Guide · Bring your data with you

No history left behind.

Switching to HackDiet from another tracker — v1.0 status

Years of weigh-ins are too valuable to leave behind. HackDiet ships with one rock-solid import path and a forgiving CSV detector that catches most of the rest. If your tracker isn't covered, email us a sample export — we'll see what we can do.

The rock-solid path: Hacker's Diet XML

HackDiet's native format is the same XML the Hacker's Diet Online tool has used since 2003. Round-trips bit-for-bit: import the file, export it again, the two are identical except for the export timestamp. Trend, weights, comments, flags, units, plan settings — all preserved. If you've been logging there for years, this is the smoothest move you'll ever do.

Step 1 — Export from the Hacker's Diet Online

Sign in at fourmilab.ch/cgi-bin/HackDiet.
Open Utilities › Export.
Choose Hacker's Diet Online XML, Export all months, click Export.
Save the file somewhere your iPhone can reach it — iCloud Drive, Files, or email-to-self.

Step 2 — Import into HackDiet

Open HackDiet on your iPhone.
Tap Settings › Data › Import data.
Pick the XML file. The importer detects the format and shows you a preview before committing.
Done. Trend redraws, stats recompute, plan history is preserved.

Auto-detected formats

The same import sheet auto-detects 6 source formats — drop in the file, HackDiet figures out which it is. No "pick which app this came from" question, no per-format configuration:

Apple Health — the export.zip from Health → Profile → Export All Health Data. Body-mass samples only.
Hacker's Diet (XML) — the fourmilab format described above; full round-trip.
Libra — the Android trend-weight tracker. Use its CSV export.
MyFitnessPal — the CSV export from the website (Premium-only at the time of writing — outside HackDiet's control).
Withings — the CSV from the Withings data-export tool.
CSV — heuristic fallback for any other CSV with a date column and a weight-shaped numeric column. Body-composition columns (fat / muscle / lean / BMI / etc.) are rejected by header keyword so they can't be misread as weights.

Tracker not on the list?

Many trackers export CSVs whose shape happens to match the heuristic above — date column, weight column, sane numeric range — and those will import just fine even though we haven't fingerprinted them explicitly. So the first thing to try is just running your file through the importer.

If it doesn't catch your file, email us with the export attached. We'll look at it. If the format is clean and the data is reachable, we'll add detection in a future update — and you'll be the one to thank for it. We won't add an importer until we've validated a clean round-trip against real data, so promising day-one support for every CSV dialect on a roadmap is something we deliberately don't do.

We're not offering a manual conversion service — single-developer shop, doesn't scale. But the email path above is short and direct, and your sample is what unlocks the format for everyone else who'd benefit.

What round-trips, what doesn't

For the supported formats, every weight survives, in the unit you logged it. The fourmilab XML round-trip additionally preserves comments, flags, "rung" exercise values, and the active plan. CSV imports carry the date and the weight; anything else in the file is ignored.

Going back the other way: Settings › Data › Export Data (XML) writes a fourmilab-compatible file you can upload anywhere — including back to the Hacker's Diet Online itself. Door swings both ways. Your data is yours.