https://gis.stackexchange.com/questions/115433/online-wkt-and-geojson-viewer
Are there any online WKT editors?
geojson.io GeoJSONLint GeoJSON viewer
Wicket OpenStreetMap WKT Playground
I created this little utility for a co-worker to plot multiple WKT or GeoJSON geometries on a Leaflet map. You can fork it and tailor it to your needs. http://jsfiddle.net/asnyder14/9dxbcr4f/embedded/result/
WKT visualizer on 3D Earth https://asapelkin.github.io/wkt_3d_viewer (repo with examples and readme)
In case anyone comes across this question and needs to convert to/from Esri (ArcGIS) json, geoJson, or WKT, I created a small application called geometry-inspector: https://github.com/BrianBunker/geometry-inspector It is much like the listed applications in the accepted answer, but with the improvement that it supports Esri's json format.
http://mapshaper.org/ mapshaper worked well for huge GeoJson file but unfortunately it plots on white background instead of map.
wkt: https://arthur-e.github.io/Wicket/sandbox-gmaps3.html https://clydedacruz.github.io/openstreetmap-wkt-playground/
geojson: http://geojsonlint.com/
csv: https://www.becsv.com/csv-viewer.php
.shapefile/geojson/csv: https://mapshaper.org/ https://www.sunearthtools.com/tools/gps-view.php
svgviewer: https://www.w3schools.com/graphics/tryit.asp?filename=trysvg_path
svg handling: https://github.com/substack/svg-linearize https://github.com/davidmcclure/svg-to-wkt https://www.w3.org/TR/SVG/paths.html https://stackoverflow.com/questions/5736398/how-to-calculate-the-svg-path-for-an-arc-of-a-circle
geojson on leaflet: Adding GeoJSON layer on leaflet?
converters: CSV to GeoJSON: http://csv.togeojson.com/ CSV to GeoJSON: http://www.convertcsv.com/csv-to-geojson.htm JSON to CSV: https://json-csv.com/ JSON to CSV: http://www.convertcsv.com/geojson-to-csv.htm
examples: wkt: https://en.wikipedia.org/wiki/Well-known_text#/media/File:SFA_Polygon.svg csv: https://github.com/naturalatlas/geocsv-info/blob/master/example.csv geojson: https://www.mapbox.com/mapbox-gl-js/example/geojson-polygon/ svg path: https://jsbin.com/quhujowota/1/edit?html,js,output svg path: https://codepen.io/anon/pen/XogNoZ
For bash, I use my own script: https://gist.github.com/rajanski/4d2595c1fd4e35c19b4e1a02b4ed579f Pro: Geojson data doesnt leave local machine, good for confidential stuff.
Github/Gists can handle GeoJSON: https://help.github.com/en/articles/mapping-geojson-files-on-github