CutViewer vs NCViewer
Two free online G-code viewers, compared honestly — including where NCViewer is the better choice.
NCViewer is the best-known free online G-code viewer, and a good one. CutViewer is a newer free viewer built around one question: is this program safe to run? Both open your file in the browser, draw the toolpath in 3D, simulate it and let you edit the code. The differences are in what they tell you about the program, and in which machines they cover.
The short version
- Use CutViewer for 3-axis routers and mills when you want to check a program before cutting: estimated run time, part size and extents, the tools used, and warnings for problems like a missing feed rate or a rapid move below Z0.
- Use NCViewer for 4th- and 5-axis programs, lathe work, or when you need to view files offline.
Feature comparison
| Feature | CutViewer | NCViewer |
|---|---|---|
| Viewing and simulation | ||
| 3D toolpath view | Yes | Yes |
| Play, pause and speed control | Yes | Yes |
| Click the toolpath to jump to its line | Yes | Yes |
| Arcs (G2/G3 with I/J/K or R, XY/XZ/YZ planes) | Yes | Yes |
| Drilling cycles drawn (G81–G89, G98/G99) | Yes | — |
| 4th / 5th axis (A, B, C) | No | Yes |
| Lathe diameter mode | No | Yes |
| 3D mouse (3Dconnexion) | No | Yes |
| Dark theme for the whole app | Yes | No |
| Checking the program | ||
| Estimated run time | Yes | No |
| Part size and X/Y/Z extents | Yes | No |
| Cutting and rapid distance, feed and spindle ranges, tools used | Yes | No |
| Pre-flight checks (missing feed rate, arcs that don't close, cutting with the spindle off, rapids below Z0, missing units) | Yes | No |
| Editing and files | ||
| G-code editor with syntax highlighting | Yes | Yes |
| Save the edited file | Yes | Yes |
| Open a file from a link | Yes (from supported sites) | No |
| Works offline / installable app | No | Yes |
| Cost and privacy | ||
| Free, no account, no ads | Yes | Yes |
| Files you open stay in your browser | Yes | Yes |
| Free CNC calculators and G-code reference | Yes | No |
Compared in October 2026 against NCViewer v1.2.0. “—” means we couldn't confirm either way. If something here is wrong or out of date, let us know and we'll fix it.
What CutViewer adds: checking before you cut
Seeing the toolpath is only half the job. The other half is catching the mistakes that break tools or ruin stock. When you open a file, CutViewer's Job panel shows:
- Estimated run time, from each move's feed rate (rapids at a typical machine speed).
- Part size and extents of the cutting moves, so you can confirm the job fits your stock and your machine.
- Cutting and rapid distance, feed and spindle ranges, and the tools used.
- Pre-flight checks that list each problem with links to the lines that cause it, and mark those lines in the editor:
- a feed move with no feed rate set
- an arc whose end point isn't on the arc (the same tolerance GRBL uses)
- a cutting move with the spindle off
- a rapid move below Z0 (assuming Z0 is the top of the stock)
- no G20/G21 units before the first move
Where NCViewer is ahead
If you run a 4th-axis rotary, a 5-axis machine or a lathe, NCViewer is the better tool today: it simulates 5-axis files and has a lathe diameter mode, and CutViewer only draws X, Y and Z. NCViewer can also be installed and used offline, and it supports 3D mice.
Try CutViewer
CutViewer is free and runs in your browser. Drop a file in and the Job panel tells you how long it will take and whether anything looks wrong.
Frequently Asked Questions
Is CutViewer an NCViewer alternative?
Yes. Both are free, browser-based G-code viewers that open .nc, .gcode and .tap files, show the toolpath in 3D, simulate it and let you edit the code. CutViewer adds job stats and pre-flight checks; NCViewer supports 5-axis programs and offline use.
Which is better for 3-axis CNC routers like the Shapeoko?
For 3-axis routers and mills, CutViewer's estimated run time, part size and pre-flight checks (missing feed rate, bad arcs, cutting with the spindle off, rapids below Z0) help you catch problems before you cut. Both viewers display 3-axis programs well.
Which one handles 4th-axis and 5-axis programs?
NCViewer. It can view and simulate 3- and 5-axis files. CutViewer currently draws the X, Y and Z axes only and ignores rotary axes (A, B, C).
Do either of them upload my G-code?
No. Both read the files you open in your browser. CutViewer only fetches a file from a server when you open a link to a file hosted online.
Are both free?
Yes. Neither requires an account, and neither shows ads.