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Gerber files are the industry standard for printed-circuit-board manufacturing. Reading one normally requires a desktop CAD package. Loft has a Gerber viewer that runs in any phone browser. Here is how, what it took, and what the limits are.
A board designer emailed me one Friday afternoon. I’m in a fabrication review on an iPad, my vendor just sent me a Gerber bundle, and there’s no Gerber viewer for iPad that I trust with the file. Is your tool ready?
It wasn’t. Six weeks later it was. This post is the postmortem on how a Gerber viewer ended up working in any phone browser in 2026.
Gerber X2 is the standard manufacturing format for printed- circuit boards. A complete board ships as a bundle: one Gerber file per copper layer, an Excellon drill file, layer-pair metadata, an aperture macro definition. Reading the bundle normally requires a desktop CAD package — Altium Viewer, CAM350, GC-Prevue, KiCad. Each of those is Windows-first; the Mac and iPad options are thin or unmaintained.
The designer who emailed me was on iPad because they’d just walked away from their desk and needed to look at the file now. The vendor was expecting a response in the next hour. The IP in the file — copper traces, pad positions, drill metadata — encoded their product, and they refused to upload it to a “free online Gerber viewer” they hadn’t vetted.
The combination of constraints — Mac/iPad device, time pressure, can’t upload — is the gap that Bluebeam Revu used to fill until they killed the iPad app in late 2025. Nothing replaced it.
A Gerber viewer running entirely in the browser tab, no upload. Tested on iPad Safari, iPhone Safari, Android Chrome, every desktop browser. Total bundle weight for the viewer (worker + renderer + UI) is around 800 KB compressed. Smaller than most native CAD viewers’ splash screens.
Key pieces:
Aperture macros. The Gerber spec lets a board designer define custom aperture shapes via parameterised macros. The spec is small but expressive — circles, rectangles, ovals, custom polygons, with rotation, scaling, hole-cutouts. Most boards use a handful of common macros. Some boards use thirty nested macros. The parser has to handle both.
Tessellation at small zoom levels. A modern 8-layer board with millions of geometry primitives takes hundreds of MB to expand fully into canvas-ready geometry. Loft’s own decompression cap doesn’t fit it on constrained devices. We solved this by lazy expansion (don’t parse layers until they’re shown) and tessellation simplification (skip features smaller than a pixel at the current zoom level). Both add complexity but bring large boards into range.
Touch input precision. Snap-to-pad measurement is finicky with finger taps. The first version was unusable on phone — you’d tap near a pad and the snap target was something else nearby. We added a tap-target halo (~16 px) and a magnifier popup on long-press. After that, measurement on phone became genuinely usable.
Renderer fallback. WebGL is faster but not every phone has reliable WebGL2 support. We ship both a Canvas2D and a WebGL path and pick based on capability detection at runtime. Most modern phones get the WebGL path; older or memory-constrained devices fall back to Canvas2D with simplified rendering.
Three things we considered and deferred:
Edit mode. This is read-only. No “draw a new trace.” A fully editable Gerber viewer is years of focused PCB-CAD work and a different product than the read-and-measure use case.
3D rendering. Some users want a 3D rendering of the board with components. Out of scope for now; the Gerber bundle alone doesn’t have enough information for full 3D (you’d need a board outline file plus component placement plus 3D models).
ODB++ and IPC-2581. Two newer manufacturing-bundle formats. Most boards still ship as Gerber X2 in 2026, but the newer formats are growing. We detect IPC-2581 and surface a clear error rather than silently failing; a full viewer for it would be a future cycle.
Mature open-source libraries got us most of the way. We didn’t write a Gerber parser from scratch — we built on tracespace v4 as the parse foundation and reimplemented the tight loops in TypeScript for Worker compatibility. The spec is open; the existing tooling is published. The value-add was the renderer
Touch UX is more than half the work for any mobile CAD tool. Desktop CAD assumes a precise pointer. Mobile CAD has to assume a finger. The tap-halo and long-press magnifier — two small features — were what made the viewer usable in the field.
Snapshot URLs were the killer feature for the original use case. The designer who emailed me ended up sending a Loft snapshot URL to the vendor as a response. The vendor opened the same view on their machine, saw the same measurements, and signed off. The whole exchange happened in under thirty minutes without anyone uploading the bundle. The URL serialiser turned out to be a small feature with outsized leverage — the whole exchange proved that in the first use.
Very large boards on phone. Multi-layer boards above roughly 8 layers with high primitive counts may hit memory limits on iPhone. We surface a warning when we detect a large file ahead of rendering. Desktop handles them comfortably; the phone gap is real.
X2 netlist tracing. We render geometry; we don’t trace connectivity through the netlist information that X2 carries. Some advanced workflows want this. On the to-do list.
Multi-board panels. Boards shipped in panels (multiple copies of a single design tiled on the manufacturing sheet) sometimes have non-standard origin offsets. We handle the common cases; weird cases get rendered with the wrong board extents.
The Gerber Viewer is at /tools/open-tools/gerber-viewer/. The Ucamco specification is at ucamco.com/en/gerber/gerber-format-specification.
The designer emailed back two weeks after the original exchange. The board passed first-article inspection. He sent a picture of the finished panel. I’m pretty sure that was the moment Loft stopped being a hobby project for me.
