SimCrux — RTL Regressions in the Test Explorer

A failing formal property should not end at a log line and a file path.

SimCrux puts your RTL regression in VSCode's Test Explorer, runs it as a task, and — when a bounded proof fails — opens the counterexample trace in a waveform tab beside the failing property. That last step is the reason this extension exists.

Registries: Marketplace · Open VSX (Cursor, Windsurf, VSCodium, Theia)
Licence: Apache-2.0 · Home: simcrux.app

What it does

The regression is a test tree before anything has run. simcrux.yaml's suites and tests become TestItems immediately; a results.ndjson then decorates them with per-test state, duration and inline failure messages. You see the shape of the regression without waiting for it.

Failing proof → waveform beside it. A failing bounded proof records its counterexample on the result row. One command opens that VCD in the WaveCrux tab next to the test tree, so the property and the trace that refutes it are on screen together. If WaveCrux is not installed you get a sentence saying so and a link — not a broken command. If the trace was recorded on a CI farm and is not on this machine, it says that instead of opening an empty editor.

The formal verdict survives. Five SymbiYosys outcomes collapse into VSCode's single TestStatus.fail. A tree driven by status alone would render counterexample found and the engine could not decide identically — which is the difference between "you have a bug" and "you have no answer". The verdict is carried into the item description, into a filterable TestTag, and into the failure message. Only a genuine refutation ever offers a counterexample.

Run it from here. A simcrux task type runs simcrux <config> --ci, which is what writes the results file the tree reads. Simulator output is linked: source references like tb.sv:128:7 and SymbiYosys trace announcements become clickable in the terminal.

Getting started

Open a workspace containing a simcrux.yaml.
Open the Test Explorer — the suites and tests are already there.
Run the simcrux task, or run your regression however you normally do.
Right-click a failing formal property → Open Counterexample in WaveCrux.

Part of a suite that talks to itself

SimCrux, WaveCrux, LintCrux and NetCrux speak CXP, a cross-process peer protocol — so this window can be a peer of a running desktop Crux session, not only of other extensions. Your VSCode window is one CXP peer no matter how many of the four you install: one identity, one manifest, one heartbeat.

Install the EDACrux Suite pack to get all four at once.

Settings

Setting	Default	What it names
`edacrux.sim.projectFile`	`simcrux.yaml`	The project config this window works against
`edacrux.sim.resultsPath`	(derived)	Empty means the config's `output.results_path`, else `results.ndjson` beside the config
`edacrux.sim.executable`	`simcrux`	The binary the regression task runs
`edacrux.crossProbe.revealSelection`	`true`	Bring the matching tab forward when a connected Crux app announces a selection
`edacrux.crossProbe.openSourceFocusesEditor`	`true`	Move the cursor into the editor when a peer asks to open a source location
`edacrux.crossProbe.followWaveformSelection`	`false`	With WaveCrux installed: reveal a signal's RTL declaration when you select it in a waveform tab in this window

Commands

Command	Id
Refresh Regression Results	`simcrux.refreshResults`
Run Regression	`simcrux.runRegression`
Open Counterexample in WaveCrux	`simcrux.openCounterexample`
Open This Project in SimCrux Desktop	`simcrux.openHistoryInDesktop`
Send Selection to Crux App	`edacrux.sendSelectionToPeer`
Highlight Selection in Crux App	`edacrux.highlightSelectionInPeer`
Open Capabilities Panel	`edacrux.openCapabilitiesPanel`

What this extension does not do — stated plainly

No run history. Flakiness detection, trends, run-to-run comparison, and any view of a CI fleet or simulation farm need a database rather than a file in a workspace. That is SimCrux Desktop's job, and Open This Project in SimCrux Desktop is the handoff.
One config per window. The CLI takes one config per run, so the test tree, the task and the counterexample handoff all agree on which — rather than quietly disagreeing.
Restricted workspaces. This extension declares no untrusted-workspace support, so it stays inert until you trust the folder.

Telemetry

Off unless you have VSCode telemetry on. The extension checks vscode.env.isTelemetryEnabled at send time, not once at startup.

Localization

English, 简体中文, 日本語 and 한국어 — hand-translated, commands and settings included.

The rest of the suite

Extension	What it is for
WaveCrux	Nine protocol decoders, X-trace, waveform diff, FSM views — on VCD/FST/GHW in an editor tab
LintCrux	RTL lint results as Problems-panel diagnostics, with waivers filed from a quick fix
NetCrux	"What drives this signal?" on a selection, resolved through the stems index
EDACrux Suite	All four, installed together

Built by Ferrite Engineering. Apache-2.0. edacrux.app