](/overview/concepts/protocols#relay) or [Filter](/overview/concepts/protocols#filter)) and retrieving historical messages ([Store](/overview/concepts/protocols#store)) that meet specific filtering criteria. Please refer to the [WAKU2-TOPICS](https://rfc.vac.dev/spec/23/#content-topics) specification to learn more.

## Content Topic Format

Here is the recommended format for content topics:

`/{application-name}/{version}/{content-topic-name}/{encoding}`

- `application-name`: This is the unique name of your decentralized application (dApp) to prevent conflicts with other dApps.
- `version`: Typically starting at `1`, this field helps track breaking changes in your messages.
- `content-topic-name`: The specific name of the content topic used for filtering.
- `encoding`: The message serialization/encoding format, with [Protocol Buffers](https://protobuf.dev/) (`proto`) being the recommended choice.

For instance, if your dApp is called `SuperCrypto` and it allows users to receive notifications and send private messages, you can consider using the following content topics:

- `/supercrypto/1/notification/proto`
- `/supercrypto/1/private-message/proto`

:::info
While you can choose any encoding format for your `Content Topic`, we highly recommend using Protocol Buffers (`proto`) because of its efficiency. Choosing a lightweight format ensures optimal performance of your dApp.
:::

## Naming Considerations

When choosing a content topic, it is crucial to consider privacy implications. The `Filter` protocol discloses content topics to peers, and the `Store` protocol can link them with a light node, allowing nodes providing these services to access message content topics, posing potential privacy risks.

:::info
Waku is developing privacy-preserving features like [Anonymous Filter Subscription](https://rfc.vac.dev/spec/12/#future-work) for the `Filter` protocol and [Anonymous Query](https://rfc.vac.dev/spec/13/#future-work) for the `Store` protocol to hide content topics from potential adversaries.
:::

You can preserve the anonymity of individual identities by increasing [k-anonymity](https://www.privitar.com/blog/k-anonymity-an-introduction/), where k is proportional to the network size (number of subscribers). This involves using a single content topic across the entire application or specific features such as notifications or private messages, allowing multiple users to share it.

However, maintaining functionality with a single content topic can introduce complexity. We recommend switching functionality using the Protocol Buffer message format or the [Waku Message](/overview/concepts/protocols#waku-message) `meta` attribute. By doing so, applications can retain a high granularity and functionality while using a single content topic, preserving user privacy.