What Is MegaMekLab and How Do You Use It to Build BattleTech Units?
MegaMekLab is the unit design and editing tool in the MegaMek suite: a Java application for building and modifying Classic BattleTech units such as 'Mechs, vehicles, and infantry, with validation against construction rules and export into formats that MegaMek and MekHQ can load. Use it when you want to create a custom unit, check whether an existing design is legal, or prepare units for play or a campaign. It is part of the same open-source, GPL-licensed project as MegaMek and MekHQ.
Where MegaMekLab fits in the suite
The three tools split the work of a tabletop session:
| Tool | Role | What you do in it |
|---|---|---|
| MegaMek | Gameplay | Play out battles on maps with the units you've built or selected |
| MekHQ | Campaign management | Track a persistent force, pilots, repairs, and contracts over time |
| MegaMekLab | Unit design and editing | Build, edit, and validate individual units |
MegaMekLab is the starting point when the unit you want doesn't exist yet or needs a rules check. Once a design is saved, it becomes an input to the other two: MegaMek for a one-off game, MekHQ for a campaign roster.
Building a unit
The workflow is the same whether you start from scratch or open an existing file.
- Choose a unit type and starting point. Select the category you want to build ('Mech, vehicle, infantry, and so on), or open an existing unit file to edit it. Starting from a close existing design is usually faster than building from an empty chassis.
- Set the base characteristics. For a 'Mech this means tonnage, internal structure, engine rating and type, heat sinks, armor, and movement profile. These choices cascade: tonnage and engine determine how much space and mass remain for everything else.
- Add equipment. Place weapons, ammunition, and other gear into the available critical slots and mass budget. The interface tracks remaining tonnage and slots as you go, so you can see when a design no longer fits.
- Watch the validation feedback. MegaMekLab checks the design against Classic BattleTech construction rules and flags problems rather than silently allowing them. Treat any warning as something to resolve before you rely on the unit.
- Save the unit. Save it in the format the suite uses so MegaMek and MekHQ can read it.
Common sticking points
- Overweight or overslotted designs. If the tonnage or critical space runs out, the fix is usually to reduce armor, drop a weapon, or change the engine — not to force the design through.
- Tech base and era mismatches. Equipment availability depends on the tech base and era you've selected. A component that seems missing is often just outside the current setting.
- Validation warnings you don't understand. Read the specific rule the warning names; it usually points at the exact field that needs to change.
Getting units into MegaMek and MekHQ
Because all three tools share the same unit file format, the handoff is a file operation rather than a conversion:
- Into MegaMek: place or select the saved unit so it appears in your available forces for a game.
- Into MekHQ: add the unit to your campaign force so it can be assigned, repaired, and tracked like any other unit in the roster.
If a unit doesn't show up, the usual cause is that it was saved somewhere the other tool isn't looking, or it failed validation and wasn't written out cleanly.
When to use it — and when not to
Reach for MegaMekLab when you need a new or modified unit or a rules check on a design. You don't need it to simply play a battle with existing units (that's MegaMek) or to run a campaign (that's MekHQ). For a quick game with stock units, skip straight to MegaMek; for a long-running force, build or verify your units in MegaMekLab first, then bring them into MekHQ.