The Vertices link tool renders handles above all vertices of the link. It accepts three additional arguments, which can be passed as an object to the link tool constructor:

redundancyRemoval boolean If the user arranges three (or more) vertices so that they lie on a single line, should the middle one(s) be considered redundant and removed? Default is true. Note that this setting is not applied until the user actually moves one of the vertices in question; this means that vertices can still be arranged in this redundant fashion, using of the link.vertices function, for example.
snapRadius number While the user is moving the vertex, from how far away should the vertex snap in order to arrange itself perpendicularly to another vertex? Default is 20.
vertexAdding boolean Can the user add new vertices (by clicking a segment of the link)? Default is true.
stopPropagation boolean Should be events stopped from propagating to the paper? Default is true.

Example:

var verticesTool = new joint.linkTools.Vertices({
    focusOpacity: 0.5,
    redundancyRemoval: false,
    snapRadius: 10,
    vertexAdding: false,
});