Zapp Data Formats

zappsdata-formats

A core rule of the Zapp philosophy is Zero Lock-In: the user must be able to export their data into open, human-readable formats at any time. Internal storage may be optimized for speed (IndexedDB, Hive, SQLite WASM), but the exit door must be universal.

Below is a categorised reference of open formats a Zapp ecosystem can share, plus when to use each.

General state and structured data

The bread and butter for app state, preferences, and saved configurations.

JSON (.json) — The default for almost everything. Every language and platform parses it. Use for app preferences, flashcard decks, saved configurations, exported records.
CSV / TSV (.csv, .tsv) — Universal tabular format. Anything that’s a table of records (expense tracker exports, habit tracker history, etc.) should export to CSV so users can open it in Excel, Google Sheets, or a Python script.
YAML / TOML (.yaml, .toml) — Human-readable configuration formats, often used for app settings or Markdown frontmatter.

Databases and complex queries

When JSON gets too slow or memory-heavy for large local datasets.

SQLite (.sqlite, .db) — The ultimate local database. With WebAssembly, browsers can now run full SQLite databases entirely client-side. The user can also download the file and query it on their desktop with any SQLite client.
DuckDB — Newer, very fast analytical database that also runs in the browser via WASM. Excellent for Zapps doing heavy data crunching or pivot tables.

A note on internal-only formats: Hive (for Flutter) is fast but binary and Flutter-specific. Use it for performance internally, but always provide a 1-click export to JSON or SQLite for portability.

Knowledge, writing, and documents

For note-taking, blogging, task management.

Markdown (.md) — The standard for text content. Future-proof because even if every app dies, raw Markdown is human-readable.
OPML (.opml) — XML format for outlines. The standard for exporting/importing RSS feed lists, mind maps, and nested hierarchies.
EPUB (.epub) — Open e-book standard. Under the hood it’s a zip of HTML, CSS, and images. Good fit for Zapps that compile reading material.

Location, health, and fitness

For route data, workouts, and physical tracking.

GPX (.gpx) — Universal XML for GPS tracks, routes, and waypoints. Almost any fitness platform reads and writes GPX.
TCX (.tcx) — Training Center XML. Better than GPX for workout data because it natively supports heart rate, cadence, and power. Most fitness apps accept both.
FIT (.fit) — Garmin’s binary format, smaller than TCX but requires a library to read/write. Worth supporting alongside TCX for Strava uploads.
GeoJSON (.geojson) — Geographic features in JSON. Unbeatable for web-map apps because browsers and map libraries parse it instantly.

See Indoor Virtual Run Data Sources for how to source GPX route data for treadmill / smart-trainer apps.

Personal information management

iCalendar (.ics) — Global standard for calendar events. A scheduling Zapp can generate an .ics file that imports straight into Apple Calendar, Google Calendar, or Outlook.
vCard (.vcf) — Standard for electronic business cards and contacts.

Graphics and media

SVG (.svg) — Scalable Vector Graphics. Because it’s text-based XML, a Zapp can generate and manipulate SVGs mathematically without heavy image libraries.

The export-by-default rule

A useful rule to add to any Zapp design checklist:

Internal storage can be optimized. The export must be universal.

If a Zapp uses Hive or IndexedDB internally for performance, it must still expose a 1-click export to JSON (or a more specific open format) so users can move their data elsewhere. A Zapp ecosystem becomes truly useful only when data flows freely between apps — drag the JSON out of one and drop it into another.

A loose mapping of data type to format

Data type	Default format	When to upgrade
App preferences	JSON	TOML if shared with humans
Tabular records	CSV	SQLite for large queryable data
Notes / writing	Markdown	OPML for outlines, EPUB for compiled reads
GPS routes	GPX	TCX/FIT for workouts with biometrics
Calendar events	iCalendar	—
Contacts	vCard	—
Graphics	SVG	—
Configuration	JSON / YAML	TOML for human-edited files