AntiFirmament
by axlecoffee
AntiFirmament blocks a packet that the Firmament mod sends to servers when players join, so mod IDs are not reported without consent.
What it does
Firmament attempts send a packet to servers on join that lists the mods a player has installed, and Hypixel is one server where these mod IDs are displayed. Fabric itself does not send this data. AntiFirmament intercepts the ModAnnouncer packet that Firmament sends, so the server does not receive the list. Only the client needs the mod, and servers run without it.
The mod is open source under the MIT License and is published for Fabric only. Its latest file is 1.0.3 for 26.3, dated 2026-10-13, and the builds cover 1.21.10 – 26.3 across seven release versions. Its author describes it as a response to a mod whose announcer was built personally and not widely shared. Players who want to keep their mod list private on servers can use it to stop the packet from leaving the client.
Key features
Blocks the mod announcer packet
The packet that Firmament sends when a player joins a server is blocked before it reaches the server.
Keeps the mod list private
Mod IDs in the mod folder are not sent to servers without the player's knowledge or consent.
Does not change normal Fabric behavior
Fabric's usual handshake is left alone, so only the Firmament announcement is affected.
Compatibility
Latest build for each game version and loader.
Only full game releases are shown. This mod publishes no snapshot builds.
Use cases
Private modpacks on public servers
A player who joins servers with a custom modpack can keep the list of installed mods from being shown to the server owner.
Tracking Firmament's behavior
Players who want to see how a server reacts without the announcement can join with this mod installed.
Who it’s for: Players who use Fabric on Minecraft 1.21.10 or later and do not want Firmament's packet sent to servers they join. Server owners need take no action, because the mod runs only on the client.
How it compares
Firmament Mod Announce Remover is the closest alternative: it is also client-side only, is published for Fabric across 1.21.5 – 1.21.11, and is released under CC0 1.0 Universal, which is open source. Skyblock Itemtracker is client-side only for Fabric and covers 1.21.11 – 26.1, under the MIT License. Arbitrary Effect Killer is a Fabric mod for 1.21.10 – 1.21.11 that runs on the server only, so players join without installing anything, and it uses the MIT License.
| Mod | Loaders | Game versions | Environment | Updated |
|---|---|---|---|---|
| AntiFirmament | Fabric | 1.21.10 – 26.3 | Client-side only | 2026-10-13 |
| Firmament Mod Announce Remover | Fabric | 1.21.5 – 1.21.11 | Client-side only | 2026-03-20 |
| Skyblock Itemtracker | Fabric | 1.21.11 – 26.1 | Client-side only | 2026-04-01 |
| Arbitrary Effect Killer | Fabric | 1.21.10 – 1.21.11 | Server-side only | 2026-03-21 |
Questions
Does AntiFirmament need a Fabric API install?
Does the server need AntiFirmament installed?
Which game versions does AntiFirmament support?
In the catalog
AntiFirmament is one of 3,545 Optimization mods on ModsFinder, and one of 2,575 Optimization mods for Fabric. 8,071 mods support Minecraft 26.3.
More from axlecoffee
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What the author says
This mod attempts to block the ModAnnouncer packet the mod Firmament attempts to send while joining servers. This is NOT normal Fabric behavior - as only Forge has a mod announcer built in, and personally I don't see a need for one to exist in Fabric. No server is required to see my mod's folder (MOD IDs) and no…
Official listing
- Modrinth page
- modrinth.com/mod/antifirmament
- Owner
- axlecoffee
- Published
- 2026-02-02
- Updated on Modrinth
- 2026-10-13
- Facts verified
- 2026-10-15