Which one lets you actually fix a toolpath, and which ones are built for a different job entirely.
These four tools all open a .tap or G-code file in your browser, and that's about where the similarity ends. Three of them are viewers and simulators — you load a file and watch what your machine is about to do. One of them, TestTalkHQ's own, is built to edit that file: click an individual toolpath, move it, rotate it, or delete it, without touching the rest of the program. None of these is "better" across the board. They solve different problems. Here's what each one is actually for.
If you want the practical walkthrough rather than the feature comparison, start with how to edit, nest, and fix a TAP/G-code file without going back to CAM.
If the editor loads but results look wrong — parse alerts, bad nests, out-of-bounds selection, or clip surprises — use TAP File Editor Troubleshooting.
NCViewer — 3D Simulation and Playback
NCViewer is a full-featured backplotter: 3D toolpath view, a live digital readout for X/Y/Z and rotary A/B/C axes, plot orientation switching (vertical Z-up or horizontal Y-up), lathe diameter mode, and 5-axis movement support. Settings for showing rapid moves, toolpath points, and hiding the toolpath after the current position make it a genuinely capable simulator for checking a program before it runs.
What it doesn't do: edit. There's no way to select a single toolpath and move it — NCViewer shows you what the file will do, it doesn't let you change what the file does.
CutViewer — Large-File 3D Viewing
CutViewer is a browser-based G-code viewer built around handling big files — it explicitly advertises support for files with millions of lines, plus real-time 3D rendering and animation that plays the cut in the order it'll actually run. It confirms support for the core G-code moves that matter for verification: rapid moves (G00), linear interpolation (G01), circular arcs (G02/G03), plane selection, inch/metric units, absolute/incremental positioning, and work coordinate systems G54–G59.
CutViewer does include a built-in G-code editor with syntax highlighting and line-level navigation — you can jump to any point in the toolpath and edit coordinates or feed rates directly, with the 3D view updating live. What it doesn't do is let you select one toolpath and move it independently of the rest of the program — its editing is text-level, line by line, not a select-and-drag operation on a specific cut.
G54.APP — The Closest Comparison, and Where It Actually Differs
G54.APP deserves the most careful treatment here, because it's the one tool in this list that does real editing, not just viewing. Its "Hack panel" can translate, rotate, flip, swap tools, and remap feedrates on a loaded program, and it pairs that with a genuinely strong simulator: 60+ fps real-time playback, stock-removal simulation with correct geometry for flat, ball, bullnose, taper, and V-bit tools, a customizable tool library, a built-in G-code editor with syntax highlighting and autocomplete, and a work-offset (G54) origin picker covering all 27 anchor positions on rectangular stock. It also has a share-by-link feature (uploads deleted automatically after 30 days) and offline desktop builds for Mac and Windows.
Here's the distinction that actually matters: G54.APP's Hack panel transforms operate on the whole loaded program at once. Translate, rotate, or flip, and every toolpath in the file moves together. There's no way to select one toolpath in the middle of the file and move just that one while the rest of the program stays put. If your problem is "shift the entire job two inches because you clamped the stock differently," G54.APP handles that well. If your problem is "this one part needs to move, the rest is fine," it doesn't have a tool for that.
TestTalkHQ's TAP File Editor — Per-Toolpath Editing
This is the piece none of the above three cover: click an individual toolpath and it highlights, drag it or Alt+drag to rotate it around its own center, nudge it with arrow keys, delete it outright, undo any of it. Board-size checking (does it fit your material) and machine-limit checking (will it crash the machine) run as two separate systems with distinct warning colors, plus an auto-select for anything out of bounds and a one-click clip to bring it back inside your machine's travel. Bit-diameter kerf is shown to scale so you can eyeball real clearance, not just a line.
It's a 2D, top-down editor — no 3D stock-removal simulation, no playback animation. That's a real tradeoff, not an oversight: the tool is built for repositioning and cleanup, not for verifying complex multi-axis programs the way NCViewer or CutViewer do. One honest limitation worth naming: arcs (G2/G3) are read by their endpoints and displayed as straight segments between points, not as true curved arcs — fine for repositioning and nesting, but not a substitute for a full 3D arc-aware simulator if you need to visually verify complex curved toolpaths before running them.
Comparison Table
| NCViewer | CutViewer | G54.APP | TestTalkHQ TAP Editor | |
|---|---|---|---|---|
| 3D view | Yes | Yes | Yes | No (2D top-down) |
| Per-toolpath selection | No | No | No | Yes |
| Drag/rotate a single toolpath | No | No | No | Yes |
| Whole-program transform (translate/rotate/flip/tool swap) | No | Line-level text editing, not select-and-move | Yes | No — by design, edits are per-toolpath, not whole-file |
| Board-fit (material size) check | Not confirmed | Not confirmed | Not confirmed | Yes |
| Machine-limit (crash) check | Not confirmed | Not confirmed | Not confirmed | Yes |
| Stock-removal simulation | Not confirmed | Not confirmed | Yes | No |
| Kerf/bit-width shown to scale | Not confirmed | Not confirmed | Yes (via stock-removal sim) | Yes |
| Arc (G2/G3) handling | Not confirmed | Yes, rendered as true arcs | Not confirmed | Reads arc endpoints; displays as straight segments |
| Dark/light mode | Not confirmed | Not confirmed | Yes (dark default) | Yes |
| Runs fully in-browser, no upload | Not confirmed | Not confirmed | No — file-sharing feature uploads to their servers (auto-deleted after 30 days) | Yes — nothing leaves the page |
| Desktop app option | Not confirmed | Not confirmed | Yes (Mac/Windows, offline) | No — browser only |
| Cost | Free | Free | Free | Free |
Rows marked "not confirmed" aren't a knock against those tools — we didn't find explicit documentation either way, and we'd rather say that than guess.
Which One Do You Actually Need
Verifying a large, complex program before it runs, especially multi-axis or lathe work → NCViewer or CutViewer. Both are built for viewing and simulating, and CutViewer in particular is built to handle very large files without choking.
Shifting or rotating an entire job at once, swapping a tool, or remapping feedrates across the whole program → G54.APP. Its Hack panel is a real, useful whole-program editor, and its stock-removal simulation is a genuine step up if you want to see material actually disappear as the tool cuts.
Fixing, nesting, or cleaning up individual toolpaths after CAM — moving one part, rotating one cutout, deleting one bad cut — without a full recompute → that's the gap TestTalkHQ's TAP File Editor is built for. If the fix you need is smaller than "redo the whole program" and bigger than "shift everything the same way," this is the one built for that specific job.
Built for the Shop Floor