Mastodon Post Mentions Limit: How Many Per Post Before Throttling

When you compose a post on Mastodon and include multiple @mentions, the platform may refuse to send the post or silently drop notifications for some users. This happens because each Mastodon instance enforces a limit on the number of unique accounts you can mention in a single post. Exceeding this limit triggers throttling, which can prevent the post from being delivered or cause it to be rejected by remote servers. In this article, you will learn the exact mention limit per post, why instances enforce this rule, and how to work around the restriction without losing communication.

Why Mastodon Limits Mentions Per Post

Mastodon is built on ActivityPub, a decentralized protocol that requires each post to be delivered individually to every mentioned user’s server. If a post includes 50 mentions, the sending instance must send 50 separate delivery requests to potentially 50 different instances. This creates a heavy load on the sending server and on the receiving servers, which must each process the incoming post and notify the mentioned user.

The mention limit is a spam and abuse prevention measure. Without it, a malicious user could mention thousands of accounts in a single post, causing a denial-of-service attack against the sending instance and all recipient instances. The limit also prevents accidental abuse where a user might copy a large mailing list into a post and flood dozens of servers with unwanted notifications.

The default limit of 10 mentions per post is defined in the Mastodon source code under the MAX_MENTIONS_PER_POST constant. Instance admins can override this value by editing the .env.production file and adding the line MAX_MENTIONS_PER_POST=20 or any other integer. However, most admins keep the default because raising it increases the risk of server overload and spam.

How to Check and Work Around the Mention Limit

If you need to notify more than 10 people in a single post, you have two main options: split the post into multiple posts or ask your instance admin to raise the limit. Below are the exact steps for each method.

Method 1: Split Mentions Across Multiple Posts

1. Count your mentions before posting
   In the compose box, count every unique @username you have typed. Mastodon counts each unique account only once, even if you mention the same person multiple times. If the count exceeds 10, you must split the list.
2. Create a first post with the first 10 mentions
   Write the main body of your message and include the first 10 unique @mentions. Post this message normally.
3. Reply to your own post with the remaining mentions
   Immediately reply to the first post with the next group of mentions. Continue replying until all recipients are covered. Each reply counts as a new post with its own mention limit of 10.
4. Use a content warning to group mentions
   If you want to keep the thread tidy, add a content warning such as “Group notification thread” to each reply. This hides the post body behind a clickable warning and reduces visual clutter in followers’ timelines.

Method 2: Request a Higher Limit from Your Instance Admin

1. Locate your instance admin contact
   Go to Preferences > Administration > About. Look for the “Admin” or “Contact” section. Many instances list an email address or a Mastodon account for the admin.
2. Send a direct message or email explaining your need
   Explain that you need to mention more than 10 people in a single post for a legitimate purpose, such as coordinating a group announcement or an event reminder. Be specific about how many mentions you need and how often you will use the higher limit.
3. Wait for the admin to adjust the setting
   The admin must edit the .env.production file on the server, add or change the line MAX_MENTIONS_PER_POST=20 (or your desired number), and restart the Mastodon services. Once the change is applied, you can post with up to the new limit.

Common Issues When Mentioning Multiple Accounts

Mastodon Shows “Too many mentions” Error

This is the most common symptom of hitting the mention limit. The Mastodon web interface displays a red error banner below the compose box saying “Too many mentions” or “Validation failed: Mentions limit reached.” The post is not sent. To fix this, remove enough @mentions until the count drops to 10 or below. If you need all recipients, use the split method described above.

Some Mentions Are Not Delivered Even Under the Limit

If you stay within the 10-mention limit but some recipients still do not receive a notification, the issue is likely not the mention limit. Check that the recipient’s instance is not defederated from yours. Also verify that the recipient has not muted or blocked you. If the problem persists, try mentioning the account using its full @username@instance.tld format instead of just @username.

Mentions in Content Warnings Also Count Toward the Limit

Some users assume that mentions placed inside the content warning field are exempt from the limit. This is not true. Mastodon counts all unique @mentions in the entire post, including the CW text and the post body. If you hide mentions in the CW, they still count toward the 10-mention cap.

Mastodon Mention Limit vs Other Platforms

Item	Mastodon	Twitter / X
Default mention limit per post	10 unique accounts	50 unique accounts
Can admin raise the limit?	Yes, by editing server config	No, limit is hardcoded
Throttling behavior when exceeded	Post is rejected with error message	Post is rejected with error message
Mentions in replies count separately	Yes, each reply has its own limit	Yes, each reply has its own limit
Visible vs hidden mentions	All mentions count, even in CW	All mentions count, even in alt text

Mastodon’s limit is more restrictive than Twitter’s by default, but the ability for instance admins to raise the limit gives Mastodon more flexibility for communities that need to coordinate large group announcements.

You now know that Mastodon limits each post to 10 unique mentions by default and that you can work around it by splitting mentions across replies or asking your admin to raise the limit. If you frequently need to notify large groups, consider using a dedicated announcement account or a shared list that followers can subscribe to. One advanced tip: you can create a private list of accounts and then mention the list name using a bot or custom script, though this requires programming and is not supported natively in Mastodon.