Rules Codex

Rules Codex

A permanent cache of dice rules, core mechanics, combat, and conditions — everything a table needs, no AI involved, printable for the tabletop.

Tabletop Rules Codex

vOctober 2026

Dice & Rolling

The Dice Family

Standard polyhedral dice: d4 (four-sided, read the number at the bottom point), d6 (cube), d8, d10 (read the higher of the two zero-to-nine sets; a second d10 in tens reads 00–90 for d100), d12, and d20 (the standard action die). Percentile dice (d100) use a tens die plus a ones die — 00 + 0 means 100.

Dice Notation

"XdY+Z" means roll X dice with Y sides and add Z. 2d6+3 → roll two six-sided dice, sum them, add 3. "XdYkh" (keep highest) is common for character creation: 4d6kh3 → roll four d6, keep the best three, sum them — the classic ability-score method.

When to Roll

Roll only when the outcome is uncertain and failure is interesting. Automatic successes don't need dice — a character can walk across a room. Set the stakes first: what happens on a success, and what happens on a failure, before the dice hit the table.

Advantage & Disadvantage

When circumstances favor a roll, roll two d20 and keep the higher (advantage). When circumstances hinder it, roll two d20 and keep the lower (disadvantage). Multiple sources don't stack — you either have advantage, disadvantage, or neither. They cancel each other out.

Luck & Inspiration

Many tables award a "luck point" or inspiration for great roleplay or clever play. Spending one usually lets a player reroll a die and keep the better result, or turn a failed roll into a success at a dramatic moment. Give them sparingly — they should feel special.

Fudging & Hiding Rolls

The game master may roll in the open or behind a screen. Behind the screen lets the GM quietly soften a lethal random result, but rolling in the open builds trust. Agree on the table's culture before the first session.

Core Mechanics

Ability Scores

The six universal abilities: Strength (raw power, lifting, melee force), Dexterity (agility, reflexes, balance, aim), Constitution (health, stamina, resisting poison and fatigue), Intelligence (memory, reasoning, lore), Wisdom (perception, intuition, insight), Charisma (presence, persuasion, performance). Typical adventurer scores range 8–18.

Ability Modifiers

Modifier = (Score − 10) ÷ 2, rounded down. Score 10–11 → +0, 12–13 → +1, 14–15 → +2, 16–17 → +3, 18–19 → +4, 20–21 → +5. The modifier, not the score, is what you add to rolls.

The d20 Test

Roll a d20, add the relevant ability modifier (and proficiency bonus if trained), and compare to a Difficulty Class (DC). Meet or beat the DC → success. A natural 20 on the die is usually a critical success; a natural 1 is usually an automatic failure — house-rule both to taste.

Difficulty Classes

Suggested DCs: 5 very easy, 10 easy, 12 medium, 15 hard, 20 very hard, 25 nearly impossible, 30 godlike. When in doubt, pick 10 for routine checks and 15 for anything dramatic.

Proficiency

A proficiency bonus reflects training: typically +2 at level 1, growing to +6 at high level. You add it to things you are trained in — skills, saving throws, attacks with practiced weapons, and your spell style — never to everything at once.

Skills & Checks

Common skill families: Athletics (STR), Acrobatics & Stealth (DEX), Arcana, History, Investigation, Nature (INT), Animal Handling, Insight, Medicine, Perception, Survival (WIS), Deception, Intimidation, Performance, Persuasion (CHA). The GM picks the ability that fits the approach — a Intimidation attempt can be STR as easily as CHA.

Working Together

Two characters can cooperate on a task: the helper rolls first; on DC 10, the lead gets advantage. Aid has limits — a helper needs to be genuinely capable, and some tasks can't be shared.

Short & Long Rests

A short rest (about an hour) lets characters spend hit dice to heal and refresh minor abilities. A long rest (a night's sleep, ~8 hours) restores all hit points, roughly half the party's hit dice, and resets major abilities. Pace adventures around how many rests the group earns.

