Gerber Viewer
View PCB fabrication files right in your browser. Drop a Gerber set (RS-274X) and an Excellon drill file — or a whole .zip — and Gerber Viewer parses and renders the board: copper traces and pads, soldermask, silkscreen and drill hits, composited with pan, zoom, per-layer toggles and a top/bottom flip. It auto-detects each layer, reports the board size, layer count and hole count, and lets you measure distances. Everything runs locally — nothing is uploaded.
How to Use
- Drop your <strong>Gerber files</strong> (<code>.gbr .ger .gtl .gbl .gts .gto .gko …</code>) and the <strong>Excellon drill</strong> file (<code>.drl</code>) onto the drop zone — or drop a single <strong>.zip</strong> of the whole fab package and it unpacks it for you. You can also click the zone to browse.
- Gerber Viewer <strong>auto-detects each layer</strong> — top/bottom copper, soldermask, silkscreen, board outline and drill — from the Gerber X2 file attributes or the filename, and renders them composited into a board view.
- Use the mouse <strong>wheel to zoom</strong> and <strong>drag to pan</strong>. Toggle individual layers on the right, hit <strong>Fit</strong> to recenter, and <strong>View: Top/Bottom</strong> to flip the board over.
- Turn on <strong>Measure</strong> and click two points to read the distance in millimetres. The <strong>board stats</strong> panel shows the dimensions, layer count, drill-hit count and unique drill sizes.
- No files handy? Click <strong>Load sample board</strong> to see a small demo PCB render immediately.
What it renders
How Gerber files work
A PCB is manufactured from a set of Gerber files — one per physical layer — plus an Excellon drill file. Each Gerber file (RS-274X, plain ASCII) declares a coordinate format and units, defines a table of apertures (the shapes of pads and the widths of traces), then issues draw (D01), move (D02) and flash (D03) operations that paint copper, soldermask or silkscreen. Gerber Viewer parses all of that into geometric primitives and composites the layers, so what you see is exactly what the board house will make.
The PCB toolset
Gerber Viewer sits alongside the rest of the Utilities Bunker electronics tooling — check your fab files here, then jump to the calculators for the numbers behind them.
About the Gerber Viewer
The Gerber Viewer gives you a fast, free answer for electronics and circuit design without sending anything off your device. View PCB fabrication files right in your browser. Drop a Gerber set (RS-274X) and an Excellon drill file — or a whole .zip — and Gerber Viewer parses and renders the board: copper traces and pads, soldermask, silkscreen and drill hits, composited with pan, zoom, per-layer toggles and a top/bottom flip. It auto-detects each layer, reports the board size, layer count and hole count, and lets you measure distances. Everything runs locally — nothing is uploaded.
How it works
Type in what you have, and the answer shows up right away. Change anything and it updates by itself. Everything runs in your browser, so it is fast and nothing you type is sent away.
Want the deeper story? The Knowledge Base explains the ideas behind the tools in more detail.
Frequently Asked Questions
What files does it accept?
Modern <strong>RS-274X Gerber</strong> files (the extended format every current PCB tool exports) and <strong>Excellon</strong> drill files. Drop them individually or as a <code>.zip</code> fab package. It reads the common naming schemes from KiCad (<code>-F.Cu</code>, <code>-B.Mask</code>, <code>-Edge.Cuts</code>), Altium/Protel/Eagle (<code>.GTL .GBL .GTS .GTO .GKO</code>) and others, and prefers the Gerber X2 <code>%TF.FileFunction%</code> attribute when it's present.
Is anything uploaded to a server?
No. The Gerber and Excellon parsers, the layer compositing and the renderer all run in your browser with JavaScript and a <code><canvas></code>. Your design files never leave your computer, and it works offline.
How accurate is the render?
It draws the real geometry from the files — traces (with the correct aperture width and round/square caps), flashed pads (circle, rectangle, obround and polygon apertures), filled copper regions, arcs, and drill hits — scaled from the file's format and units. It's a faithful 2-D fabrication preview, not a 3-D board render.
What are the current limitations?
This is a v1 viewer. <strong>Custom aperture macros</strong> (<code>%AM</code>) are approximated by their bounding circle and flagged in the notes rather than drawn primitive-by-primitive; <strong>step-and-repeat</strong> panels render the first instance; and it targets modern RS-274X, not the legacy RS-274D format with separate aperture files. Anything it can't fully interpret is noted in the <em>Notes & assumptions</em> panel rather than silently mis-drawn.
Does it check my board against fab rules?
Not yet. Design-rule checking (minimum trace width, clearance and annular ring against a JLCPCB / PCBWay preset) is planned for a later version. For now use the board stats and the dedicated <a href="https://utilitiesbunker.com/tools/pcb-trace-width">PCB trace-width</a> and <a href="https://utilitiesbunker.com/tools/microstrip-impedance">impedance</a> calculators.
Why can't I see a layer?
Check that it's toggled on in the Layers panel, and that the file was recognised — anything it couldn't classify is listed as <em>Unknown</em> (still rendered) or noted in the assumptions panel. Soldermask layers are drawn semi-transparent by design so the copper shows through, and clear-polarity regions are knocked out.
How do I use the Gerber Viewer?
Just type your numbers. The answer shows up right away — there is no button to press. Change anything and it updates by itself.
Does it cost anything or need an account?
No. The tool is completely free, there is no account to create, and it keeps working offline after the page first loads.
Is anything I type uploaded?
No. The tool works entirely on your device, so the values you enter never leave your browser.
Common Use Cases
Check fab files before ordering
Sanity-check the Gerbers your tool exported before you send them to a board house.
Open a Gerber .zip
Someone sent you a fab package — see what's inside without installing anything.
Verify layer alignment
Toggle copper, mask, silk and drill to confirm pads, holes and silkscreen line up.
Read a board's dimensions
Get the board size, layer count and hole count straight from the files.
Measure features
Click two points to measure spacing, hole pitch or board edges in millimetres.
Learn the Gerber format
See how apertures, draws, flashes and regions become a real PCB.
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