TslatEffectsLib
by Tslat
TslatEffectsLib is a library that extends Minecraft's MobEffect class with hooks for instance-sensitive behavior and application callbacks.
What it does
The vanilla MobEffect class exposes only a limited set of basic functions. The library adds hooks to it, so a mod can make a status effect react to its own instance: its tick behavior, display name and shouldTick check can all depend on the specific effect, and it can run callbacks when the effect is applied, reapplied or removed.
Mod authors can also use built-in checks for whether an effect can apply to a target and whether it is mutually exclusive with another effect. These cover cases that would otherwise need extra events or mixins to combine. The library is required by R.E.P.O. Love Potion, and the author notes that its documentation covers most of what a developer needs.
Client and server both need the library, since it changes effect behavior on the game logic side. Files are published for Fabric, Forge and NeoForge across 15 release versions, 1.19 – 1.21.5, and the code is open source under the MIT License.
Key features
Instance-sensitive ticking
The tick method and shouldTick check can be decided per effect instance rather than once for the whole effect type.
Instance-sensitive display name
An effect can show a different name depending on its instance, which lets one status effect vary its label.
Application checks
Checks decide whether an effect can be applied to a target and whether it excludes another effect.
Lifecycle callbacks
Callbacks run when an effect is first applied, reapplied or removed, so mods can react at each stage.
Compatibility
Latest build for each game version and loader.
1.21.x4 of 4 versions with builds
1.20.x6 of 6 versions with builds
1.19.x5 of 5 versions with builds
Only full game releases are shown. This mod publishes no snapshot builds.
Required by 1 mod
Use cases
Custom effect mechanics
A mod author can build effects whose strength, timing or appearance changes with the instance, without writing separate events or mixins.
Who it’s for: Mod developers who add status effects to Minecraft. Players do not interact with the library directly, but it must be installed for dependent mods to load.
How it compares
Tweak API is a Fabric library under the Apache License 2.0, with files for 1.20.1 – 1.21.8, and it can run on either the client or the server. Equipment Benediction is a Forge mod under the MIT License, covering 1.19.2 – 1.20.6, which requires both the client and server. A Mimir is a Fabric server-side only mod under the CC0 1.0 Universal license, targeting 1.21.11, and it is not open source. TslatEffectsLib is a client and server library, so both sides need it.
| Mod | Loaders | Game versions | Environment | Updated |
|---|---|---|---|---|
| TslatEffectsLib | Fabric, Forge and NeoForge | 1.19 – 1.21.5 | Client and server | 2025-09-17 |
| Equipment Benediction | Forge | 1.19.2 – 1.20.6 | Client and server | 2024-06-30 |
| A Mimir | Fabric | 1.21.11 | Server-side only | 2026-01-25 |
Questions
Does R.E.P.O. Love Potion need TslatEffectsLib?
Do players need to install TslatEffectsLib on both sides?
Which loaders have TslatEffectsLib files?
In the catalog
TslatEffectsLib is one of 3,514 Library mods on ModsFinder, and one of 2,348 Library mods for Fabric. 15,307 mods support Minecraft 1.21.5.
More from Tslat
Similar mods
What the author says
A small library for making MobEffects easier to use, and more dynamic The existing MobEffect class in Minecraft is very limited and has only very specific and basic functionality.
Official listing
- Modrinth page
- modrinth.com/mod/tslateffectslib
- Owner
- Tslat
- Published
- 2022-12-17
- Updated on Modrinth
- 2025-09-17
- Facts verified
- 2026-10-15