What a migration quietly changes in a SchDoc — and the viewer we're building to show it.
Read the sheet — symbols, wires, nets and labels — right in your browser. The migration-readiness inspector lands at launch. Below the viewer: exactly where a schematic migration goes wrong — net assignment, buses, harnesses and channel designators — with the KiCad evidence for each.
The viewer is live. The inspector lands at launch.
The surface above reads your .SchDoc directly in your browser — symbols, pins, wires, buses, junctions, net labels, power ports and text, rendered locally in the file's own colours, with net highlighting as wired on the sheet. Nothing is uploaded and no account is needed. What lands at launch is the inspector on top of it: the migration-readiness read of the exact sheet you opened.
A viewer shows you the drawing. An inspector shows you what a migration would change.
Plenty of tools will render your schematic so you can look at it. That answers "what does this sheet contain?" — not the question that actually matters before a migration: "will this connectivity still mean the same thing in KiCad?" The symbols come across; the wiring is where a standard migration can quietly differ. A merged net, a bus member that arrives detached, a channel suffix that gets stripped — each leaves a schematic that opens and passes a glance while the netlist underneath has shifted. Every change-mode below is documented in KiCad's own docs or public tracker. Crosspad's inspector is being built to make each one visible on your file — before it reaches your board.
Looking at the schematic isn't the same as knowing it will migrate.
What it will do: open the file, read the connectivity, show the migration risk.
One free tool, two jobs — a schematic viewer that runs in your browser today, and a migration-readiness inspector on the same file at launch.
- Open a .SchDoc in the browser
It reads an Altium .SchDoc and draws the schematic — no Altium licence, no install, on any OS.
- See the wiring
Highlight a net as it is wired on the sheet — wires, junctions, labels, power ports and pins. Buses and hierarchical sheets are shown, and named as not resolved.
- Inspect for migration risk (lands at launch)
It will flag the constructs a standard Altium → KiCad migration can silently change — before you migrate.
- Grounded in public evidence
Every flag will map to a documented KiCad import behaviour — its own docs or a tracked issue ID — not our opinion.
- Hand you to the real check
A viewer renders and flags; it never returns a migration verdict. When a file looks risky, the readiness answer comes from the migration analysis — which runs on a .PcbDoc.
The viewer will inspect a schematic — it will not migrate it, and it will not judge whether a design migrates cleanly: that verdict comes from the migration analysis, never from a browser tab. The migration and its evidence report are the paid product.
What the viewer counted on your sheet.
These are counts, not judgements: the objects this reading found in the file you just opened. The migration-readiness read of the same sheet is the inspector, and it lands at launch.
Altium doesn't run on macOS or Linux. This does.
Altium ships no native macOS or Linux build, so on those machines you can't open your own schematic in the tool that drew it — which is often why the project is heading to KiCad in the first place. This viewer is a browser tab: it opens the .SchDoc on whatever you are sitting at, without a licence, an install or a virtual machine, and without sending the file anywhere.
- On macOS
Open and read a .SchDoc without a Windows VM or a Parallels licence — symbols, wires, nets and labels, in the browser you already have.
- On Linux
No Wine, no dual boot: the sheet is parsed and drawn by the page itself, so a Linux desktop reads it exactly as a Windows one does.
Where a standard Altium → KiCad migration can quietly change one schematic.
These are the connectivity change-modes the inspector is being built to surface. Each is grounded in KiCad's own import docs or public issue tracker, and several are version-specific (documented against KiCad 10.0.6, 2026-08-29). The schematic opens either way — which is exactly why an independent inspection matters.
- Net assignment & labels
Two labels that meant one net at the source — or one that meant two — can end up assigned differently, and KiCad's own import docs record net-name and case edge cases in how Altium nets come across. Nothing errors; the netlist just means something slightly different.
documented: KiCad import dev-docs (net-name / case) - Buses (shared-member)
Buses whose members share a name are where connectivity has broken silently before: on KiCad ≤10.0.4 those members could arrive unconnected — valid in Altium, disconnected after.
documented: KiCad #20707 (≤10.0.4; fixed 10.0.5) - Harness connectivity
Signal-harness objects are among the constructs a standard migration handles least completely — they can come across only partially, and have been reported crashing the import outright.
documented: KiCad #8741 / #16852 - Channel (repeated-sheet) designators
When a sheet is reused as a channel, the suffix that keeps C33A and C33B apart can be stripped (C33A / C33B → C33), collapsing distinct parts into duplicate references and breaking the BOM and netlist.
documented: KiCad #24861 / #23709 - Title-block variables & metadata
A variable reference like ${PCB_REVISION} in a title block can render as literal text instead of its value, and KiCad's import docs list parameter sets among elements not imported — the symbols are right; the revision on the sheet is wrong.
documented: KiCad #24455 + import dev-docs - Not-imported schematic elements
KiCad's own import docs enumerate what doesn't come across — IEEE standard symbols, parameter sets, and SPICE model data (parsed but not simulated) — and older files whose encoding isn't preserved can arrive with mangled text.
documented: KiCad import dev-docs
Migrating a multi-sheet project — hierarchy, cross-sheet ports — is a different, harder class of problem (complex hierarchies can fail where simple ones succeed, KiCad #20936). That's the multi-sheet schematics page.
