Amidakujiの使い方
Pair participants with outcomes at random using a classic ghost leg lottery. 2–10 people, shareable via URL.
What is Amidakuji?
Amidakuji (ghost leg lottery) is a Japanese randomization method that matches two lists by letting each participant trace a path down a ladder of vertical lines with random horizontal rungs. Decidable generates the rungs automatically for 2 to 10 participants and animates each path in color. The resulting mapping can be shared via a URL that preserves the exact rung pattern, so anyone opening the link sees the same ladder and the same outcome — perfect for "fair random" role assignments where you want everyone to verify the draw later.
使い方の手順
Enter participants
In the upper text area, list participants one per line. Pasting a spreadsheet column works directly. The tool accepts 2 to 10 names; larger groups become hard to read on the ladder, so the limit is deliberate.
Enter outcomes
In the lower text area, list the same number of outcomes (roles, prizes, win/lose, etc.). They are shown at the bottom of the ladder in input order; the mapping to participants is not yet decided.
Press Draw
Pressing "Draw" generates 10 to 18 rows of random rungs depending on participant count, then animates each person's path in color at roughly 0.5 seconds per line. The final mapping appears as a result list below.
Share the result
The share button copies a URL containing participants, outcomes, and the exact rung pattern. Anyone opening that link sees the same ladder and outcome — useful for announcing to a group or letting others verify fairness after the fact.
A concrete scenario
Four organizers divvying up year-end party duties
Situation
Four roles — venue booking, reception, MC, toast speech — need assigning across four people. Discussion gets stuck because everyone wants to avoid the MC or the speech.
How it played out
One organizer opens Decidable Amidakuji, pastes the four names up top and the four roles at the bottom, and hits Draw. Two seconds later each person is paired with a role. The share URL goes into the group chat so nobody has to remember who got what later. Thirty minutes of debate compressed into two minutes, with time reclaimed for actually planning the party.
ヒントとコツ
- Row count scales with participants: 10 rows for 2–3 people, 14 for 4–6, 18 for 7–10
- Adjacent rungs on the same row are disallowed so every path resolves uniquely
- Re-draw regenerates the pattern — use sparingly when fairness matters
- The shared URL contains the rung pattern, so results are fully reproducible
こんな時に便利
Common mistakes to avoid
- 1Participant count not equal to outcome count — the tool shows an error until they match.
- 2Extra whitespace or blank lines create phantom entries — eyeball the list after pasting.
- 3Repeatedly re-drawing until you like the result defeats the fairness. Agree on "first draw wins" up front.
- 4Forgetting to share the URL means the next visit generates a new pattern, so the original mapping cannot be reproduced.