Mastodon instance administrators and active users often rely on trending tags and relay servers to discover new content across the fediverse. Trending tags show which hashtags are most popular on a local instance or across the federated timeline. Relay discovery uses dedicated relay servers to pull in public posts from many instances at once. These two features serve different discovery goals and have different technical requirements. This article explains how trending tags and relay discovery work, how they differ, and when to use each approach.
Key Takeaways: Mastodon Trending Tags vs Relay Discovery
- Trending Tags (Preferences > Appearance > Show trending tags): Displays locally trending hashtags based on recent post volume on your instance and its federated timeline.
- Relay Discovery (Admin > Relays > Add Relay): Connects your instance to a relay server that forwards public posts from many other instances into your federated timeline.
- Trending Tags vs Relays: Trending tags show popularity of existing content; relays bring in new content from instances you have not manually followed.
How Mastodon Trending Tags Work
Mastodon trending tags are a built-in feature that surfaces hashtags with recent high activity. The algorithm counts how many unique users have posted with a given tag in the past 24 hours on your local instance and on instances your instance follows directly. The results appear in the Explore section under the Trending tab. Instance moderators can also pin specific tags to the sidebar. Trending tags do not require any server-side configuration from the admin. They work automatically once the instance has enough active users and federated connections.
The trending algorithm applies a decay factor so that a tag must sustain activity over time to remain in the top list. Tags with spam or abuse reports are automatically suppressed. Instance moderators can manually approve or reject specific tags from the trending list through the moderation interface. Trending tags are instance-scoped. What trends on one instance may not trend on another because each instance sees a different federation graph.
How Relay Discovery Works
A relay is a dedicated server that acts as a broadcast hub for public posts. When an instance subscribes to a relay, the relay sends all public posts it receives from its other subscriber instances to the subscribing instance. This allows a small or new instance to populate its federated timeline with content from hundreds of instances without manually following each one. The relay does not filter by topic or hashtag. It forwards all public posts from its connected instances.
Instance administrators add a relay by going to Administration > Relays and entering the relay server URL. The instance must then enable relay subscription for each relay. The relay must also accept the subscription request. Many relay operators require manual approval. Once connected, the instance will start receiving public posts from all other instances subscribed to that relay. The relay itself does not store posts. It only forwards them in real time.
Key Differences Between Trending Tags and Relay Discovery
Trending tags rely on existing content that has already been pulled into the instance through normal federation. Relay discovery proactively pulls in content from instances the admin has not manually followed. Trending tags show a ranked list of hashtags. Relay discovery shows no tags at all — it simply fills the federated timeline with new posts.
Trending tags are visible to all users on the instance. Relay discovery is invisible to end users. Users see the resulting posts in their federated timeline, but they have no direct control over which relays the instance uses. Trending tags require no admin action beyond enabling the feature. Relay discovery requires the admin to find, request, and maintain connections to relay servers.
Relay discovery introduces a moderation risk. If a relay forwards spam or illegal content, the instance must rely on its own moderation tools to filter it. Trending tags are less risky because they surface content that has already passed through the instance’s existing federation and moderation pipeline.
When to Use Trending Tags vs Relay Discovery
Use trending tags when you want to see what topics are currently popular among your instance’s existing federation circle. This is useful for content discovery within a known community. Use relay discovery when your instance is new, small, or isolated and you want to quickly populate the federated timeline with diverse content from many instances.
A combined approach works well for most instances. Keep trending tags enabled for everyday content discovery. Add one or two well-moderated relays to increase the instance’s reach. Avoid adding too many relays because each relay increases server load and moderation workload. Monitor the federated timeline after adding a relay to ensure the content quality meets your instance’s standards.
Common Misconceptions About Trending Tags and Relays
Trending tags show all posts with that tag
Trending tags only show a sample of recent posts. The full list of posts for a tag is available by searching the tag directly. Trending is a popularity indicator, not a complete archive.
Relays work like a search engine
Relays do not index or search content. They forward all public posts from subscriber instances without filtering. To search for specific topics, use the built-in Mastodon search or a separate search tool like Mastodon Search.
You must use relays to see content from other instances
This is false. Normal federation happens when a user on your instance follows a user on another instance. That follow pulls in that user’s public posts and boosts. Relays are an optional addition for administrators who want to accelerate content flow without waiting for individual follows.
Mastodon Trending Tags vs Relay Discovery: Feature Comparison
| Item | Trending Tags | Relay Discovery |
|---|---|---|
| Purpose | Show popular hashtags on the instance | Pull in public posts from many instances |
| User visibility | Visible in Explore > Trending | Invisible to end users |
| Admin configuration | None required (enabled by default) | Must add relay URL and accept subscription |
| Content source | Existing federated timeline and local posts | All subscriber instances of the relay |
| Moderation control | Moderators can approve or reject tags | No per-relay moderation; instance filters apply |
| Server load impact | Minimal | High for busy relays |
Trending tags and relay discovery serve different content discovery needs on Mastodon. Trending tags help users find popular topics within their existing federation graph. Relay discovery helps administrators fill the federated timeline with fresh content from outside that graph. Use trending tags for day-to-day topic exploration. Add relays only when your instance needs a broader view of the fediverse. Monitor both features regularly to maintain content quality and server performance.
To enable or disable trending tags, go to Preferences > Appearance and check or uncheck Show trending tags. To add a relay, go to Administration > Relays and enter a relay server URL such as relay.example.com. Start with a single relay from a trusted operator and review the federated timeline for one week before adding more. This balanced approach gives your instance the widest possible content discovery without overwhelming your moderation team or server resources.