Lag Detective
by Mouldytoast
Lag Detective is a Fabric diagnostics mod that helps answer where server lag is coming from, using TPS and MSPT readings and entity chunk activity.
What it does
The mod monitors server ticks per second (TPS) and milliseconds per tick (MSPT), and tracks entity activity by chunk, so an operator can see which part of the world is taking time. Lag is sorted into clear classes in the output, and the results are shown through simple commands that print readable reports.
Its diagnostics run on the server side, and the mod can generate a complete diagnostic report that a player or server owner can attach when asking for debugging support. An optional client dashboard can display the same monitoring data in real time.
Lag Detective is released under the MIT License and is not open source. Files are published for Fabric only, for 1.21.11.
Key features
TPS and MSPT monitoring
Tick rate and per-tick processing time are measured continuously, showing how long the server spends on each tick.
Entity chunk tracking
Entity activity is recorded per chunk, so heavy areas of the world can be located without guessing.
Lag classification
Detected lag is grouped into categories, so the source of a slowdown is easier to read in the report.
Optional client dashboard
A dashboard on the client can show live performance figures alongside the server's own diagnostics.
Compatibility
Latest build for each game version and loader.
Only full game releases are shown. This mod publishes no snapshot builds.
Use cases
Diagnosing a slow server
An operator who notices stutter can run the diagnostic commands to find whether entities, chunks or ticks are responsible.
Requesting support
A full diagnostic report gathers the measurements into one file that can be sent to others when asking for help.
Who it’s for: Server owners and administrators who need to find the cause of lag on a Fabric server. Players who run a local server for friends can use it in the same way.
How it compares
LagLens is a client-side only Fabric mod under the MIT License, for 1.21.1, so it covers the client rather than the server. TickShield is a server-side only mod under the Mozilla Public License 2.0 and is open source, for 1.21.11, the same version as Lag Detective. TPSChecker is server-side only under the MIT License, but it is built for 1.21.5 alone.
| Mod | Loaders | Game versions | Environment | Updated |
|---|---|---|---|---|
| Lag Detective | Fabric | 1.21.11 | Client or server, optional | 2026-02-02 |
| LagLens | Fabric | 1.21.1 | Client-side only | 2026-06-13 |
| TickShield | Fabric | 1.21.11 | Server-side only | 2026-04-12 |
| TPSChecker | Fabric | 1.21.5 | Server-side only | 2025-06-23 |
Questions
Does Lag Detective need to be installed on the server?
Which loader does Lag Detective use?
Can the diagnostic report be shared?
In the catalog
Lag Detective is one of 3,545 Optimization mods on ModsFinder, and one of 2,575 Optimization mods for Fabric. 19,862 mods support Minecraft 1.21.11.
More from Mouldytoast
Similar mods
What the author says
It provides real-time performance monitoring, clear lag classification, and easy-to-read reports through simple commands and an optional client dashboard.
Official listing
- Modrinth page
- modrinth.com/mod/lagdetective
- Owner
- Mouldytoast
- Published
- 2026-02-02
- Updated on Modrinth
- 2026-02-02
- Facts verified
- 2026-10-15