root@generate-random:~/d20-roller$ _

D20 Dice Roller

Roll a virtual 20-sided die with modifiers, advantage, and disadvantage for D&D, Pathfinder, and tabletop RPG games

Our D20 dice roller simulates rolling a 20-sided die instantly for D&D 5e, Pathfinder, and all d20 System games. Roll with advantage, disadvantage, or apply modifiers for attack rolls, skill checks, and saving throws. Perfect for online D&D sessions, character creation, and quick tabletop RPG dice rolls when physical dice aren't available.

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$ generate --type=dice --notation=2d6+3

D&D DICE ROLLER →

Complete D&D dice roller with all seven polyhedral dice, stat rolling (4d6 drop lowest), and preset common D&D rolls for character creation and gameplay.

$ generate --type=dice --notation=4d6dl1

What is a D20 Dice Roller?

A D20 dice roller is a virtual tool that simulates rolling a 20-sided die (icosahedron), the most iconic die in tabletop role-playing games. The d20 is the core mechanic in Dungeons & Dragons, Pathfinder, and all d20 System games, used to determine the success or failure of actions including attack rolls, ability checks, and saving throws. When you roll a d20 and add modifiers from your character's abilities and proficiencies, you compare the total to a target number (Difficulty Class or AC) to determine success.

Our online d20 roller provides instant random results equivalent to rolling a physical 20-sided die, with additional features for modern RPG mechanics like advantage (roll 2d20, keep highest), disadvantage (roll 2d20, keep lowest), and automatic modifier calculation. The tool is cryptographically random and displays roll statistics, making it perfect for online D&D sessions on platforms like Roll20, Foundry VTT, or Discord where players need quick, transparent dice rolls that everyone can see.

D20 Roller Configuration Options

Number of Rolls (1-100)

Generate multiple d20 rolls at once for batch processing. Roll 1 die for a single check, or generate 10-50 rolls for pre-rolling attack sequences, ability checks, or random encounter tables. Bulk rolling saves time during combat and speeds up gameplay.

Modifier (-20 to +20)

Add or subtract a modifier to each d20 roll to account for ability scores, proficiency bonuses, magic items, and situational bonuses. Common modifiers range from -5 to +15 depending on character level and stats. The tool automatically calculates the final total (d20 roll + modifier) for instant results.

Roll Mode: Normal

Standard d20 roll without special mechanics. Roll one 20-sided die and apply the modifier. This is the default mode used for most d20 System checks, attacks, and saves when no advantage or disadvantage applies.

Roll Mode: Advantage

D&D 5e mechanic where you roll 2d20 and keep the highest result. Advantage is granted by helpful conditions, flanking, or abilities. The tool automatically rolls two d20s, displays both results, shows which die was kept (highest), and which was discarded (lowest), then applies your modifier to the kept roll.

Roll Mode: Disadvantage

D&D 5e mechanic where you roll 2d20 and keep the lowest result. Disadvantage is imposed by hindering conditions, attacking while prone, or enemy abilities. The tool rolls two d20s, keeps the lowest, discards the highest, and applies your modifier to the final result.

Roll Statistics & Export

View aggregate statistics including total rolls, average result, highest roll, and lowest roll. Export all results as TXT, CSV, or JSON for campaign logs, statistical analysis, or integration with virtual tabletop software. Perfect for tracking player luck over time or analyzing dice distribution.

How to Roll a D20 Online

[STEP 1] Set Number of Rolls

Choose how many d20 rolls you need (1-100). Use 1 for a single check, 5-10 for multiple attack rolls in combat, or 20+ for pre-rolling random tables or batch skill checks. The tool generates all rolls instantly.

[STEP 1] Add Modifier

Enter your modifier from -20 to +20 based on your character's stats. For example, a +7 modifier for a level 5 rogue with +5 DEX and +2 proficiency bonus on Stealth checks. The tool automatically adds the modifier to each roll and displays both the natural d20 result and the total.

[STEP 1] Select Roll Mode

Choose Normal (1d20), Advantage (2d20 keep highest), or Disadvantage (2d20 keep lowest) based on the situation. The tool shows which die was kept and which was discarded for advantage/disadvantage rolls, maintaining full transparency.

[STEP 1] Generate & Use Results

Click EXECUTE GENERATION to roll the dice. View individual roll results with highlighting for critical hits (20) and critical failures (1). Copy individual rolls or export all results as TXT, CSV, or JSON for virtual tabletop integration.

D20 Rolling Best Practices

_ Declare your roll before rolling - State what you're rolling for (attack, skill check, save) and the modifier before clicking generate for transparency in online games.
_ Use advantage/disadvantage correctly - Only apply advantage or disadvantage when granted by game mechanics, not for general "luck" rolls. They don't stack in D&D 5e.
_ Double-check your modifier - Verify your modifier calculation includes ability modifier + proficiency bonus + situational bonuses before rolling to avoid errors.
_ Export for record-keeping - Save important rolls (character death saves, critical story moments) using the export feature for campaign logs and memories.
_ Roll openly in online games - Share your roll results in Discord, Roll20, or Foundry chat to maintain trust and transparency with your DM and party.
_ Respect critical hits and fails - Natural 20s are critical hits (automatic success) and natural 1s are critical failures in most d20 systems - honor these special rolls.

