Lag Spike Profiler
by Meldexun
Lag Spike Profiler is a Forge profiler for Minecraft 1.12.2 that records per-frame client thread data to find what causes frame time spikes.
What it does
A recording starts with a command that sets how many seconds to profile. When the duration ends, the result is saved to the Minecraft instance folder under a file named after the current time, using the format yyyy-MM-dd HH-mm-ss with the .lagspikeprofile extension. A saved file can then be opened with the separate LagSpikeProfiler Viewer.
The mod targets the client thread specifically, so the data reflects work done for each rendered frame. That makes it possible to see which part of the frame accounts for a lag spike rather than only knowing that one occurred. Lag Spike Profiler runs on Forge for 1.12.2 only, and it requires MixinBootstrap to be installed alongside it. Servers do not need it; each player installs it for their own game.
Files are published for Forge 1.12.2 only, with 1.12.2-1.1.4 as the latest file, released 2026-07-02. The first release dates from 2026-01-01. The code is under All rights reserved and is not open source, though its source code and issue tracker are publicly linked.
Key features
Per-frame profiling
Records accurate timing for each frame of the client thread, so spikes can be traced to their cause.
Timed profile runs
A command starts a profile that lasts for a chosen number of seconds and then stops on its own.
Timestamped result files
Each result is written to the instance folder with a name built from the date and time it finished.
Separate result viewer
Saved profiles are opened in LagSpikeProfiler Viewer, a companion tool that reads the .lagspikeprofile files.
Compatibility
Latest build for each game version and loader.
Only full game releases are shown. This mod publishes no snapshot builds.
Requirements
Dependencies declared by the latest file for each loader.
Required 1
Use cases
Who it’s for: The mod suits players and modpack authors on Forge 1.12.2 who want to investigate client-side frame time problems. It does not inspect the server, so server tick lag is outside its scope.
How it compares
Spark Unforged is a Forge mod for 1.12.2 that is open source under the GNU General Public License v3.0 only, and it is optional on the client or server, so either side can run it and neither needs it. More Profiling covers Fabric, Forge and Quilt for 1.20 – 1.21.3, is open source under the MIT License, and is also optional on either side. Lag Spike Profiler, by contrast, is client-side only, so only the client needs it and servers run without it.
| Mod | Loaders | Game versions | Environment | Updated |
|---|---|---|---|---|
| Lag Spike Profiler | Forge | 1.12.2 | Client-side only | 2026-07-02 |
| Spark Unforged | Forge | 1.12.2 | Client or server, optional | 2025-07-10 |
| More Profiling | Fabric, Forge and Quilt | 1.20 – 1.21.3 | Client or server, optional | 2024-11-07 |
Questions
Does Lag Spike Profiler need MixinBootstrap?
Does a server need Lag Spike Profiler?
Where are profile results stored?
In the catalog
Lag Spike Profiler is one of 3,545 Optimization mods on ModsFinder, and one of 1,441 Optimization mods for Forge. 2,920 mods support Minecraft 1.12.2.
More from Meldexun
Similar mods
What the author says
Profile the client thread to get per frame data to indentify the cause of frame time lag spikes.
Official listing
- Modrinth page
- modrinth.com/mod/lag-spike-profiler
- Owner
- Meldexun
- Published
- 2026-01-01
- Updated on Modrinth
- 2026-07-02
- Facts verified
- 2026-10-15