NOTICE
This project is abandoned. This tool formed the basis of https://github.com/Project-OSRM/osrm-frontend/tree/gh-pages/debug, the official debug tile viewer for OSRM.
OSRM, as of version 5.0, supports serving of Mapbox Vector Tiles to view the routing graph that's stored in memory.
Tiles can be retrieved from osrm-routed at URLs like this:
http://localhost:5000/tile?tz=12&tx=656&ty=1582
This tool is a simple HTML viewer that uses Mapbox GL JS to make a slippy map to view the tiles in a browser.
Note of warning: as you zoom out, the tiles get bigger and bigger (each tile contains more data). Beyond about zoom 12, tiles are >1MB in size, and will be very slow to display in your browser. Avoid zooming out too far. If you zoom out to Zoom 0, you'll get tiles that are multiple GB in size for a whole planet datafile, and, well, your whole computer will likely freeze up.
You'll probably need to edit index.html and set the URL for osrm-routed, and the initial coordinates/zoom level.