Mastodon Hashtag Trending Algorithm: How Topics Get Promoted

Mastodon displays trending hashtags on the Explore page, but the way topics get promoted differs from Twitter or Facebook. You might have noticed that some hashtags appear in Trending while others never show up, even if they seem popular in your local timeline. This happens because Mastodon uses a decentralized algorithm that filters trending content based on account reputation, language, and server-level settings. This article explains exactly how the Mastodon hashtag trending algorithm works, what factors determine promotion, and how instance moderators can adjust trending behavior.

Why Mastodon Does Not Use a Global Trending Algorithm

Mastodon is a federated network made of independent instances, each with its own rules and moderation policies. A global trending algorithm would require central coordination and could be gamed by spam accounts. Instead, each instance calculates its own trending hashtags based on local data and server-wide settings. This means the trending list you see on one instance can be completely different from the list on another instance, even for the same hashtag.

The algorithm evaluates three main factors: recency, account reputation, and reach. Recency means the hashtag must have been used in the past 24 hours to qualify. Account reputation prevents new or low-engagement accounts from artificially boosting a topic. Reach measures how many distinct accounts used the hashtag, not just the total number of posts. A hashtag used by 100 different accounts is more likely to trend than a hashtag used 500 times by the same five accounts.

How Account Reputation Affects Trending

The Mastodon server tracks the age of each account and the number of followers it has. Accounts that are less than 30 days old or have fewer than 10 followers are considered low-reputation. Posts from low-reputation accounts still appear in timelines, but their hashtags are less likely to enter the trending pool. This prevents bot networks from creating fake trends by mass-posting the same hashtag from newly created accounts.

The Role of Language Detection

Mastodon automatically detects the language of each post using its built-in language detection library. Hashtags are grouped by language before ranking. If your instance has a majority of English-speaking users, you will see English trending hashtags first. To view trending hashtags in another language, you must switch your language filter in the Explore page. This language grouping prevents a single language from dominating the trending list on multilingual instances.

Steps to View and Understand Trending Hashtags on Your Instance

1. Open the Explore page
   Click the Explore icon (compass symbol) in the left sidebar or navigate to the Explore tab on the Mastodon web interface.
2. Click the Hashtags tab
   On the Explore page, select the Hashtags tab. You will see a list of trending hashtags with a small graph icon next to each one showing recent usage activity.
3. Check the trending score
   Each hashtag shows a percentage score representing how much its usage has increased compared to the previous 24 hours. A score of +150% means the hashtag is being used 1.5 times more than yesterday.
4. Click any hashtag to see related posts
   Clicking a hashtag opens a filtered view showing all public posts that include that hashtag. You can see which accounts are driving the trend and what kind of content is being posted.
5. Switch language filter to see other trends
   Click the language dropdown at the top of the Hashtags tab. Select a different language to view trending hashtags from that language group.

If Trending Hashtags Are Not Showing Up as Expected

Trending feature is disabled on your instance

Instance moderators can disable trending entirely through the admin panel. If you see no trending hashtags at all, the feature may be turned off. Check with your instance admin or look for a message saying “Trending is disabled on this server.” There is no user-side fix for this restriction.

Hashtag usage is too low or too recent

A hashtag must be used by at least 10 different accounts within 24 hours to qualify for trending. If you are trying to promote a niche topic, it may not meet the minimum threshold. Additionally, the algorithm updates every 15 minutes, so a hashtag may appear after a short delay once it reaches the threshold.

Low-reputation accounts are using the hashtag

If most posts using a hashtag come from accounts less than 30 days old or with fewer than 10 followers, the hashtag will not trend. To fix this, encourage established accounts with higher follower counts to use the hashtag. The algorithm weights posts from older, more connected accounts more heavily.

Language filter is set to the wrong language

If you are looking for trending hashtags in a language different from your instance default, you must manually switch the language filter. Click the language dropdown on the Explore page and select the correct language. The trending list will update immediately.

Item	Local-only trending	Federated trending
Scope	Only posts from users on the same instance	Posts from all instances federated with your server
Default setting	Enabled on most instances	Enabled on most instances
Moderation control	Admins can disable local trending	Admins can disable federated trending
Use case	Small communities want to see internal trends first	Large instances want to surface global conversations

Mastodon’s trending algorithm is designed to surface organic, community-driven topics while resisting spam and manipulation. By understanding the reputation thresholds and language grouping, you can better predict which hashtags will trend on your instance. If you are a moderator, you can fine-tune trending behavior through the admin settings to match your community’s needs. Try adjusting the minimum account age for trending eligibility to see how it changes the trending list over a week.