Minesweeper Chording: How to Chord and When It Saves Clicks

Chording means clicking a number that already has all its mines flagged: every other covered square around it opens in one click. On Poozee you chord by clicking or tapping the number. It pays when flagging plus the chord costs no more clicks than opening the squares one by one. When we played thousands of boards with that rule, it cleared an Expert board in 165.4 clicks on average, against 199.0 with no flags at all and 212.7 for flagging every mine.

This guide shows how to chord, explains 3BV and efficiency (the numbers speed players use to count clicks), and measures which chords are worth making. If you are still learning what the numbers mean, start with how to play Minesweeper.

How to chord on Poozee

A chord only does something when the number of flags touching a number equals the number itself. Then it opens every covered, unflagged square around it.

Three details matter:

• Too few flags, nothing happens. Clicking a 2 with one flag around it does nothing at all, so a stray click on a number is harmless.
• A wrong flag loses the game. If the count matches but one flag sits on a safe square, the chord opens the real mine.
• Flag mode still chords. With the toggle on Flag, tapping a covered square flags it and tapping a number chords, so on a phone you can flag and chord without switching back.

You can play with the keyboard too: Tab to a square and press Enter to open it or chord it, and switch the toggle to Flag to place flags the same way.

Classic Windows Minesweeper chorded with both mouse buttons pressed together. On Poozee a plain click on the number does it, so in this guide a flag counts as one click and a chord counts as one click.

What is 3BV?

3BV (Bechtel's Board Benchmark Value) is the fewest left clicks that clear a board without flags. The definition on Authoritative Minesweeper's statistics page is simple: each opening counts one click, and each number that does not touch an opening counts one click.

• An opening is a patch of blank squares (squares with no mine around them). One click anywhere in it opens the whole patch and every number around its edge.
• A lone number touches no blank square, so no opening will ever uncover it. You have to click it yourself.

We measured 3BV on 10,000 boards per level, made by the same code as Poozee's Minesweeper with the first click in the middle:

Split into its two parts, on the same boards:

Lone numbers make up most of 3BV on every level. Boards vary a lot: Expert boards ran from 96 to 256, and 3 of the 10,000 Beginner boards had a 3BV of 1, so the first click cleared the whole board. On Poozee the first click always lands in an opening (no mine is placed on it or next to it), which classic Windows didn't promise, so other versions give slightly different numbers.

Efficiency: 3BV divided by clicks

Speed players count efficiency, also called IOE (index of efficiency): the board's 3BV divided by the clicks you actually used, with flags and chords counted as clicks. Clearing a 3BV 50 board in 50 clicks is 1.00. Without chording you can never beat 1.00, because 3BV is already the fewest left clicks possible. A good chord opens several squares for one or two clicks, and that is the only way above 1.00.

How we measured chording

We wrote a player that is perfect at logic and plays Poozee's own board code, including its real chord function. It works in rounds: it finds every square the numbers (and, near the end, the mine counter) prove safe, opens them all, and looks again. It plays every board three ways:

1. No flags (NF). It never flags. It left-clicks the safe squares, starting with the ones it knows are blank, then the ones that might be blank, and last the ones it knows hold a number, so openings get the chance to uncover numbers for free.
2. Flag all. It flags every mine as soon as it is proven, then opens squares by chording whenever a number has all its flags, and clicks a square directly only when no chord is possible.
3. Chord when it pays. It flags a mine only to chord. It makes a chord whenever flags plus the chord cost no more clicks than the covered squares it opens, the biggest saving first, and otherwise clicks.

When nothing is provably safe the player has to guess. So that every board could be measured to the end, not just the lucky ones, we let it guess right: it opened the safe square with the lowest chance of a mine, at one click in every style. All three styles reach the same stuck positions and make the same guesses, so the only difference is how they open what logic has already proven. We played 10,000 Beginner, 5,000 Intermediate and 2,000 Expert boards.

