# What a codex is, and whether you need one

### The idea

A codex is the bible of your world: the characters, places, things, factions, rules, events and maps, each with a page of its own, and each page knowing what is true *where* and *when*. Write keeps one per universe, so every series set in that world reads from the same book of facts—and so does any AI you've connected, which is where a codex really starts to pay for itself.

If you've ever kept a spreadsheet of eye colours, or scrolled back three books to check which hand a character lost, this is that, kept for you.

### Do you need one?

Not right away, and maybe not at all. A standalone novel with a dozen characters does fine with the notes panel—and notes have tags now, so they can be a small codex of their own (see [Notes that become codex entries](/link/37)). A codex earns its keep when:

- you write a series, or several series in the same world;
- facts change over time—a city falls, a captain is promoted, a name changes—and you need to know what was true *in this book*;
- you want an AI to check your continuity or draft with the world in mind;
- you've lost track of something you invented, and it was important.

Start with notes. When a note wants to be shared across books, turn it into an entry; the rest of the codex can grow from there.

### How it's put together

- A **universe** is the world. It belongs to a pen name, and series join it. One universe, one codex.
- An **entry** is one thing in the world: *Tanis Richards*, *the Intrepid*, *Transcend*. Every entry has a type—character, place, item, faction, rule, event, map, or one you've added yourself.
- Each entry has a **summary** (one line), a **body** (as much as you like), and **at-a-glance information**: the fields on the right-hand side of its page, like the box on a Wikipedia article. Fields can hold general information, or information that applies only to one book, one series, or a stretch of time.
- **Calendars** let a fact have a *when*. The codex starts with an ordinary Gregorian calendar; a science-fiction universe can add its own, with its own way of writing dates.
- **Mentions** search your books for an entry's name and aliases, so you can see every scene a character walks through.

### Where to find it

From the Library, **Manage → Codexes** lists your universes, each with an **Open codex** button. From inside a book, the **Codex** button in the editor's toolbar opens a rail that shows who and what the scene you're writing mentions, with a link to the whole codex framed to that book—see [The codex while you write](/link/32).