Technical Implementation

Our D20 roller uses cryptographically secure random number generation (CSPRNG) to simulate fair, unbiased dice rolls equivalent to rolling physical 20-sided dice. The algorithm implements advantage and disadvantage mechanics precisely as specified in D&D 5e rules:

Algorithm: D20 Roll with Advantage/Disadvantage

1. Initialize: Set die_size = 20, dice_count = 1 (normal) or 2 (adv/dis)
2. Generate: Use CSPRNG to generate dice_count random integers ∈ [1, 20]
3. Apply Roll Mode:
   - Normal: result = roll[0]
   - Advantage: result = max(roll[0], roll[1]), discard = min(roll[0], roll[1])
   - Disadvantage: result = min(roll[0], roll[1]), discard = max(roll[0], roll[1])
4. Calculate: final_total = result + modifier
5. Flag: critical_hit = (result == 20), critical_fail = (result == 1)
6. Return: {natural_roll: result, total: final_total, discarded, critical}

// Probability distribution:
// Normal d20: P(x) = 5% for each outcome (1-20)
// Advantage: P(x) = (2x-1)/400 (favors higher rolls)
// Disadvantage: P(x) = (41-2x)/400 (favors lower rolls)

API Access for Developers

GET https://generate-random.org/api/v1/generate/dice?notation=1d20&modifier=5&count=10

VIEW FULL API DOCUMENTATION →

Frequently Asked Questions

What is a D20 and why is it used in RPGs? ▶

A D20 is a 20-sided die (icosahedron) that serves as the core randomizer in d20 System games like Dungeons & Dragons and Pathfinder. It provides a linear probability distribution where each outcome (1-20) has an equal 5% chance. The d20 is used for attack rolls, ability checks, and saving throws because its range (1-20) allows modifiers to meaningfully affect success rates against target numbers (DC/AC) typically ranging from 10-30, creating a skill-based probability system where character stats matter.

How does advantage work in D&D 5e? ▶

Advantage means you roll two d20s and use the higher result. When you have advantage on an attack roll, ability check, or saving throw, roll 2d20, keep the highest die, discard the lowest, then add your modifier. Advantage significantly increases your chance of success - for example, rolling 11+ on a normal d20 is 50%, but with advantage it increases to 75%. Our tool automatically rolls both dice, highlights which die was kept, and shows the discarded die for full transparency.

How does disadvantage work in D&D 5e? ▶

Disadvantage means you roll two d20s and use the lower result. When you have disadvantage, roll 2d20, keep the lowest die, discard the highest, then add your modifier. Disadvantage significantly decreases your chance of success - rolling 11+ drops from 50% (normal) to 25% (disadvantage). Common sources of disadvantage include attacking while prone, being blinded, or attacking a hidden enemy. The tool shows both dice rolled and which was kept vs. discarded.

What is a critical hit on a D20? ▶

A critical hit (or "natural 20" or "nat 20") occurs when you roll exactly 20 on the die before applying modifiers. In D&D 5e, a critical hit on an attack roll means the attack automatically hits regardless of AC, and you roll double the normal damage dice. Our tool highlights natural 20s in green to make them easy to spot. Some abilities or magic items expand the critical range (18-20), but standard rules only count natural 20s.

What is a critical failure on a D20? ▶

A critical failure (or "natural 1" or "nat 1") occurs when you roll exactly 1 on the die before modifiers. In D&D 5e, a natural 1 on an attack roll means the attack automatically misses regardless of your modifier or the target's AC. Some DMs apply additional consequences for natural 1s (dropping weapons, hitting allies) as house rules, though this isn't in the official rules. Our tool highlights natural 1s in red.

Can advantage and disadvantage stack or cancel out? ▶

No, advantage and disadvantage do not stack in D&D 5e. If you have multiple sources of advantage, you still only roll 2d20 (not 3d20 or more). If you have both advantage and disadvantage from any number of sources, they cancel each other out completely and you roll a normal 1d20. For example, if you're attacking while hidden (advantage) but the target is prone (disadvantage on ranged attacks), you roll a normal single d20.

How do I calculate my D20 modifier? ▶

Your d20 modifier is the sum of your ability modifier + proficiency bonus (if proficient) + any situational bonuses. For example, a level 5 Rogue making a Stealth check would add: DEX modifier (+5 if DEX is 20) + proficiency bonus (+3 at level 5) + any magic item bonuses = total modifier. Enter this total in our modifier field, and the tool automatically adds it to each d20 roll, displaying both the natural roll and the final total.

Are online dice rollers fair and random? ▶

Yes, when they use cryptographically secure random number generation (CSPRNG) like our tool does. CSPRNG algorithms are designed to be unpredictable and unbiased, equivalent to rolling fair physical dice. Each outcome (1-20) has exactly a 5% probability, and past rolls don't influence future rolls. Our tool is transparent - it shows every roll result immediately, and you can export rolls to verify the distribution matches expected probabilities over large sample sizes.