Every format needs a referee, and for the Gerber format the referee has a name: Ucamco, the company that maintains the Gerber specification, publishes the Reference Gerber Viewer — its online reference implementation of the format. Gerbv is something else: a free, open-source desktop viewer (GPL-2.0-or-later) for Windows, macOS and Linux that you install once and use offline for everyday inspection. Comparing them is not about crowning a better renderer. It is about two different purposes — defining what correct means, and doing daily work — and knowing which tool to open for which question. Both sit in our best free Gerber viewers roundup, and the general case for a desktop viewer is made in online vs desktop Gerber viewers.
What a reference implementation is for
When two programs render the same Gerber file differently, someone has to be right. The reference viewer’s rendering is that arbitration: it shows the file as the specification’s maintainer intends it to be understood. That makes it the natural destination for a narrow, important class of problems — “this file looks wrong in my viewer; is the file odd, or is the viewer?” If the reference viewer shows the same oddity, the file is the story and you go back to the exporter. If it renders cleanly, you have learned something about your everyday tool, and you have a concrete, reproducible case to report. No ordinary viewer, Gerbv included, can claim that authority; a reference implementation does not need features to justify itself.
What the everyday tool is for
Daily inspection is a different sport: a full fabrication set, checked layer by layer, against a deadline. That is Gerbv’s design centre. It stacks Gerber RS-274X layers, Excellon drill files and CSV pick-and-place files together, so drills can be checked against pads and silkscreen against copper. It measures distances on the displayed image, opens report windows with statistics on the Gerber and drill codes used — including aperture usage — and exports the view to PNG, PDF, PS, SVG and DXF for documentation and fab correspondence. It runs on your machine, offline, with no upload and no account, which keeps client designs under your own confidentiality rules. Get it from the download page; the working routine is laid out on the Gerber viewer hub.
Online reference vs offline desktop in practice
The reference viewer lives online, in the browser: nothing to install, ideal for the occasional arbitration visit, and — like every online tool — somewhere your files travel to be rendered, which you should weigh for confidential work. Gerbv lives on your disk: available on a plane, in a restricted lab, or on the factory network that never touches the internet, and the same on every visit. There is also a consistency argument for daily work: checking revision twelve in the same tool, with the same habits and checklists as revisions one through eleven, catches differences that hopping between tools would mask.
Gerbv’s limits, for the record
Gerbv is a 2D viewer. It performs no DRC or DFM validation — its reports are statistics for your judgement, not verdicts — and it does not read legacy RS-274D files. And in the specific matter of spec interpretation, Gerbv is a participant, not the referee: its reading of RS-274X is its own implementation, which is precisely why the reference viewer exists as a court of appeal when an edge case matters.
A worked example of using both
Picture the situation the pairing exists for. A board comes back from a colleague and one layer renders in Gerbv with a shape you did not expect — a region that looks filled in your design intent appearing as an outline, say. Step one is local: check the layer stack, the file’s companions and your assumptions in Gerbv, where the full set is already loaded. If the oddity survives, step two is arbitration: load that single file in the reference viewer. Same shape there means the file genuinely says that, and the fix belongs in the export. A clean render there means the interpretation differs, and you have isolated a viewer edge case with evidence in hand. Ten minutes, two tools, no guessing — and the everyday nine cases out of ten never leave your desktop at all.
Verdict: workhorse and referee
Choose Gerbv for the everyday job — full sets, measurement, reports, export, offline and private. Choose the Ucamco Reference Gerber Viewer when the question is about the format itself: a rendering dispute, a strange construct in a file, a case where “what does the specification’s own viewer do with this?” is the deciding evidence. Keep both in the toolbox; they are answers to different questions that happen to share a file format.
Frequently asked questions
What is the Ucamco Reference Gerber Viewer?
It is the online reference implementation published by Ucamco, the maintainer of the Gerber specification. Its rendering shows how the format is intended to be interpreted, which makes it the authority to consult when viewers disagree about a file.
Can Gerbv replace the reference viewer?
For everyday inspection, yes — stacking layers, measuring, reporting and exporting are Gerbv’s job, done offline on your machine. For arbitrating how a disputed construct should render, no ordinary viewer replaces the reference implementation; that is what it is for.
Which should I use for confidential designs?
Gerbv, as the default: it runs entirely on your machine with no upload, so the design stays under your control. Reserve the online reference viewer for the occasional spec question, ideally with a minimal test file rather than a full confidential design.