Combat

The Combat Round

One round ≈ 6 seconds. Every combatant gets a turn in initiative order. On your turn you can move (up to your speed, in any combination with actions) and take one action, plus possibly one bonus action and one reaction.

Initiative

Roll initiative once per encounter: a Dexterity check, usually d20 + Dexterity modifier. Highest acts first; ties broken by Dexterity score, then by agreement or a coin flip.

Attacks

Attack roll: d20 + ability modifier + proficiency (if trained with the weapon) vs. the target's Armor Class. Melee weapons usually use Strength; finesse and ranged weapons use Dexterity. On a hit, roll the weapon's damage dice and add the modifier.

Damage, Healing & Zero HP

Subtract damage from hit points; healing restores them. At 0 HP you fall unconscious and start making death saves: on your turn, roll d20 — three successes before three failures stabilizes you; three failures means death. Taking damage while down causes an automatic failure (two if a critical hit). Reaching 0 HP but surviving with positive HP afterward resets the tally.

Actions in Combat

Standard action menu: Attack (strike or shove/grapple), Cast a Spell, Dash (double movement), Disengage (avoid opportunity attacks), Dodge (attackers roll against you with disadvantage), Help (grant an ally advantage), Hide, Ready (hold an action for a trigger), Search, or Use an Object.

Bonus Actions & Reactions

Bonus actions come from specific abilities — you only get one per turn, and only if something grants it. Reactions happen outside your turn, once per round, typically an opportunity attack when an enemy leaves your reach, or a readied action triggering.

Cover & Ranged Combat

Half cover (+2 AC), three-quarters cover (+5 AC), total cover (can't be targeted directly). Ranged attacks at a target in an enemy's reach suffer disadvantage. Shooting into a melee is normally fine unless your table uses friendly-fire house rules.

Mounts, Size & Movement

Tiny creatures occupy 2.5 ft, small/medium 5 ft, large 10 ft, huge 15 ft, gargantuan 20 ft. Difficult terrain costs double movement. Climbing and swimming cost extra unless you have a movement speed for it. Falling deals 1d6 damage per 10 feet fallen, to a usual cap of 20d6.

Conditions of War

Track the condition list (see the Conditions section) on the sheet during a fight. Most conditions are both a penalty and a story: restrained means tangled in a net, frightened means fleeing the dragon's roar — describe them, don't just apply them.

Conditions

Blinded / Deafened

Blinded: can't see — attacks against you have advantage, your attacks have disadvantage, and you can't rely on sight-based Perception. Deafened: can't hear — auto-fail any ability check that requires hearing.

Charmed / Frightened

Charmed: a charmer can verbally command you with advantage on social interaction, and you can't attack the charmer. Frightened: disadvantage on ability checks and attacks while the source of fear is in view, and you can't willingly move closer to it.

Grappled / Restrained

Grappled: your speed becomes 0. Restrained: speed 0, attacks against you have advantage, your attacks and Dexterity saves have disadvantage. Escaping a grapple or restraint is usually an Athletics or Acrobatics contest against the grappler.

Incapacitated / Paralyzed / Stunned / Unconscious

Incapacitated: can't take actions or reactions. Paralyzed: incapacitated plus can't move or speak, and attacks from within 5 ft that hit are criticals. Stunned: incapacitated, can't move, auto-fail STR and DEX saves, attacks against you have advantage. Unconscious: incapacitated, prone, drops everything, auto-fails STR and DEX saves.

Invisible / Petrified / Poisoned / Prone

Invisible: unseen — attacks against you have disadvantage, your attacks have advantage. Petrified: turned to stone, incapacitated, damage resistance, auto-fail all saves. Poisoned: disadvantage on attack rolls and ability checks. Prone: only crawling movement, attacks against you within 5 ft have advantage, ranged attacks against you have disadvantage; standing costs half your speed.

Character Creation

Rolling vs. Buying Scores

The classic methods: roll 4d6, keep the best 3, six times (classic swing); or point buy — a budget of 27 points where a score costs its modifier above 8 (8=0, 10=2, 14=7, 15=9). Standard array (15, 14, 13, 12, 10, 8) is the fast, fair default. Ask the table which one everyone uses.

