Backup Format

App backup format, version 1

Source of truth: this wiki page.

Settings → Your data → Back up now saves the whole app as one file, fluenough-backup-<yyyy-mm-dd>.fnbackup (#470). Restore from a file reads such a file back.

The file is a plain zip of small UTF-8 text files, so a backup outlives the app the way the review log does: any unzip tool opens it. The app writes its entries stored, not compressed, and reads stored or deflated entries, so a backup unzipped and zipped again by hand still restores. No encryption, no zip64, no multi-disk archives.

A backup never holds deck files, nor anything that restricts a profile. After a restore the languages it lists download again.

Parts

File	What it holds
manifest.json	What the file is; read first. Required.
log.jsonl	The review log, leech actions and fitted parameters, byte for byte the file Export review log writes (Log-Format).
settings.json	Every setting, as a JSON object of string keys to string values, except the reviewer's.
reviewer.json	The reviewer's settings, the same way: review_decks, rater_code (the access code; owner, 2026-10-11), review_intro_shown, reviews.
downloads.json	{"languages": ["bn", "hi"]}: the languages whose decks were on the phone.

A part that is missing reads as empty, and a setting that is not there takes its default. A file or key the app does not know is ignored.

manifest.json

{"format":"fluenough-backup","version":1,"appVersion":"0.5.0","schemaVersion":7,"createdAt":"2026-09-28T13:10:00.000Z","kind":"you","reviews":6,"parts":["log.jsonl","settings.json","reviewer.json","downloads.json"]}

Field	Notes
format	Always fluenough-backup. A file without it is not a backup.
version	The backup format, 1. An app refuses a file whose version is newer than it reads, names the app that made it, and changes nothing.
appVersion	The app version that made it.
schemaVersion	The database schema then. Informational only: every part is read by its own format, never as table rows, so a backup survives migrations.
createdAt	ISO 8601, in UTC.
kind	What made it: you (Back up now), update (an app update began to download), restore (the copy of what a restore replaced), file (a file restored from, kept as it was read). Unknown reads as you.
forVersion	For an update backup, the version being downloaded.
reviews	How many reviews log.jsonl holds, so Recent backups can say without reading the log.
parts	The other files in the zip.

Kept on the phone

The app keeps backups in its own storage, which an update leaves alone: the five newest of any kind, of which at most the three newest made by an update. Each can be downloaded or restored from Recent backups.

Restore

A restore reads and checks the whole file, and shows what it holds, before anything changes. It replaces the progress and settings the learner has, after asking, and keeps a copy of them first. Replacing the append-only review log is the one logged exception to AGENTS.md rule 9 (owner, 2026-10-17: "Logged exception"): in one transaction, the database empties reviews and leech_actions, writes the backup's, and appends to restores when it happened, which backup it was and the name of the copy kept first. A failure leaves the app as it was.

See also: Contributing · Home