The second screen for Isaac players who don’t run mods.

Isaac Codex is a companion app for The Binding of Isaac. Every item, character and boss, with numbers produced by running experiments inside the game rather than copied from a wiki. Plus a quiz, a daily puzzle, a progress tracker that tells you what to unlock next, and an assistant that only answers from that data.

iOS and Android. Offline first, opens in a second. English and Chinese.

Sad Onion

collectible:1

Rebirth, quality 1, passive

Stat	Measured
Tears	2.73 → 3.43 (+0.70)
Damage	no change
Pool	Treasure Room

Verified in-game, run E1-000001

Fires faster. One of the plainest upgrades in the game and one of the best on the first floors.

Measured on Isaac, rep+1.9.7.12. In the app, every number opens the run that produced it.

What’s inside

Encyclopedia: Every collectible, trinket, card, pill, character and boss. Stats, pools, unlock conditions, synergies, folk names. Search by name, alias, colour or a photo of the pedestal.
Quiz and daily puzzle: Bronze to endless, with a fresh puzzle each day. Seasons and leaderboards come later, once the question bank has earned them.
Progress and planner: Track unlocks per platform and save slot, by hand or from Steam. The planner turns “I want every achievement” into “do this run next”.
Assistant: Ask in plain words. It answers only from the codex and links the entry it used, so it cannot invent a synergy that isn’t there.

Free and Pro

Most of the app is free. Pro pays for the lab that produces the data.

Free	Pro
Brief entries for every item and character Search, photo recognition, favourites Daily puzzle, quiz up to silver Progress tracking Comments (read), assistant three times a day	Expert entries with the experiment evidence Synergy and unlock planner Gold, diamond, king and endless quiz, question packs Patch-note explainers Themes, posters, cloud sync, unlimited assistant, screenshot analysis

No ads on either. Ever.

Pro is planned at $2.99 a month, $14.99 a year, or $29.99 once. Final prices at launch.

Why we stopped copying

The game has shown item descriptions since 1.9.7.13, but only for items you have already picked up, only after beating Mom, and only one line. Wikis go deeper, but they are slow on a phone and the numbers are sometimes wrong or out of date.

So the codex is built differently. An automated lab runs each item through the same experiments in the actual game, records the results, and the entry is written from those results only. When the game updates, the lab runs again. If you spot a mistake, the correction goes back to the lab, not to a forum thread.

Be there for the beta

The first testers get in this autumn. We write once when it opens, and never otherwise.