Assigning Scores to Abilities

Put your highest score in the ability your role leans on (fighters → Strength or Dexterity, spellcasters → their casting ability), your second in Constitution — hit points keep everyone alive — and dump the lowest somewhere your concept can absorb (a bookish wizard can dump Strength).

Concept First, Sheet Second

Write one sentence of concept before touching numbers: "a disgraced knight hunting the lie that ruined her." Then choose the class and scores that make the sentence true. A sheet built from a concept plays better than a sheet built from an optimizer.

Backstory Hooks That Pay Off

Give the GM three hooks on the sheet: a person you care about, a place you can't return to, and a thing you want. Short beats long — three vivid lines beat three paragraphs the GM never reads.

Leveling Up

On a level up: add the new hit points (hit die roll or average + CON modifier), increase the proficiency bonus on milestone levels (5, 9, 13, 17), gain new abilities per your game's table, and if a level grants an ability score improvement, raise one score by 2 or two scores by 1 (or take a feat, if the table allows).

Equipment & Wealth

Starting Gear

A practical starting kit: a weapon you're trained with, armor you can move in, a ranged option or backup blade, rope (50 ft), torches or a lantern with oil, rations for the trip, a healing potion or two, and coin. Write the weight only if the table tracks it.

Armor Class From Gear

Unarmored: 10 + Dexterity modifier. Light armor: base 11–12 + full Dexterity. Medium: base 13–14 + Dexterity capped at +2. Heavy: 16–18 flat, no Dexterity bonus but no penalty. Shields add +2. Heavier armor trades agility for protection — pick by concept, not just AC.

Coins & Currency

Common ladder: 10 copper = 1 silver, 10 silver = 1 gold. Typical inn stay 5 silver–1 gold, a decent meal 1–5 silver, a riding horse ~50 gold, a suit of plate armor ~1,500 gold. Keep treasure in coin and gems — loot that can't be spent is just flavor.

Carrying Capacity

Simple rule: you can carry Strength × 15 in pounds without slowing down. Encumbrance variants halve movement at half capacity. Most tables eyeball it — a character "reasonably" carries a weapon, armor, pack, and a few trophies; a dragon hoard is a logistics problem.

Light & Dark

Bright light: normal vision. Dim light (torches at the edge, dusk): Perception relies on sight has disadvantage. Darkness: effectively blinded unless you have darkvision (see in dim light as if bright, usually 60 ft) or a light source. Count torch hours — darkness is a timer.

Spells & Magic

How Casting Works

You know a set of spells; each has a level from 1–9. To cast one, expend a spell slot of that level or higher — slots are the day's fuel, restored on a long rest (and sometimes short rest for some traditions). Casting a spell at a higher slot usually makes it stronger ("upcasting").

The Spellcaster Archetypes

Prepared casters (clerics, wizards) choose which spells are ready each day — flexible but bookkeeping-heavy. Spontaneous casters (sorcerers, bards) know fewer spells permanently but cast them freely — limited but fast. The difference shapes how each player plans a day.

Concentration

Powerful spells require concentration: only one at a time. Taking damage forces a Constitution saving throw (DC 10, or half the damage taken, whichever is higher) or the spell ends. Being incapacitated or killed ends it. Remind the table: two concentration buffs don't stack.

Rituals & Components

A spell lists components: verbal (spoken, can't be gagged), somatic (hand free), material (a listed item or a component pouch/focus covers most). Spells with a ritual tag can be cast as a ritual — 10 extra minutes, no slot spent — perfect when time isn't the enemy.

Counterspell & Magic Duels

When another caster acts, reactions like counterspell interrupt the casting — resolve the reaction first. For homebrew duels, opposed casting-ability checks with spells as stances keep it cinematic without a rulebook of exceptions.

Exploration & Downtime

Dungeon Time, Torch Time

In exploration play, track turns (about 10 minutes each) rather than minutes. Every few turns: torches burn down, wandering-monster rolls, and the map gets another room. Time pressure is what turns a dungeon from a tour into a heist.

