Paste geometry in one format, get the others — plus vertex count, bounding box, geodesic length, and area. All parsing and math runs locally; nothing leaves this page. Input persists in this browser via localStorage.
Use limits: Coordinates are assumed to be WGS84 lon/lat degrees (the GeoJSON spec's only CRS, and what OSM and GPS produce). Lengths and areas are spherical-earth geodesic values (mean radius 6,371,008.8 m) — within about 0.3% of rigorous ellipsoidal values, plenty for inspection and QA, not for legal areas or record boundaries. First supported geometry only: FeatureCollections are read, but the tool inspects the first feature's geometry and says so.
Inspection
Detected input / geometry
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Vertices
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Bounding box (W, S, E, N)
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Geodesic length
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Geodesic area
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GeoJSON
WKT
CSV (lon,lat vertices)
How the Numbers Are Derived
Length and area math
Length: haversine great-circle distance summed over consecutive vertices, R = 6,371,008.8 m (IUGG mean radius). Area: the spherical polygon formula (sum of (λ₂−λ₁)·(2 + sin φ₁ + sin φ₂) over ring edges, times R²/2), holes subtracted — the same approach most GIS "geodesic area" functions use on a sphere. Both are within ~0.3% of ellipsoidal values at mid-latitudes; for record areas, compute on the ellipsoid in real GIS software.
What the parsers accept
GeoJSON: a bare geometry, a Feature, or a FeatureCollection (first geometry used, with a note). Point, MultiPoint, LineString, MultiLineString, Polygon, MultiPolygon. A legacy crs member triggers a warning — modern GeoJSON is WGS84 by definition.
WKT: the same seven types, case-insensitive, tolerant of whitespace. No Z/M coordinates, no EWKT SRID prefixes.
CSV: one coordinate pair per line, comma / tab / whitespace separated, header row auto-skipped if non-numeric. You choose column order and whether the rows are a path, a polygon (auto-closed), or loose points.
The lat/lon swap check
The most common geometry bug in existence is swapped axes. The tool flags input where a "longitude" magnitude never exceeds 90 while a "latitude" does — the signature of lat,lon data read as lon,lat. GeoJSON and WKT are lon-first by spec; most spreadsheets and GPS apps are lat-first by habit. Everyone gets bitten eventually.
References
RFC 7946 — The GeoJSON Format. https://datatracker.ietf.org/doc/html/rfc7946
OGC Simple Features — WKT specification. https://www.ogc.org/standards/sfa
Chamberlain & Duquette (JPL), Some Algorithms for Polygons on a Sphere — spherical area formula.