Codex

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.