diff --git a/src/common/emucore.ts b/src/common/emucore.ts
index f9510da9..9b3411ec 100644
--- a/src/common/emucore.ts
+++ b/src/common/emucore.ts
@@ -401,6 +401,9 @@ export class EmuCore {
   }
 
   getVideo(): VideoOutput | null {
+    // verilog sets hasvideo on ROM load; a design with no vsync/hsync/rgb
+    // leaves the headless raster blank, which isn't a failure to draw
+    if ((this.platform as any).hasvideo === false) return null;
     return this.captured?.() ?? this.video?.get() ?? null;
   }
 
diff --git a/src/platform/williams.ts b/src/platform/williams.ts
index 2ab27511..67bc8796 100644
--- a/src/platform/williams.ts
+++ b/src/platform/williams.ts
@@ -303,14 +303,17 @@ var WilliamsPlatform = function(mainElement, proto, options) {
     cpu = self.newCPU(membus, iobus);
 
     audio = new MasterAudio();
-    worker = new Worker("./src/common/audio/z80worker.js");
-    workerchannel = new WorkerSoundChannel(worker);
-    audio.master.addChannel(workerchannel);
+    // the sound board runs in a web worker; headless (node) has no sound
+    if (typeof Worker !== 'undefined') {
+      worker = new Worker("./src/common/audio/z80worker.js");
+      workerchannel = new WorkerSoundChannel(worker);
+      audio.master.addChannel(workerchannel);
+    }
 
     let rotate = options?.rotate == null ? -90 : parseFloat(options.rotate);
     video = new RasterVideo(mainElement, SCREEN_WIDTH, SCREEN_HEIGHT, { rotate });
     video.create();
-    $(video.canvas).click(function(e) {
+    if (typeof $ !== 'undefined') $(video.canvas).click(function(e) {
       var x = Math.floor(e.offsetX * video.canvas.width / $(video.canvas).width());
       var y = Math.floor(e.offsetY * video.canvas.height / $(video.canvas).height());
       var addr = (x >> 3) + (y * 32) + 0x400;
@@ -359,7 +362,7 @@ var WilliamsPlatform = function(mainElement, proto, options) {
   this.loadSoundROM = function(data) {
     console.log("loading sound ROM " + data.length + " bytes");
     var soundrom = padBytes(data, 0x4000);
-    worker.postMessage({ rom: soundrom });
+    if (worker) worker.postMessage({ rom: soundrom });
   }
 
   this.loadROM = function(title, data) {
diff --git a/src/tools/buildpresets.ts b/src/tools/buildpresets.ts
index b81ee35a..c2fb9953 100644
--- a/src/tools/buildpresets.ts
+++ b/src/tools/buildpresets.ts
@@ -49,7 +49,7 @@ const PLATFORM_SRC_DIR = 'src/platform';
 export interface RunResult {
     ok: boolean;            // platform started and ran without throwing
     frames: number;         // frames actually advanced
-    verdict: 'ok' | 'solid' | 'blank' | 'novideo' | 'halted' | 'error';
+    verdict: 'ok' | 'solid' | 'blank' | 'novideo' | 'skipped' | 'halted' | 'error';
     width?: number;
     height?: number;
     colors?: number;        // distinct pixel colors on the last frame
@@ -93,8 +93,8 @@ const DEFAULT_TIMEOUT = 120000;
 const DEFAULT_RUN_FRAMES = 300;
 
 // A frame this uniform after a few seconds almost always means nothing drew;
-// a real screen has a background plus text or sprites.
-const SOLID_FRACTION = 0.999;
+// a real screen has a background plus text or sprites (or stars).
+const SOLID_FRACTION = 0.9995;
 
 // skip these platforms, they aren't ready yet or otherwise broken
 const SKIP_PLATFORMS = [
@@ -105,6 +105,10 @@ const SKIP_PLATFORMS = [
     'vectrex',
 ];
 
+// build these, but don't run them: the emulator needs a real browser
+// (x86 is the v86 PC emulator, loaded as a page script)
+const NO_RUN_PLATFORMS = ['x86'];
+
 // Load every platform module so it registers itself in PLATFORMS. A couple of
 // them touch the DOM at import time and can't run here; they're reported
 // rather than hidden.
@@ -482,6 +486,9 @@ export async function runPreset(
     const started = Date.now();
     const frames = opts.frames || DEFAULT_RUN_FRAMES;
     const run: RunResult = { ok: false, frames, verdict: 'error', ms: 0 };
+    if (NO_RUN_PLATFORMS.includes(platform)) {
+        return { ...run, ok: true, frames: 0, verdict: 'skipped' };
+    }
     const capture = opts.verbose ? null : captureOutput();
     let target: EmuTarget | null = null;
     try {
@@ -630,6 +637,7 @@ function runStatus(run: RunResult): string {
         case 'ok': return green('run ok') + ' ' + dim(info);
         case 'halted': return dim('run halted') + ' ' + dim(info);
         case 'novideo': return dim('run: no video');
+        case 'skipped': return dim('run: skipped (needs browser)');
         case 'blank': return yellow(bold('run BLANK')) + ' ' + dim(info);
         case 'solid': return yellow(bold('run SOLID')) + ' ' + dim(info);
         default: return red(bold('run FAIL')) + ' ' + dim(info);
@@ -690,7 +698,7 @@ async function main() {
     console.log(bold(`${run ? 'building and running' : 'building'} ${presets.length} presets...`));
     const results = await buildAllPresets({
         presets, timeout, verbose, run, frames, pngDir, onResult: (r) => {
-            const clean = !r.run || r.run.verdict === 'ok' || r.run.verdict === 'novideo' || r.run.verdict === 'halted';
+            const clean = !r.run || r.run.verdict === 'ok' || r.run.verdict === 'novideo' || r.run.verdict === 'skipped' || r.run.verdict === 'halted';
             if (quiet && r.ok && clean) return;
             const status = r.ok ? green('ok  ') : red(bold('FAIL'));
             const size = r.size != null ? `${r.size} bytes` : '';
@@ -729,7 +737,7 @@ async function main() {
     // what the builds did when loaded, separately from whether they built
     const ran = results.filter((r) => r.run);
     if (ran.length) {
-        const problems = ran.filter((r) => r.run.verdict !== 'ok' && r.run.verdict !== 'novideo' && r.run.verdict !== 'halted');
+        const problems = ran.filter((r) => r.run.verdict !== 'ok' && r.run.verdict !== 'novideo' && r.run.verdict !== 'skipped' && r.run.verdict !== 'halted');
         const tally2 = `${ran.length - problems.length}/${ran.length} presets run clean`;
         console.log('\n' + bold(problems.length ? yellow(tally2) : green(tally2)));
         if (problems.length) {