You’ve finally done it. You’ve beaten the Act 3 boss with the Ironclad, the Silent, and the Defect. You’re feeling like a god, watching the credits roll, and then you notice those three empty slots glowing on the top left of your screen in the next run. You know you need them. You know there’s a "true" ending out there. But every time you reach a campfire, you’re staring at that slay the spire ruby key and wondering: is it actually worth giving up a card upgrade right now?
Honestly, the Ruby Key is the weirdest of the bunch. The Emerald Key makes you fight a super-buffed elite, and the Sapphire Key asks you to skip a potentially run-winning relic. But the Ruby Key? It just asks for your time. Specifically, it asks for a campfire slot. It feels free, but in a game where one upgraded Whirlwind or Noxious Fumes determines if you live or die, "free" is a dangerous word.
How to Actually Get the Ruby Key
Getting your hands on the slay the spire ruby key is technically the easiest part of the Act 4 quest. You don’t have to hunt down a burning icon on the map or sacrifice a rare relic. You just go to a Rest Site (a campfire) and look at your options.
Alongside the usual "Rest" to heal or "Smith" to upgrade a card, you’ll see a new option: Recall.
Clicking Recall immediately grants you the Ruby Key. That’s it. No fight, no gold cost, no RNG. But there is a catch—you can't do anything else at that campfire. If you're at 5 HP and desperately need to rest, or if you have a Limit Break that needs to be upgraded to lose its "Exhaust" tag, taking the key might actually end your run before you even see the Heart.
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Why Does It Only Show Up Sometimes?
If you’re playing and don’t see the option to Recall, don’t panic. You probably haven’t "unlocked" the keys for your current save file yet. To make the keys appear in your runs, you must:
- Complete a standard run (beat the Act 3 boss) with the Ironclad.
- Do the same with the Silent.
- Do it one more time with the Defect.
Once those three are checked off, the Ruby, Emerald, and Sapphire keys will appear in every single run going forward, regardless of which character you play (yes, even the Watcher).
The Biggest Mistake Players Make With the Ruby Key
Most players—myself included for a long time—grab the slay the spire ruby key way too early. You see a campfire in Act 1, you’re at full health, and you think, "I'll just get this out of the way now."
Don't do that.
Act 1 is when your deck is at its weakest. Every single card upgrade in Act 1 is worth its weight in gold. Upgrading your main damage card can be the difference between taking 0 damage from a Gremlin Nob or taking 35 and limping through the rest of the floor.
The Ruby Key is always available at every single campfire until you take it. It doesn't "run away."
Expert Tip: The best time to take the Ruby Key is almost always the very last campfire in Act 3, right before the final boss.
By that point, your deck is usually "solved." One extra upgrade on a Defend isn't going to change your fate against the Corrupt Heart, but it definitely might change your fate against the Act 1 Sentries.
Comparing the Three Keys
You can't just get the Ruby Key and call it a day. If you want to see Act 4, you need the whole set. It's basically a scavenger hunt that actively tries to kill you.
- Ruby Key (The Sacrifice): Obtained at a campfire. Costs you one upgrade or one heal.
- Emerald Key (The Skill Test): Obtained by defeating a "Burning Elite." These are the elite icons on the map that have a flickering flame effect. They have extra HP, Strength, or Metallicize.
- Sapphire Key (The Opportunity Cost): Obtained in a non-boss treasure chest. You have to choose the key instead of the relic inside.
If you forget even one of these, the run ends after the Act 3 boss. You’ll get the "Victory?" screen, your character will flop over, and you’ll be left wondering why you didn't just take the blue key when you had the chance.
Strategy: When to Pivot for the Key
Slay the Spire is a game of momentum. Taking the slay the spire ruby key is a momentum killer.
If you find yourself with the Fusion Hammer boss relic (which prevents you from Smithing anyway), the Ruby Key becomes "free." In that specific case, grab it whenever you don't need to heal. If you have the Coffee Dripper (no resting), you’re going to be Smithing anyway, so the decision becomes a bit tighter.
Think about your pathing. If you see a path in Act 3 with four campfires, you can easily afford to spend one on the Ruby Key. If you’re taking a high-risk path with lots of Elites and only one campfire, you might have to skip the Heart run entirely if your HP is too low.
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Is the Ruby Key Required for Ascension?
This is a common point of confusion. You do not need any keys to increase your Ascension level.
If you are just trying to climb from Ascension 5 to Ascension 6, you can completely ignore the slay the spire ruby key. Just beat the Act 3 boss, and the next level will unlock. People usually only go for the keys if they want the satisfaction of beating the Heart or if they are playing at Ascension 20 and want the "Full Clear" experience.
Honestly, the Heart is a completely different beast. It requires a specific kind of deck—usually one that can generate massive block every turn or deal hundreds of damage very quickly. If your deck feels "just okay," don't bother with the keys. Just take the win at Act 3 and move on.
Summary of Actionable Steps
If you're ready to stop dying at the end of Act 3 and actually use that slay the spire ruby key to reach the endgame, follow this checklist:
- Wait until Act 3: Unless you have Fusion Hammer or literally every card in your deck is already upgraded, do not Recall in Act 1 or 2.
- Assess your HP: Before clicking Recall, look at the upcoming boss. If it's Time Eater and you're at 20% HP, Rest. You can find another campfire later.
- Check your inventory: Always double-check your top-left UI before the final Act 3 boss. It is a soul-crushing feeling to beat Awakened One and realize you’re missing the Ruby Key because you forgot to click Recall at the last stop.
- Prioritize the Emerald Key first: Usually, the Burning Elite is the hardest part. Secure that in Act 1 or 2 if your deck is strong, then the Ruby Key becomes a simple "tax" you pay at the end of the run.
Next time you’re sitting at that campfire, don’t just mindlessly upgrade a Strike. Look at your keys. Plan the sacrifice. The Heart is waiting.