Codex

A d20 character sheet that runs the 3.5 rules for you - and tells you when your character breaks them.

Overview

Codex is a browser-based character sheet and encounter tracker for d20 games using the 3.5 SRD, published under the Open Game License v1.0a. It runs as a progressive web app: it installs on a phone like a native app, works with no connection, and pushes any pending changes once the network returns. The design goal is that the sheet does the arithmetic a table normally does by hand. Underneath the interface sits a full implementation of the 3.5 ruleset - typed bonus stacking, iterative base attack bonuses, multiclassing, spell slots derived per ability score, two-weapon fighting, armour check penalties, encumbrance, size modifiers and confirmable criticals - rather than a set of fields the player has to total up. Every value on the sheet is derived, and clicking any ability, save, skill or weapon rolls it with the correct modifier already applied. Codex also checks the character against the rules and says so when something does not add up. If a sheet ends up with more skill ranks than the character's level allows, more feats than available slots, spells prepared that the caster can no longer cast, a cleric missing his two domains or a paladin who has stopped being Lawful Good, the sheet reports it and links to the tab where it is fixed. It never edits the character on its own - the correction is always the player's decision. The Encounter tab turns the same engine into a combat tracker: initiative order, a bestiary of 466 SRD creatures, per-combatant conditions, a battle grid with flanking, reach and range increments, and an encounter difficulty estimator. Encounters can be run solo or as a shared room, where a server validates every action rather than trusting the client. Characters can be built by hand or generated. Thirty-two archetype templates - twenty of them multiclass - produce a complete, rules-legal character at any level, with equipment bought from the wealth the SRD grants for that level and restricted to what the character is actually proficient with. Codex is bilingual (English and Spanish), free to use, and requires no installation or account to try.

Key features

A real 3.5 engine, not a form

Typed bonus stacking, iterative attacks, multiclassing, spell slots by ability score, two-weapon fighting, armour check penalties and encumbrance are all derived from the character, not typed in by the player.

It tells you when the character is illegal

Ranks over the cap, feats without prerequisites, spells above the caster's level, missing cleric domains, an alignment a class does not allow - flagged with the exact numbers and a link to where it is fixed. Nothing is changed automatically.

Encounter tracker with a battle grid

Initiative, 466 SRD creatures, conditions per combatant, flanking, reach, range increments and a difficulty estimator. Playable alone or in a shared room with server-side validation.

One-click character generation

32 archetype templates, 20 of them multiclass, from level 1 to 20. Ability scores, hit points, feats, skills, spells, domains and gear bought within the level's wealth.

Full spell and feat catalogues

605 SRD spells and 123 feats, searchable, with a wizard's spellbook, daily preparation, specialist schools with prohibited schools, metamagic and spontaneous conversion.

Works offline, installs like an app

Progressive web app with a service worker and a save queue that drains when the connection returns. Autosave uses optimistic locking, so editing from two devices never silently loses data.

Bilingual

Complete English and Spanish, switchable at any time and remembered between sessions.

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