Mastodon and Sharkey are both part of the ActivityPub-fediverse, but they are not identical software. Mastodon users and Sharkey users often encounter unexpected behavior when interacting across instances. These issues range from missing reactions to broken content warnings. This article explains the key compatibility differences between Mastodon and Sharkey. It covers how federation works between the two platforms and lists specific features that do not transfer correctly.
Key Takeaways: Mastodon-Sharkey Federation Behavior
- ActivityPub protocol core: Both platforms use the same underlying protocol, so basic posts, boosts, and follows work across instances.
- Custom emoji reactions: Sharkey supports Misskey-style reactions, but Mastodon displays them as favorites or ignores them entirely.
- Content warnings and NSFW flags: Both platforms support content warnings, but formatting and visibility settings may not sync perfectly.
How Mastodon and Sharkey Federate
Mastodon and Sharkey both implement the ActivityPub standard. This means a user on a Mastodon instance can follow a user on a Sharkey instance and vice versa. Basic interactions like posting, boosting, and favoriting work across both platforms. The server-to-server communication uses JSON-LD payloads that both sides can parse.
However, Mastodon and Sharkey extend the ActivityPub protocol differently. Mastodon uses its own extensions for features like polls and content warnings. Sharkey inherits extensions from Misskey, which include custom emoji reactions, quote posts, and more granular visibility settings. When a Sharkey user posts a reaction that Mastodon does not understand, the Mastodon server either drops the reaction or converts it to a favorite. This can confuse users who expect to see the original reaction.
ActivityPub Version Differences
Mastodon currently implements ActivityPub 1.0 with some Mastodon-specific additions. Sharkey implements ActivityPub 1.0 plus Misskey-specific additions. The core specification is identical, so basic federation works. The differences appear in the additional properties attached to activities. For example, Mastodon adds a sensitive property to indicate NSFW content. Sharkey uses a cw property for content warnings. Both servers may interpret the other’s property incorrectly, leading to content warnings not appearing as expected.
Features That Do Not Transfer Between Mastodon and Sharkey
Several features that work within Sharkey do not display correctly on Mastodon. Knowing these limitations helps avoid frustration.
- Custom emoji reactions
Sharkey allows users to react to posts with any custom emoji from their instance. Mastodon only supports favoriting. When a Sharkey user reacts with a custom emoji, Mastodon displays it as a favorite or ignores it. The Mastodon user never sees the specific emoji. To work around this, Sharkey users can use the star or heart reaction, which Mastodon treats as a favorite. - Quote posts
Sharkey supports quote posts, which combine a reshare with a comment. Mastodon does not support quote posts natively. When a Sharkey user quotes a Mastodon post, Mastodon users see the quote as a separate post with a link to the original. The Mastodon user cannot see the quote structure or the original post embedded within it. - Polls with multiple choices
Mastodon supports single-choice polls only. Sharkey supports multiple-choice polls. When a Sharkey user creates a multiple-choice poll, Mastodon users see the poll but can only select one option. The Mastodon server may also display the poll incorrectly, showing all options as checkboxes instead of radio buttons. - Visibility settings
Sharkey offers more granular visibility settings than Mastodon, including followers-only, home-only, and specified users. Mastodon supports public, unlisted, followers-only, and direct. When a Sharkey user posts with a visibility setting that Mastodon does not recognize, Mastodon treats it as followers-only. This can cause posts meant to be public to appear only to followers on Mastodon. - Media descriptions and alt text
Both platforms support alt text for images. However, Sharkey allows longer descriptions than Mastodon. Mastodon truncates descriptions that exceed its limit of 1,500 characters. Users should keep alt text under 1,500 characters to ensure it displays fully on Mastodon.
Common Federation Problems and Workarounds
Missing notifications for reactions on Mastodon
When a Sharkey user reacts to a Mastodon post with a custom emoji, the Mastodon user does not receive a notification. The Mastodon server may not even store the reaction in the database. To receive a notification, the Sharkey user should use the favorite button instead of a custom emoji. Mastodon treats all favorites as notifications.
Content warnings not displaying on Sharkey posts viewed from Mastodon
Sharkey uses a cw property for content warnings, while Mastodon uses sensitive. When a Sharkey user adds a content warning, Mastodon may not display it if the Sharkey instance does not also set the sensitive flag. To ensure content warnings display on Mastodon, Sharkey users should enable the NSFW flag on their posts in addition to the content warning text.
Sharkey posts appearing as unlisted on Mastodon
If a Sharkey user posts with the visibility set to “home” or “followers” only, Mastodon treats it as followers-only. If the Sharkey user intends a post to be public but uses a custom visibility setting, Mastodon may hide it from the public timeline. Always use the “public” visibility setting on Sharkey for posts that should appear in Mastodon’s public timelines.
Mastodon vs Sharkey: Feature Support Comparison
| Feature | Mastodon | Sharkey |
|---|---|---|
| Custom emoji reactions | Not supported | Supported |
| Quote posts | Not supported | Supported |
| Multiple-choice polls | Not supported | Supported |
| Granular visibility settings | Limited to 4 levels | Extended visibility options |
| Content warning display | Uses sensitive flag | Uses cw property |
| Basic follows and boosts | Fully compatible | Fully compatible |
Mastodon and Sharkey can federate successfully for basic operations. Users should adjust their expectations for advanced features. Sharkey users who want full interaction with Mastodon should avoid custom emoji reactions and quote posts. Mastodon users should understand that Sharkey posts may include features they cannot see. Both platforms continue to evolve, and future updates may improve compatibility.