Mastodon Hashtag Discovery: How New Tags Are Promoted in Trends

You see the Trending section on your Mastodon home page and wonder how those hashtags got there. Some tags appear to be brand new while others have been around for days. Mastodon uses a combination of local and federated activity to decide which hashtags trend. This article explains the exact rules that govern hashtag discovery and trend promotion on Mastodon instances.

The trending system is not a popularity contest based on total post count. Mastodon applies time windows, moderation filters, and language detection to determine which tags appear. Understanding these mechanics helps you use hashtags more effectively so your content reaches a wider audience.

By the end of this article you will know how to check your instance trend settings, why some tags never trend, and how to craft hashtags that have a higher chance of being promoted.

How Mastodon Decides Which Hashtags Trend

Mastodon does not use a global algorithm like Twitter or Facebook. Each instance independently computes its own trending hashtags based on local data plus data it receives from federated instances. The system is designed to prevent spam, bot-driven campaigns, and vote manipulation.

The Core Metrics for Trending

Three main factors determine whether a hashtag appears in the Trends section:

• Unique account count: Mastodon counts the number of unique accounts using a hashtag, not the total number of posts. One account posting 100 times with the same tag does not push that tag into trends. At least 10 to 20 different accounts must use the tag within a rolling 24-hour window. The exact threshold is set by the instance administrator.
• Time decay: Older posts contribute less weight to the trend score. A hashtag that had high activity 12 hours ago but zero activity in the last hour will drop in the ranking. Mastodon applies a half-life decay model so fresh activity matters more.
• Language detection: Mastodon separates trending tags by language. A tag used primarily in English posts will not compete with tags used in Japanese posts. This prevents one language from dominating the trending list on multilingual instances.

Moderation and Approval Workflow

Instance administrators have the final say over which tags appear in trends. The system works in two modes:

• Auto-approve: Any hashtag that meets the activity threshold automatically appears in trends. The admin can later remove it if needed.
• Manual approval: Tags that meet the threshold are queued for review. An admin must manually approve each tag before it appears. This mode prevents controversial or spam tags from trending even if they have high activity.

Admins can also create a list of banned hashtags. Any tag on that list is permanently excluded from trends regardless of activity level.

Steps to Check and Configure Hashtag Trending on Your Instance

If you are an instance administrator you can adjust how hashtags trend. If you are a regular user you can still see which settings your instance uses. Follow these steps to inspect or change the trend configuration.

1. Open Administration > Server Settings > Trends
   Log in to your Mastodon admin account. Navigate to Preferences > Administration > Server Settings. Click the Trends tab in the left sidebar.
2. Check the trending tags toggle
   Look for the option labeled Enable trending tags. If this toggle is off, no hashtags will appear in the Trends section on your instance. Turn it on to allow trending.
3. Set the approval mode
   Below the toggle you will see a dropdown labeled Trending tag mode. Choose Auto-approve for immediate display or Manual review to queue tags for approval. If you choose Manual review you must periodically check the Pending tags list.
4. Review pending tags
   Scroll down to the Pending trending tags section. Each tag shows the number of unique accounts that used it in the last 24 hours. Click the Approve button next to any tag you want to promote. Click Reject to prevent it from trending.
5. Add a banned hashtag
   In the Banned hashtags text box type a hashtag without the hash symbol. Press Enter after each tag. Click Save changes at the bottom of the page. Banned tags will never appear in trends even if they meet activity thresholds.

Common Misunderstandings About Hashtag Discovery

My hashtag has 50 posts but it is not trending

The most common reason is that those 50 posts came from only 2 or 3 accounts. Mastodon requires a minimum number of unique accounts, often 10 or more. If one person posts 50 times with the same tag, the tag will not trend. You need other users to adopt the tag.

My tag trended yesterday but disappeared today

Trending tags operate on a rolling 24-hour window. If the tag had a burst of activity yesterday but no new posts in the last few hours, it will drop out. To keep a tag trending you need sustained activity from multiple accounts throughout the day.

I see a tag in trends but it has fewer posts than my tag

The trending algorithm considers the rate of activity, not the total count. A tag that received 20 posts from 15 accounts in the last hour will rank higher than a tag with 100 posts from 20 accounts spread over 24 hours. Freshness matters more than volume.

Mastodon Hashtag Discovery vs Legacy Social Platforms

Item	Mastodon	X / Twitter
Trending calculation	Per-instance, based on unique accounts and time decay	Global algorithm using engagement velocity and geographic signals
Moderation control	Admins can approve, reject, or ban tags manually	Centralized team curates trends with limited public override
Language separation	Trends are separated by detected language	Trends are separated by country/region, not language
Minimum account threshold	Configurable, typically 10–20 unique accounts	Not publicly documented, varies by region
Bot prevention	Bots can post but do not boost trend score if accounts are not unique	Bot accounts are filtered by behavioral detection

Mastodon gives instance administrators direct control over what trends. The platform prioritizes distributed moderation over a single global list. This design prevents coordinated spam campaigns from dominating trends across all instances.

To get the most out of hashtag discovery, encourage other users to adopt your tag. Post at different times of the day so the activity window stays fresh. Check your instance trend settings to see if manual approval mode is active. If it is, ask your admin to approve your tag after it meets the unique account threshold.