OSMPR

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Preview proposed changes to OpenStreetMap.

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Comment (editable before upload):

Link format

Primary format — one URL parameter d with base64url-encoded JSON (UTF-8). No full geometry, no full member lists: only the operations. The page fetches current objects from the OSM API and applies them.

{
  "comment": "Changeset comment",
  "changes": [
    {
      "type": "relation", "id": 175342, "version": 217,
      "add":    [{ "type": "relation", "id": 51805, "role": "subarea" }],
      "remove": [{ "type": "relation", "id": 51805, "role": "subarea" }],
      "tags":   { "name": "New name", "old_key": null }
    }
  ]
}

version is optional. If present and the live version differs, upload is blocked until you click Rebase (refetch + re-apply).
add entries already present (same type + id + role) are skipped with a note; remove entries not present produce a warning. Neither is fatal.
remove without a role matches any role for that type + id. tags value null deletes the tag.
Member operations only apply to relations. Tag operations apply to nodes, ways, and relations.
Geometry: a node change may set lat and lon (both, decimal degrees); a way change may set nodes (array of node ids). The Map view draws the object and highlights old vs new geometry; Diff shows them in a Geometry section.
New objects: use a negative id (e.g. -1) in a change. The object is created on upload, and other changes can reference it by that id — list created objects before the changes that reference them.
Delete an object: set "delete": true in a change. Upload sends DELETE after creates and modifies; the object must not be used by another object, or the server refuses (412). Other operations in the same change are ignored.
Map view shows the object on OpenStreetMap tiles (Leaflet, loaded from CDN the first time Map is opened).
Upload is disabled when every computed object is unchanged (so re-opening an already-applied link cannot re-upload it).
View an existing changeset the same way: ?changeset=1234567, or paste an id/URL in the page header. After a successful upload the page switches to the new changeset's view automatically.

Simple format for a single relation (no JSON): ?rel=175342&v=217&add=rel:51805:subarea&comment=… — add/del may repeat; member spec is type:id[:role] with type n/w/r or node/way/relation. If both d and rel are present, d wins.