Chording is a way to clear multiple tiles at once. Instead of clicking each safe tile one by one, you click a numbered tile that already has the right number of flags around it, and the game clears all remaining neighbors in one shot.
If a "3" has three adjacent flags, chording that tile instantly reveals every unflagged tile around it. One click does the work of five or six. Once you start using it, going back to clicking individual tiles feels painfully slow.
In classic minesweeper, you chord by pressing both mouse buttons at the same time on a numbered tile (or middle-clicking, depending on the version). The game checks whether the number of adjacent flags matches the tile's number. If they match, it clears the rest.
In m3o, chording is built into the default controls. Left click any numbered tile to clear the unflagged neighbors, or right click it to flag them. No special gesture required -- just play normally and chording happens when the conditions are right.
Chording works when the number of flags around a tile equals the tile's number. A "2" with two adjacent flags? Chord it. A "4" with only three flags placed? Nothing happens yet.
The risk is real: if any of those flags are wrong, chording will open a mine and end your game. Chording trusts your flags completely. So before you chord, make sure your logic is solid. A misplaced flag turns a speed trick into a game-ending mistake.
Good situations to chord:
Obvious corners where a "1" has one flag and several unopened tiles
Chain reactions where chording one tile reveals numbers you can immediately chord again
Cleared borders where you've worked out a section and just need to sweep up the remaining safe tiles
Competitive minesweeper players use a technique called the 1.5 click to combine flagging and chording into a single fluid motion. You right-click to place a flag, then without releasing, press the left button to immediately chord the adjacent numbered tile. Two actions, one smooth movement.
The name comes from the idea that you're doing one and a half clicks instead of two separate ones. In practice it cuts a huge amount of wasted mouse travel and shaves seconds off your time on Expert boards.
This technique matters most in classic minesweeper where flagging and chording are separate inputs. In m3o, the controls already collapse these steps -- a left click on a satisfied number just clears, a right click flags -- so you get the speed benefit without learning the finger gymnastics.
Chording is easy to understand but takes practice to use instinctively. A few things that help:
Flag as you go. If you wait until the end to flag, you miss chording opportunities along the way. Place flags the moment you're certain.
Scan for satisfied numbers. After placing a flag, check every number touching it. One flag often satisfies multiple tiles at once.
Chain your chords. Chording reveals new tiles, which reveal new numbers, which might already be satisfied. Look for the next chord before you've finished processing the first.
Don't force it. If you're not sure about a flag, don't place it just to chord faster. Speed means nothing if you open a mine.
The players at the top of minesweeper leaderboards chord constantly. It's not an advanced trick reserved for experts. It's a basic mechanic that most players never discover, and the gap between knowing it and not knowing it is enormous.
If you want to practice, m3o is a good place to build the habit. The board is infinite, so there's always more to clear, and you can see how your speed stacks up on the leaderboards.