mcMMO Unofficial Docs

How mcMMO's Smelting child skill works. Second Smelt for double output, Fuel Efficiency for longer-burning fuel, and the vanilla XP boost, plus how Smelting's level comes from Mining and Repair.

Smelting is the furnace skill. Cook ores and items in a furnace and Smelting quietly works in the background: a chance to double your output (Second Smelt), longer-lasting fuel (Fuel Efficiency), and a boost to the vanilla XP you get from smelting.

Smelting is a child skill: it earns no XP of its own. You can't level Smelting directly. Its level is the average of your Mining and Repair levels, rounded down. To raise Smelting, level up those two parent skills.


Type	Child skill
Parent skills	Mining + Repair
How its level is set	`(Mining level + Repair level) ÷ 2`, rounded down
Super ability	None
Sub-skills	Second Smelt, Fuel Efficiency, Understanding the Art (vanilla XP boost)
Command	`/smelting`

How your Smelting level is calculated

Smelting is a child skill, so mcMMO never grants it XP. Instead it computes your Smelting level on demand:

Smelting level = floor( (min(Mining, MiningCap) + min(Repair, RepairCap)) ÷ 2 )

Each parent is clamped to its own level cap, then the two are averaged. If you're Mining 90 and Repair 30, your Smelting level is (90 + 30) ÷ 2 = 60. The best way to climb Smelting is to push both Mining and Repair up. Relying on just one parent caps your average at half its level.

Second Smelt: double your output

Second Smelt is the main payoff. Whenever a furnace finishes smelting an item, you have a chance to get one extra copy of the result for free.

Mode	Maxes out at level	Maximum chance
Standard	100	50%
RetroMode	1000	50%

The chance ramps linearly from 0% up to 50% at the cap, so a maxed-out Smelter doubles roughly half of everything they smelt.

Smelting:
    SecondSmelt:
        ChanceMax: 50.0
        MaxBonusLevel:
            Standard: 100
            RetroMode: 1000

Second Smelt only triggers when the furnace's output slot has room (it won't push a stack past its limit), and only for items the server allows double drops on.

Fuel Efficiency: fuel that lasts longer

Fuel Efficiency multiplies the burn time of every piece of fuel you put in a furnace, so each coal/lava bucket/etc. smelts more items.

Rank	Standard level	RetroMode level	Burn-time multiplier
1	10	100	×2
2	50	500	×3
3	75	750	×4

At rank 3 your fuel burns four times as long: a single piece of coal smelts 32 items instead of 8. (The boosted burn time is clamped to a sane maximum internally so it never overflows.)

Understanding the Art: vanilla XP boost

"Understanding the Art" is the sub-skill behind Smelting's vanilla experience boost: the green XP orbs a furnace gives you when you collect smelted items are multiplied based on its rank.

Rank	Standard level	RetroMode level	Vanilla XP multiplier
1	10	100	×1
2	25	250	×2
3	35	350	×3
4	50	500	×3
5	65	650	×4
6	75	750	×4
7	85	850	×5
8	100	1000	×5

At rank 8 you earn five times the normal vanilla XP from smelting.

Smelting:
    VanillaXPMultiplier:
        Rank_1: 1
        # ... up to Rank_8: 5

Flux Mining: currently inactive

The official wiki and mcMMO's config files still list Flux Mining, a sub-skill that would instantly smelt ores as you mine them, with a 33% chance. Its config block and permission node (mcmmo.ability.smelting.fluxmining) both exist.

Flux Mining does not function in mcMMO 2.2.054. The code that would run it is commented out in the block-break listener, and the in-game /smelting display for it is disabled. Even though advanced.yml still has a FluxMining section (33% chance) and the permission node is defined, the feature has no effect. Treat it as non-functional until a future version re-enables it.

# Present in advanced.yml but the code path is disabled in 2.2.054
Smelting:
    FluxMining:
        Chance: 33.0
        MaxBonusLevel:
            Standard: 100
            RetroMode: 1000

Commands & permissions

Node	What it grants
`mcmmo.skills.smelting`	Use the Smelting skill at all
`mcmmo.commands.smelting`	Use the `/smelting` command
`mcmmo.ability.smelting.secondsmelt`	Second Smelt
`mcmmo.ability.smelting.fuelefficiency`	Fuel Efficiency
`mcmmo.ability.smelting.vanillaxpboost`	Vanilla XP boost (Understanding the Art)
`mcmmo.ability.smelting.fluxmining`	Flux Mining (defined but non-functional in 2.2.054)
`mcmmo.ability.smelting.all`	Every Smelting sub-skill
`mcmmo.perks.lucky.smelting`	"Lucky" perk: ~33.3% better activation odds

See Permissions for the full list and how to assign them.

Quick reference

Sub-skill	Trigger	Max effect	Notes
(Skill level)	—	avg(Mining, Repair)	No direct XP; level the parents
Second Smelt	Furnace finishes smelting	50% at level 100	One extra output item
Fuel Efficiency	Smelting with fuel	×4 burn time at rank 3	Rank 3 = Smelting 75
Understanding the Art	Collecting furnace XP	×5 vanilla XP at rank 8	Rank 8 = Smelting 100
Flux Mining	—	none	Non-functional in 2.2.054

Smelting