What Is a Story Bible
A story bible is the reference document for what's already been established inside a novel: character names and ages, dates, geography, family relationships, which details have already been given to the reader and which haven't. It exists so a writer doesn't have to hold every fixed fact in memory across a long manuscript, and so a later chapter doesn't quietly contradict an earlier one about something as simple as a character's eye color or how many siblings they have.
Where the confusion comes from
A story bible gets mixed up with research notes, and the two look similar on the page: both are collections of facts sitting outside the manuscript. The difference is what kind of fact each one holds. Research notes describe the world before the writing starts, sources and background a writer might or might not use. A story bible describes only what the novel itself has already committed to, on the page, as true within its own story. One is raw material. The other is a record of promises already made to the reader.
How this shows up in a real novel
Jane Austen's Persuasion (1817) depends on a set of established facts holding steady across the whole book: Anne Elliot's exact age, the eight years since she broke her engagement to Captain Wentworth, the precise social rank of every family that enters a room. Austen's novels are known for this kind of internal consistency, ages and timelines that stay accurate from one chapter to the next, which is exactly the job a story bible exists to protect once a manuscript gets too long to hold in memory alone.
While you're drafting
A story bible earns its keep less at the start of a project than in the second half, once there are enough established facts that keeping them straight from memory stops being realistic.
Questions
Is a story bible the same as research notes? No. Research notes are background material gathered before or during writing. A story bible only records what the novel has already stated as true within its own pages.
Do short novels need a story bible? Not always. It becomes useful once there are enough characters, dates, or locations that a writer can no longer be certain of every detail from memory alone.
When should a story bible get started? Whenever the risk of contradiction starts to feel real, which is often earlier than expected: a single named minor character can be enough to justify starting one.