Each cell is the average number of clicks per board, and the 3BV column is the average 3BV of the same boards. Here are the same games as efficiency (3BV divided by clicks, averaged per board):

Three things stand out.

Flagging every mine was the slowest style on every level, slower even than never flagging. Each flag is a click, and many never pay it back: on Expert, 40.9% of the flag-all player's chords had only one covered square to open (a chord there saves nothing over clicking it), and 13.9% of its flags never helped any chord.

No flags could not reach 3BV. The NF player needed 2.6 more clicks than 3BV per Beginner board, 12.9 more on Intermediate and 28.1 more on Expert. It matched 3BV exactly on only 28.4% of Beginner boards. The extra clicks are numbers it opened before the blank patch next to them, which would have uncovered them for free. A perfect NF game needs you to know which safe squares are blanks, and the board often doesn't tell you in time.

Chording only when it paid beat 3BV itself on 23.1% of Beginner boards, 41.7% of Intermediate boards and 68.0% of Expert boards, and on average it took the fewest clicks of the three styles on every level.

The rule: when is a chord worth it?

Count before you flag. A chord costs one click for each mine around the number that isn't flagged yet, plus one for the chord. It replaces one click for each covered safe square around the number. Chord when the cost is no bigger than that.

Flag m and click the middle 1: two clicks open five squares. Opening them one at a time would take five clicks, so the chord saves three.

Here a chord on the second 2 would cost three clicks (flag m, flag n, chord) to open one square. Click a directly: one click.

What about a chord that only breaks even, like a 1 with one unflagged mine and two covered safe squares? Flag plus chord is two clicks, and clicking both squares is also two. We tried the threshold every way:

Clicks per board, on the same boards as above. Take the break-even chords. They cost nothing now, and the flags they leave behind can make a later chord cheaper: on Expert, taking them saved 3.5 clicks per board over chording only when it saved at least one. Waiting for big chords only was clearly worse.

Pro tip: Before you flag, glance at the covered squares around the number. If they outnumber the flags you still need to place, flag and chord. If not, click them.

Which numbers to chord: low ones

A low number needs few flags and usually has more safe squares around it, so its chord opens more. On Expert, every chord the flag-all player made, grouped by the number it clicked:

"Squares opened" includes any blank patch a chord set off. The chord-when-it-pays player came to the same answer by itself: on Expert, 68.7% of its chords were on 1s, 27.8% on 2s, 3.4% on 3s and almost none on anything higher. On 4s and higher it found a chord worth making only 67 times in 2,000 Expert boards. That is the advice of Authoritative Minesweeper's efficiency page too: low numbers favor flagging and chording, high numbers favor plain clicks.

High 3BV boards reward chording most

Not every board gains the same. We split the Expert boards into thirds by 3BV. On the third with the lowest 3BV (150.3 on average), chording when it paid saved 26.2 clicks per board over no flags. On the highest third (191.8 on average) it saved 41.9. On Beginner the gap almost disappears: 0.2 clicks on the lowest third, 2.9 on the highest.

That matches the advice on Authoritative Minesweeper's efficiency page: boards with lots of openings (low 3BV) suit no-flags play, while boards crowded with numbers (high 3BV) suit flagging and chording. In practice:

• Beginner: the saving is small (1.4 clicks per board in our test), so don't let counting slow you down. Chord the easy 1s and click everything else.
• Intermediate and Expert: chord on purpose. Look for 1s and 2s along the edge of an open area, flag only the mines those chords need, and leave the other mines unflagged.

Efficiency is not the only thing that matters for speed: a chord that makes you stop and count can cost more time than the click it saves. Use the counting rule slowly until it becomes a glance, then speed up.

Keep playing

Try it now in Minesweeper: play an Intermediate board chording only when the covered squares outnumber the flags you still need, then play one with no flags, and see which felt faster. Chording works best once you read the board quickly, so practice the Minesweeper patterns like 1‑2‑1 and 1‑2‑2‑1. And when logic runs out, our guide to Minesweeper 50/50s shows how to guess well.