Mastodon is a decentralized social network made up of thousands of independent servers called instances. Each instance hosts its own users and content, which can make finding posts from other instances feel difficult. A hashtag search in Mastodon does not limit results to just your home instance. Instead, it fetches public posts from every federated instance that your server knows about. This article explains how to search Mastodon across instances by hashtag, how the federated search works, and what to do when results appear incomplete.
Key Takeaways: Searching Hashtags Across All Federated Mastodon Instances
- Hashtag search bar or Explore > Hashtags: Enter a hashtag without the # symbol to see public posts from all federated instances your server follows.
- Instance admin settings for full-text search: Enable Elasticsearch on the server to allow keyword search beyond just hashtags and usernames.
- Following remote accounts manually: Use the search bar to find a user on another instance, then follow them to pull their future hashtagged posts into your federated timeline.
Mastodon Federated Search and Hashtag Visibility
Mastodon does not have a global search engine like Twitter or Bluesky. Instead, it uses a federated model where each instance stores only the posts it has seen. When you search for a hashtag, your instance looks through its local database of posts from users on your instance plus posts from any federated instance it has encountered. This means the results you see depend entirely on which instances your server has already connected with.
A hashtag search in Mastodon includes three sources:
- Local timeline: Posts from users on your own instance that use the hashtag.
- Federated timeline: Posts from remote instances that your server has received, either because someone on your instance follows a user on that remote instance or because the remote instance is publicly federated.
- Trending hashtags: Hashtags that have gained traction across the fediverse, surfaced by your instance based on activity.
If a remote instance has not yet federated with yours, its posts will not appear in your hashtag search. This is not a bug. It is a core design choice of Mastodon. The search is always a subset of the entire fediverse.
Steps to Search Mastodon Across Instances by Hashtag
Follow these steps to search any hashtag across federated instances from the Mastodon web interface or any official mobile app. The process is identical across all Mastodon versions 4.0 and later.
- Open the search bar
Click or tap the search icon at the top of the Mastodon interface. On the web version, it appears as a magnifying glass in the left sidebar or at the top center of the screen. On mobile, it is usually at the top of the Home or Explore tab. - Type the hashtag without the # symbol
Enter the hashtag text only. For example, typephotographynot#photography. Mastodon automatically treats the input as a hashtag search if it matches a known tag. Press Enter or tap the search icon. - Review the search results
The results page shows a dedicated Hashtags section at the top. Click or tap the hashtag entry to view all public posts tagged with that hashtag from your instance and all federated instances. The posts appear in reverse chronological order. - Use Explore > Hashtags as an alternative
If you prefer browsing trending or popular hashtags, go to the Explore tab and select Hashtags. Mastodon displays a list of hashtags currently trending on your instance. Click any hashtag to see federated results for that tag. - Follow a hashtag to keep it in your timeline
On the hashtag page, click the Follow button. Mastodon will add posts using that hashtag to your Home feed as they appear from federated instances. This works even if you do not follow any users who use that tag. - Search for a specific instance manually
If you know a hashtag is popular on a particular instance, type the full URL of that instance followed by the hashtag. For example, enterhttps://mastodon.social/tags/photographyinto your browser. This opens that instance’s public hashtag page, which may show posts not yet federated to your instance.
Common Limitations and Workarounds for Hashtag Search
Hashtag Search Returns No Results or Very Few Posts
If a hashtag returns zero results or only a handful, your instance has not yet federated with instances where that hashtag is active. To fix this, search for a user on a popular instance like mastodon.social who posts about that topic. Follow that user. Their instance will then begin sending posts to your server, and future hashtagged posts from that instance will appear in your search results.
Hashtag Search Shows Only Local Posts Despite Many Remote Posts Existing
This happens when your instance has limited federation. Check your instance’s federation settings if you are an admin. If you are a regular user, the only workaround is to manually follow users on instances that discuss your topic. Each follow expands your server’s view of the fediverse.
Cannot Search for Keywords Inside Posts, Only Hashtags
By default, Mastodon does not support full-text search of post content. The search bar matches hashtags, usernames, and URLs. If you need to search inside posts, ask your instance admin to enable Elasticsearch. This adds full-text search capability. Without Elasticsearch, you must rely entirely on hashtags to find relevant content.
Hashtag Results Are Not Real-Time
Mastodon updates hashtag results as new posts arrive from federated instances. There is no manual refresh button for hashtag pages. If you do not see a post that was just published on a remote instance, wait a few seconds and reload the page. Federation delays are normal, especially for instances with low bandwidth or high load.
Mastodon Hashtag Search vs Full-Text Search
| Item | Hashtag Search | Full-Text Search (Elasticsearch) |
|---|---|---|
| What it searches | Only posts tagged with the exact hashtag | Any word in the post content, media descriptions, or profile fields |
| Requires server setup | No configuration needed — works on every instance | Instance admin must install and configure Elasticsearch |
| Scope of results | Local and federated posts from known instances | Local and federated posts from known instances |
| Speed | Instant — database is indexed by tag | Fast but depends on Elasticsearch cluster size |
| User control | Add any hashtag to your posts to make them discoverable | Users can opt out via Settings > Privacy > Include posts in search |
Hashtag search is the primary discovery tool on Mastodon. Full-text search is a supplement that many small instances do not have. For the broadest reach, always include relevant hashtags in your posts. This ensures your content appears in hashtag searches across all federated instances, regardless of whether those instances have full-text search enabled.