Effect: +10% chance to open chests for free. If a chest opens for free, the price of the next chest does not increase.
Unlock: Purchase items from 25 chests
The Key is a Common item that gives each chest you open a chance to be free. When it triggers, you get the item inside without paying gold and - critically - the chest price does not increase afterward. This means a free chest is a pure gain: you get an item and your gold counter is unaffected.
There is one important mechanical detail: the free chest roll happens after you receive the item from the chest, not before. This means if a chest contains a Key, you can trigger the free chest proc on that same chest that gave you the Key. Finding a Key mid-run immediately applies to the current chest.
Luck does not affect the Key's proc chance. The free chest roll is independent of your Luck stat entirely.
The Key is one of the most consistently valuable items in the game despite being Common rarity. More free chests means more items per run, which compounds over time. The earlier you find it the more value it generates, but it is worth taking at any point in a run.
Its value scales with how many chests you open in a run. Builds that actively seek out chests - using the AFK Challenge strategy or gold-generating builds with Robinette - get more mileage from the Key than builds that only open the occasional chest. The first Key is the most impactful due to diminishing returns on stacking.
Multiple Keys do not add their chances linearly. The game uses a diminishing returns formula based on the total key chance:
In practice this means the first Key adds 9.1% free chest chance. The second adds 7.6% more. By 10 Keys you are at exactly 50%. The returns shrink with each copy but never reach zero - you can always stack more Keys for a marginal benefit.
| Keys | Free Chest Chance | Increase per Key | Expected Chests Per Free |
|---|---|---|---|
| 1 | 9.10% | - | 11 |
| 2 | 16.70% | +7.60% | 6 |
| 3 | 23.10% | +6.40% | 4.3 |
| 4 | 28.60% | +5.50% | 3.5 |
| 5 | 33.30% | +4.80% | 3 |
| 6 | 37.50% | +4.20% | 2.7 |
| 7 | 41.20% | +3.70% | 2.4 |
| 8 | 44.40% | +3.30% | 2.2 |
| 9 | 47.40% | +2.90% | 2.1 |
| 10 | 50.00% | +2.60% | 2 |
The stacking table above is sourced directly from the megabonk.wiki, which notes the values were verified via datamining and in-game testing. The in-game item description says "+10%" but the actual proc rate on a single Key is 9.1% due to the formula. Both sources confirm this discrepancy.
| Property | Details |
|---|---|
| Unlock condition | Purchase items from 25 chests |
| Purchase | After unlocking, buy with Silver from Main Menu - Unlocks - Items |
| Rarity | Common |
| Luck interaction | Luck does not affect the free chest proc chance |
The 25 chest purchases count across all runs and all characters. Any paid chest opened contributes to the total. This is one of the more passive unlock conditions in the game - you will naturally hit it by playing normally, without needing to prioritize chests specifically for the unlock.
Fox - Fox's passive improves Luck, which improves the rarity of items found in chests. Key doesn't interact with Luck directly, but Fox opening more chests for free means more rolls at high-rarity loot from Fox's Luck passive. The combination gets more Legendary and Epic items per run than most other setups.
Robinette - Robinette's damage scales with gold held. Free chests preserve gold, which keeps Robinette's gold pool higher for longer. Combined with the Golden Shield + Kevin gold-generation combo noted in the wiki, Key can significantly increase total items collected before the third stage boss.
The Key gives each chest you open a chance to be free. The actual proc chance on a single Key is 9.1% (the formula gives slightly less than the stated +10%). If a chest opens for free, the chest price does not increase. The free chest roll happens after you collect the item, so a chest that gives you a Key can itself proc as free.
Purchase items from 25 chests across any number of runs. This counts cumulatively - you do not need to open 25 chests in a single run. After meeting the condition, buy the Key from Main Menu - Unlocks - Items with Silver.
No. Luck does not affect the Key's free chest proc chance. The wiki confirms this explicitly. Luck improves the rarity of items found inside chests but has no effect on whether the chest itself opens for free.
Multiple Keys use a diminishing returns formula: freeChestChance = totalKeyChance / (totalKeyChance + 1). One Key gives 9.1% free chest chance. Five Keys give 33.3%. Ten Keys give exactly 50%. Each additional Key still adds value, but the improvement gets smaller with each copy.
The Key scales with the number of chests you open in a run. It does not scale with player level, Damage, or any combat stat. The more chests you find and open, the more total value you extract from each Key. Builds that generate gold or reduce chest costs get the most out of stacking Keys.
