One extension, three different files.

A waypoint file is the simplest thing in free flight: a list of named places with coordinates and an elevation. It is also the least standardised. Three lineages produce files called .wpt, and none of them declares which it is in a way you can rely on:

A fourth thing you will meet is $FormatUTM — the same FS file with UTM grid coordinates instead of latitude and longitude. It cannot be read without knowing the grid zone, and it is not worth guessing: reject it and ask for a GEO export.

The check that works, in order — first match wins:

• Starts with $FormatGEO → FS / GpsDump.
• Starts with $Format anything else (i.e. $FormatUTM) → reject, ask for a GEO export.
• Starts with OziExplorer → OziExplorer.
• Has a G  WGS 84 datum line, or any W <code> A <lat> <lon> record → CompeGPS.
• Otherwise: contains a comma → OziExplorer, else CompeGPS. Headerless Ozi exports are common; commas are the tell.

OziExplorer Waypoint File Version 1.1
WGS 84
Reserved 2
Reserved 3
1,B02 Aujour,44.285000,5.740000,,0,1,3,0,65535,Aujour ridge,0,0,0,6017,6,0,17
2,B15 Hongrie,44.362000,5.715000,,0,1,3,0,65535,,0,0,0,-777,6,0,17

Four header lines, then one row per waypoint with 18 comma-separated columns. Most of them are display settings for OziExplorer's own map view and carry nothing you want.

Rows are CRLF-terminated in files written by Ozi itself. Be tolerant on input, and emit CRLF on output for the benefit of the older tools that still read these.

G  WGS 84
U  1
W  Z20133 A 44.4102700000ºN 6.3516500000ºE 27-MAR-62 00:00:00 1329.000000 Chairlift
W  B02 A 44.2850000000ºN 5.7400000000ºE 01-JAN-70 00:00:00 1834.000000 Aujour ridge

Inside a W record

Latitude can also appear as colon-separated DMS (44:24:36.97N). Accept both: split on :, and treat a single component as plain degrees.

$FormatGEO
Z20133    N 44 24 36.97    E 06 21 05.94    1329  Chairlift
B02       N 44 17 06.00    E 05 44 24.00    1834  Aujour ridge

This is the format competition organisers hand out, because it is what GpsDump writes and what every comp instrument eats. One header line, then one record per waypoint:

Competition waypoints carry a short code (B61130, D01188, A03091) next to a human-readable name. Instruments and task boards key on the code; pilots read the name. Both must survive a round trip.

CompeGPS and $FormatGEO have a natural home for each: the identifier column takes the code, the trailing free text takes the name. OziExplorer does not — like GPX and KML, it has only two text slots, name and description. The convention comp tools settled on:

Recovering the split on import

Promote the primary slot to a code when it looks like one — and the test has to be tight enough not to eat ordinary short names. A competition code is 2–8 alphanumeric characters containing at least one digit:

/^(?=[A-Za-z0-9]*\d)[A-Za-z0-9]{2,8}$/

The digit requirement is what makes it safe. Without it, Goal, Home and Top all become codes and their real names vanish into a field nothing displays.

The promotion applies only when the secondary slot is non-empty and different from the primary. A waypoint with a code-looking name and no description is just a waypoint with a terse name — leave it alone.

Search by field or meaning, or narrow to one dialect. Fields marked shared behave the same way everywhere.

The dialect is sniffed from the content, then every line is decoded. Coordinates are converted to signed decimal degrees and elevations to metres. Nothing is uploaded.

• Ozi altitudes are feet. The other two dialects are metres. Convert, and honour -777 / -9999 as "unknown" rather than as a depth.
• The degree sign is unreliable. Match around it, not on it.
• Encoding is Windows-1252 as often as UTF-8. Accented place names are single high bytes; strict UTF-8 decoding turns them into replacement characters. Try UTF-8 first, fall back to Windows-1252.
• Ozi has no quoting. A comma in a name is unrepresentable. Replace it on export; do not emit a quoted field that no Ozi reader understands.
• $FormatUTM is a different coordinate system, not a variation. Refuse it with a message that says so.
• Line endings are CRLF in files from the original tools. Split on /\r?\n/, write CRLF back.
• Skip unparseable lines, don't fail the file. Headers, comments, blank lines and the occasional truncated row are all normal. Only an empty result is an error.
• Validate coordinates. A mis-sniffed dialect happily produces latitude 4400 or longitude 574. Bound-check every point before you keep it.

The XC planner's waypoint collections import and export all three dialects. Everything is parsed in the browser — an imported collection is only stored when you explicitly save it.

All three export back to .wpt — the extension carries no information, so the dialect is the pilot's choice at download time. Competition codes survive a full import → save → export round trip in every dialect, including through the two-slot Ozi form.

The same collections also round-trip through GPX, KML and SeeYou .cup.