Dice System

A detailed explanation of the dice roll mechanics at the core of TRPG and how judgments work in this app.

What is the Dice System?

In TRPGs, dice are used to determine the success or failure of actions. This is the foundation of the "dice system."

Why Use Dice?

Dice serve three important roles:

Randomness - Creates unpredictable developments
Fairness - Same probability for everyone
Drama - The excitement of critical hits!

Types of Dice

TRPGs use dice with various numbers of faces.

Basic Dice

Dice	Name	Faces	Purpose
🎲 d4	Tetrahedron	4 faces	Small damage
🎲 d6	Cube	6 faces	General checks
🎲 d8	Octahedron	8 faces	Medium damage
🎲 d10	Decahedron	10 faces	Percentages
🎲 d12	Dodecahedron	12 faces	Large damage
🎲 d20	Icosahedron	20 faces	Main checks

Dice Used in This App

Primarily uses the d20 (20-sided die).

1d20 = Roll one 20-sided die
2d6 = Roll two 6-sided dice
3d4+2 = Roll three 4-sided dice and add 2

How Checks Work

Basic Check Flow

1. Player declares action
   ↓
2. GM sets difficulty (DC)
   ↓
3. Roll d20
   ↓
4. Add modifiers
   ↓
5. Compare to target
   ↓
6. Success or failure

Concrete Example

Situation: You want to force open an old door

Player: "I kick the door down!"

GM: "Make a Strength check, DC 15"

[Roll d20 → Result: 12]

Character's Strength modifier: +3

Total: 12 + 3 = 15

Result: Success! The door opens.

Difficulty Class (DC) Guidelines

The GM sets a DC (Difficulty Class) based on task difficulty.

DC	Difficulty	Description
5	Very Easy	Almost never fails
10	Easy	Average person succeeds
15	Medium	Requires some skill
20	Hard	Expert level
25	Very Hard	Even masters may fail
30	Nearly Impossible	Legendary feat

DC in This App

AI GM automatically sets based on situation.

Opening a door → DC 12-15
Finding a trap → DC 15-18
Persuading a dragon → DC 25+

Modifiers

Numbers added to dice rolls.

Main Modifiers

1. Ability Score Modifiers

Calculated from character ability scores.

Ability Score → Modifier
8-9 → -1
10-11 → 0
12-13 → +1
14-15 → +2
16-17 → +3
18-19 → +4
20 → +5

2. Skill Modifiers

Expertise in specific areas.

Lockpicking skill → Added to lock-picking checks
Magical knowledge → Added to magic checks
Negotiation → Added to persuasion checks

3. Circumstantial Modifiers

Bonuses/penalties based on current situation.

Favorable conditions (+2 to +5):

Attacking from high ground
Ally support
Using appropriate tools

Unfavorable conditions (-2 to -5):

Acting in darkness
Injured state
Time pressure

Criticals

Critical Hit (Great Success)

When d20 rolls 20:

Automatic success
Special bonus effects
Dramatic description

Example: Critical hit in combat
→ Damage doubled!
→ Enemy's armor destroyed!

Critical Miss (Great Failure)

When d20 rolls 1:

Automatic failure
Something bad happens
Comic description (sometimes dangerous)

Example: Critical miss with sword attack
→ Sword slips and cuts your foot!
→ Drop your weapon!

Advantage & Disadvantage

Adopts D&D 5e-style rules.

Advantage

Roll two d20s and take the higher result

[Roll d20 twice]
Result 1: 8
Result 2: 15

→ Take 15!

Conditions:

Ally assistance
Enemy unaware
Perfect preparation

Disadvantage

Roll two d20s and take the lower result

[Roll d20 twice]
Result 1: 18
Result 2: 5

→ Take 5...

Conditions:

Injured
Poor visibility
Unstable footing

Dice Rolling in This App

Automatic Processing

AI GM automatically rolls dice

Your tasks:

Declare action
Watch results

AI GM's tasks:

Select appropriate dice
Set DC
Execute roll
Describe results

3D Dice Animation

Dice rolls feature 3D physics engine for realistic behavior.

Realistic rolling
Clicking sounds
Result highlighting

Checking Results

Dice roll results appear in chat log.

🎲 Dice Roll: d20 + modifier
Result: [15] + 3 = 18
Check: Success! (DC 15)

Frequently Asked Questions

Q: Can I roll dice myself?

A: In the current version, AI GM rolls automatically. This ensures a fair game without cheating.

Q: My luck is too bad to clear

A: AI GM detects consecutive failures and adjusts difficulty or suggests alternative solutions.

Q: What's the critical probability?

A: 5% (1 in 20). Same as rolling any specific number on d20.

Q: Can I see the dice results?

A: Yes, all dice rolls are transparent. Results are displayed in chat.

Strategic Dice Usage

1. Risk Management

Avoid high DC checks when possible

Find alternative approaches
Prepare before attempting
Get ally help

2. Increase Modifiers

Ways to improve success rate:

Equipment that boosts abilities
Learn appropriate skills
Create favorable situations

3. Save Abilities for Important Moments

Many TRPGs have once-per-day special abilities. Save them for boss battles.

Next Steps

Now that you understand the dice system, try actually playing:

Character Creation - Optimize modifiers
Scenarios Guide - Best scenarios for practice
What is TRPG - Review the basics

🎲 Good luck! May the dice be ever in your favor!