Change-modes reflect a standard Altium → KiCad migration of an Altium .SchDoc as of KiCad 10.0.6 (2026-08-29). Behavior changes most releases — the shared-member bus issue (#20707), for example, was fixed in 10.0.5 and is scoped ≤10.0.4. Version-specific modes are noted, and this page is updated per release. The viewer is live; the inspector ships with the engine at launch.
A readiness read on your schematic — not just a picture of it.
- NetsINSPECTED
- Net labelsINSPECTED
- Bus SPI_DATAWATCH
- Harness USB_IFREVIEW
- Channel designatorsREVIEW
- Title-block ${REVISION}WATCH
- ASCII / non-binary .SchDocUNSUPPORTED
| FINDING | DETAIL | READINESS |
|---|---|---|
| Nets | read from the sheet | INSPECTED |
| Net labels | assignment read against source | INSPECTED |
| Bus SPI_DATA | shared-member connectivity (≤10.0.4 risk) | WATCH |
| Harness USB_IF | partial-import risk | REVIEW BEFORE MIGRATING |
| Channel designators | R*_CH2 collision risk | REVIEW BEFORE MIGRATING |
| Title-block ${REVISION} | variable may render literally | WATCH |
| ASCII / non-binary .SchDoc | container and header check | UNSUPPORTED (named) |
Plenty of tools render the board. Almost none read the schematic.
Free viewers for the PCB side are common, and good — the strongest independent ones render the board, its layers and its 3D. The schematic side is where the tooling thins out: the leading independent PcbDoc viewer renders the board only, with no .SchDoc view at all. So the engineer who just needs to open a schematic — often on a Mac or Linux box that can't run Altium in the first place — is under-served. Crosspad is being built for that gap, and for the part that actually decides a migration: not "what's on this sheet," but "what would change if this sheet moved to KiCad."
Which schematics it will read — and what it won't pretend to.
The viewer reads binary Altium schematics (.SchDoc). ASCII sheets, libraries, project files and damaged containers are named as unsupported, not silently skipped. What the viewer cannot draw, it counts and lists — never hides. The inspector reads risk; it does not migrate — where connectivity can't be proven equivalent, it flags a review rather than implying a clean pass. Nothing is uploaded: your file never leaves your browser.
Frequently asked questions.
How do I open a .SchDoc file without Altium?
Altium .SchDoc is a proprietary schematic format, but you don't need an Altium licence to read one. Crosspad's free SchDoc viewer opens it in the browser on any OS — nothing is uploaded, no account is needed. Our guide covers the other honest options too.
Is the SchDoc viewer free?
Yes — free, no account. Crosspad's paid product is the verified board migration; schematic files are outside the commercial-beta scope at launch — see the SchDoc → KiCad page.
Does it show the connectivity, or just the drawing?
It highlights nets as they are wired on the sheet; the migration-readiness flags land at launch with the inspector. The constructs the inspector will flag — net assignment, shared-member buses (KiCad #20707, ≤10.0.4), harnesses (#8741) and channel designators (#24861) — are documented on this page today.
Can it open several sheets at once?
Yes — drop as many .SchDoc files as you like and they open as tabs, with the connectivity read across them together. Hierarchy itself (sheet symbols, cross-sheet ports) is shown and named as not resolved, and migrating a multi-sheet project is a harder class of problem (complex hierarchies can fail where simple ones succeed, KiCad #20936); see the multi-sheet schematics page for that.
Is my schematic uploaded anywhere?
No. The viewer parses and renders your .SchDoc entirely in your browser — nothing is uploaded and no account is required. The readiness inspector lands at launch.
When does the migration-readiness inspector go live?
It ships with the engine at launch, on top of the viewer that is live today.
Is there an Altium schematic viewer for Mac or Linux?
Yes — this one runs in the browser on any OS, no Altium licence, no install.
Can I view a .SchDoc online without uploading it?
Yes. Crosspad's viewer reads the file in your browser; nothing leaves your machine — you can watch the network tab stay empty.
Know what a migration would touch — before you move your schematic.
Open the sheet here and read it — symbols, wires, nets and labels, in your browser. Then read what a standard KiCad migration can silently change: net assignment, buses, harnesses and channel designators, each with its KiCad evidence. When it's a board you need checked, the readiness scan runs on a .PcbDoc.
Free. No account required. Your file never leaves your browser.