Traps & Hazards

A good trap telegraphs: scorch marks, a suspicious floor, dripping hinges. Detection is a Perception check against the trap's DC; disabling is thieves' tools + Dexterity. Damage traps deal dice scaled to deadliness — 1d10 minor, 2d10 dangerous, 4d10 or more deadly.

Travel Pace

On foot: slow 2 miles/hour (stealthy, observant), normal 3, fast 4 (less alert). Difficult terrain (hills, forest, snow) halves all of it. For each day of travel, roll once for navigation, once for encounters — and ask who is on watch at night.

Weather & Environment

Cold: below freezing, a DC 10 CON save per hour unprotected or gain a level of exhaustion. Heat: DC 5 CON save per hour in heavy gear. Exhaustion stacks: disadvantage on checks → speed halved → disadvantage on attacks and saves → half HP → speed 0 → death. It clears one level per long rest.

Downtime & Between Sessions

Between adventures, a week of downtime buys one project: training a tool or language, carousing for rumors, researching a mystery, crafting mundane items, or spending coin on lifestyle — which quietly sets the table's social texture. One roll, one result, keep it moving.

Social Encounters

Run NPCs with an attitude (hostile, indifferent, friendly) and a want. Checks adjust attitude: Persuasion shifts a step on a success, Deception risks collapse on a failure. Roleplay first, roll second — the roll prices the scene, the roleplay earns it.

GM Quick Reference

Balancing Encounters

A rough gauge: a "medium" fight is one monster whose XP value ≈ one PC's level × 100, or several monsters totaling about half the party's combined level × 100 in XP. Deadly is roughly double. Adjust for action economy — six weak monsters outnumber and out-react one big one.

Monster Stat Blocks On the Fly

Any creature needs only: AC, hit points (hit dice + CON), one attack (+to hit, damage dice), a save DC or two, and a movement speed. reskin anything — a "bandit lord" is a bandit with more hit dice and a name. Invent at the table; the screen is yours.

Passive Scores

Passive Perception = 10 + all modifiers (advantage adds +5, disadvantage −5). Use it to decide what characters notice without declaring a search — traps, ambushes, and hidden doors compare against it silently.

Saves by Deadliness

Set save DCs from the caster's ability: 8 + proficiency + modifier. For hazards, lean on the DC ladder. Give stronger creatures higher DCs, and always ask "what does a failure cost?" before calling for the roll.

NPC Attitudes & Reactions

2d6 reaction roll works everywhere: 2–5 hostile, 6–8 wary or uncertain, 9–12 friendly. Modifiers from reputation, gifts, and approach. Roll it when the party meets someone new and let the dice argue for a surprise.

Table Craft

The Session Zero

Before play: agree on tone (heroic vs. grim), content boundaries ("lines and veils"), session length, who brings snacks, and how absent players' characters behave. Ten minutes here prevents ten hours of friction later.

Improvising NPCs

Give every named NPC one want, one fear, and one quirk. The quirk makes them playable instantly (a nervous habit, a verbal tic); the want and fear make them reusable when the party circles back three sessions later.

The Rule of Yes, And…

Player ideas the rules don't cover: say "yes, and" when it's fun and plausible, "yes, but" when it should cost something, and "no, because" only when it would break the fiction. Never make a player roll for something a competent person could just do.

Tracking Time & Travel

Track overland travel in half-day legs. For each leg, roll or adjudicate: navigation (do you get lost?), foraging (do you eat?), and encounters (is the road empty?). Resource attrition — torches, rations, arrows — is what makes wilderness feel real.

Loot & Treasure

Mix coin (flexible), gear (useful), and strange items (memorable). A good hoard: one useful mundane item, one piece of lore, one magic item or map, and enough coin to matter. Hand out wealth early — shopping is a whole session of fun.

Ending on a Cliffhanger

Stop the session on a question, not an answer — a door opening, a name spoken, a choice unmade. Players think about the table all week when the last beat is a hook instead of a campfire.

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