Spiral Knights is a Massively Multiplayer Online (MMO) dungeon crawler strongly influenced by Zelda and Phantasy Star Online. You play as a Spiral Knight, making your way down through The Clockworks towards the center of the planet in an effort to restore power to your encampment's crash-landed spaceship. Each floor of the Clockworks is randomly-generated and involves switch-activation, traps and combat. While the common areas allow for large numbers of active players, the dungeons are instanced for only 1-4 players.
Spiral Knights is a free-to-play MMO. It limits your play each day via the resource called 'energy.' You are provided 100 units of energy each day, and it costs 10 energy to descend to each floor of a dungeon. If you die in combat, you can revive yourself (and others) for a token amount of energy which increases exponentially with each death. Energy is also required to craft items using the Alchemy machines located throughout the town of Haven. Energy can also be exchanged for the in-game currency called crowns, or purchased directly using real money.
On June 14th, 2011, Spiral Knights (along with four other titles) were the first Free to Play titles released on Steam. This allowed people to use pre-existing accounts through Sega Pass to use old characters, or link their Steam accounts to create new characters. Achievement support was also a part of this release. As an incentive to get your Steam friends playing Spiral Knights, you can send them in-game invites to download and try the game. For each one that plays through the tutorial and gets to the main city hub of Haven, you receive a mini-tank of 15 energy. If you manage to invite five friends to do this, you are also awarded a cosmetic mask for your Spiral Knight that looks like a gas mask with the classic red Valve valve on the back.
As an added bonus, any Steam user who owns Team Fortress 2 receives a letter from Saxton Hale and his assistant Mr. Reddy upon finishing the tutorial. After unlocking the "Mission Accomplished" achievement, the player receives a congratulatory email from Mr. Hale and Mr. Reddy informing them they have earned the Spiral Sallet helmet for the Soldier class. It is a team-colored fantasy knight's helmet with a jiggleboned pouf on the back.
You can equip two weapons at a time. There are three types of weapons available: swords, guns, and bombs. You can charge all of the weapons by holding the attack button. In the case of bombs, the only way to arm a bomb is by charging it. You also have a shield that you can use to fend off attacks. Additionally, you can collect a number of attack, status and health items. As you progress, you will obtain a currency called crowns, which you can use to buy new items from merchants located throughout the game. Items level up by you gaining heat from slain enemies or treasure boxes. Heat is awarded like experience evenly between all items with each floor you complete. All items progress ten levels, needing more heat with each. Items bonuses improve at level 5 and level 10.
The dungeon floors feature random layouts, and as players explore each floor together they will encounter breakables, traps and monsters. Often, the way forward will be blocked by a gate which must be lowered via some mechanism, such as a button or toggle switch. There are also pots the players can pick up and throw, among other contraptions.
The game features an element of overarching cooperation spanning the entire community. While wading through dungeons, you will find items called 'minerals.' You can sell these minerals at gates in the Arcade area of pivotal town of Haven, and by doing so players unlock new areas to explore.
PvP combat was added in August 2011. Rather than take the traditional form of direct melee combat between players, Spiral Knights offers their own spin on arena combat with King Krogmo's Coliseum. Borrowing heavily from Bomberman, this is a grid arena with players dropping bombs (which don't need to be charged) just like Hudson Soft's classic. Free for all, team or guild team combat is offered. Player's equipment does not factor into PvP, the only way to increase your effectiveness is through collecting power-ups (again just like any Bomberman game) Players compete for coins (not crowns) to buy new gear and cosmetic bomb masks. Taking part in the arena on the initial weekend PvP was added to the game, players were awarded a cosmetic bomb mask for free. Currently there's believed to be over twenty different designs that can be either brought with coins from the new PvP vendor or gained by bidding energy on the outcome of a match to add additional prizes to either the wining team or highest scoring player.
One of the artists on the project is named Ian McConville, known for the webcomics Mac Hall (2000-2006) and Three Panel Soul (2006- ). He is responsible for creating all of the weapons in the game and the icons in the User Interface, among other things.