Modpack testing and optimization · Minecraft Java Edition

Stop guessing which mod
broke your server.

ModTamer creates a copy of your server, boots it in an isolated sandbox, bisects the mods breaking it, installs the dependencies it needs, and verifies the fix by booting again. Your original server is never modified while it works — only when you decide to apply the fix.

Analyse a crash log — free Get notified at launch

Forge & NeoForge Runs on your machine No account to try it

ModTamer analysing a 59 mod Forge 1.20.1 pack: 12 required dependencies and 28 findings, with the list of mods and the reason for each finding.
A real 59-mod Forge pack. 12 required dependencies, 28 findings, each with its reason.

What it does

Reading a log tells you what already broke.
ModTamer finds out why.

01

Diagnose

Reads every jar, builds the dependency graph and lists what is wrong — with the reason for each finding. No size limit, and it never launches anything.

02

Isolate

Boots your pack repeatedly in a sandbox, halving the mod list each time, until it has the smallest set that still reproduces the crash.

03

Repair

Resolves the dependencies that can be obtained from metadata, and tells you plainly which problems still need a human. It never guesses a mod by searching for its name.

04

Benchmark

Measures TPS, tick time and per-mod cost under a documented load, so "it lags" turns into a number you can act on.

05

Validate

Talks to the running server's console and asks whether each mod actually registered its content — catching the ones that load and then silently do nothing.

06

Update

Tests newer versions in a copy and boots them before you apply anything to the server people are playing on.

07

Migrate

Tells you exactly what you would lose moving to a new Minecraft version, before you spend a weekend finding out.

The part nobody else does

It does not read the log.
It reproduces the crash.

When the log is not enough, ModTamer boots your pack over and over in a sandbox, halving the mod list each time, until only the culprit is left. Below: a real run, start to finish.

ModTamer isolating a broken pack: it confirms the failure, narrows down across four test boots, and reports the mod with the missing dependency in one minute and twenty-seven seconds.
Four test boots. One minute twenty-seven. One missing dependency, found.

How it works

Three steps. The work happens on a copy.

  1. 1

    Point it at your server folder

    Drag it onto the window. ModTamer reads every jar, builds the dependency graph and lists what is wrong — in seconds, without launching anything.

  2. 2

    It works on a copy

    Every experiment runs on an isolated snapshot with its own Java and its own world. Your original folder is never modified. That is not a setting; it is how it is built.

  3. 3

    You decide what gets applied

    Nothing reaches your real server unless you say so. When it does, a backup is taken first, and only jars inside mods/ are written — never your world or your configuration.

Free, right now

Paste a crash log.

No account, no install. It tells you what failed and which mods are involved.

Analysed in memory and discarded. Paths containing your username are stripped before anything is shown back. By using it you accept the terms and the privacy policy.

Plans

Not on sale yet.

Checkout opens once our payment provider has reviewed this site. Leave your email to hear when it does.

Free

$0

No card, ever

  • Static analysis of any pack — no size limit, ever
  • The dependency graph and every finding
  • One complete test run, whatever size your pack is
  • The log analyser on this page — no account, ever
Available at launch

Standard

US$7.99

per month

  • Everything in Free
  • Unlimited isolation, repair and validation runs
  • Boots packs up to 200 mods
  • Two computers
  • Performance benchmarking
Locked

Pro

US$17.99

per month

  • Everything in Standard
  • No artificial mod limit — your hardware is the limit
  • Five computers
  • Version migration planning
  • Live server monitoring
Locked

The log analyser on this page never asks for an account. Free does, because one run per person has to be counted somewhere.

Analysis is never capped, on any plan. Your first complete test run is free whatever the size of your pack. What a plan buys is doing it again, as often as you need.

Never "unlimited mods": in Pro the ceiling is set by Minecraft, the loader and your hardware, not by ModTamer. Prices are in US dollars; taxes are calculated at checkout by Paddle, our authorised reseller and Merchant of Record, who will be the seller for your purchase.

Verified

What we actually test.

These are the combinations ModTamer boots and checks automatically. Outside them it may work, but nothing has verified it, so we make no claim.

  • forge · Minecraft 1.20.1
  • neoforge · Minecraft 1.21.1

Launch

Tell me when it ships.

Only one message when it launches. That's the whole plan.