A browser-native Verilog simulator and waveform viewer. Paste or load RTL, simulate it instantly with zero install, inspect waveforms with real logic-analyzer ergonomics.
The honest pitch: the fastest path from RTL idea to waveform on a screen — for education, interview prep, quick experiments, and embedding in docs and blog posts. Not a synthesis tool, not SystemVerilog-complete, not a Verilator replacement.
Above: owaveform simulating an unmodified third-party single-cycle CPU (jaywonchung/Verilog-Harvard-CPU), pasted straight into the editor — output matches Icarus Verilog exactly.
- Event-driven 4-state kernel (~400k cycles/s) with X propagation —
uninitialized regs read x, render red in the viewer, and answer "why is my
output x?" honestly — plus parameters, hierarchy, memories, functions,
initial/#ntestbenches, tristateinoutbuses,signedarithmetic, and`define/`includepreprocessing — every deviation from IEEE 1364 documented in SEMANTICS.md - Icarus Verilog as the oracle: a 200-seed differential fuzz corpus and per-feature diff tests run in CI; 500 random cases fuzz nightly
- Viewer built for scale: windowed LOD rendering (1M transitions / 500 signals under a 16ms frame budget), hierarchy tree with search, five radices, named markers with a Δ table, keyboard navigation, PAN/ZOOM drag modes
- VCD in and out: streaming quirk-tolerant reader (drag a Verilator/Icarus dump onto the wave pane) and writer
- Shareable: session sidecar JSON,
#src=URLs with the design compressed into the fragment, offline-capable PWA, dependency-free single-file build
pnpm install # also generates the parser from verilog.pegjs
pnpm dev # app dev server
pnpm test # all test suites
pnpm build:single # dependency-free dist/waveform.html
pnpm bench # perf budgets
pnpm diffuzz -n 100 # differential fuzz vs Icarus (brew/apt install iverilog)| Package | What it is |
|---|---|
@owaveform/grammar |
peggy grammar, preprocessor, and AST types for the subset |
@owaveform/kernel |
event-driven simulation kernel (no DOM) |
@owaveform/vcd |
streaming VCD reader/writer |
@owaveform/wave-view |
three.js waveform viewer component, framework-free |
@owaveform/app |
the web app, a thin shell over the packages |
The supported language subset and every deliberate deviation from IEEE 1364 are documented in SEMANTICS.md. Architecture decisions live in DECISIONS.md; the roadmap in plan.md; how to contribute in CONTRIBUTING.md.
waveform.html at the repo root is the original single-file prototype, kept frozen as
a reference. The equivalent artifact is now produced by pnpm build:single.
MIT. The single-file build inlines three.js (MIT, © three.js authors). Icarus Verilog is used only as a development-time test oracle and is not distributed with owaveform.