diff --git a/packages/trace-viewer/src/sw.ts b/packages/trace-viewer/src/sw.ts
index 980f0fee9d..e3d69fdf12 100644
--- a/packages/trace-viewer/src/sw.ts
+++ b/packages/trace-viewer/src/sw.ts
@@ -35,15 +35,27 @@ const loadedTraces = new Map<string, { traceModel: TraceModel, snapshotServer: S
 
 const clientIdToTraceUrls = new MultiMap<string, string>();
 
-async function loadTrace(trace: string, clientId: string, progress: (done: number, total: number) => void): Promise<TraceModel> {
-  const entry = loadedTraces.get(trace);
-  clientIdToTraceUrls.set(clientId, trace);
+async function loadTrace(traceUrl: string, traceFileName: string | null, clientId: string, progress: (done: number, total: number) => void): Promise<TraceModel> {
+  const entry = loadedTraces.get(traceUrl);
+  clientIdToTraceUrls.set(clientId, traceUrl);
   if (entry)
     return entry.traceModel;
   const traceModel = new TraceModel();
-  await traceModel.load(trace, progress);
+  try {
+    await traceModel.load(traceUrl, progress);
+  } catch (error: any) {
+    // eslint-disable-next-line no-console
+    console.error(error);
+
+    if (error?.message?.includes('Cannot find .trace file') && await traceModel.hasEntry('index.html'))
+      throw new Error('Could not load trace. Did you upload a Playwright HTML report instead? Make sure to extract the archive first and then double-click the index.html file or put it on a web server.');
+    else if (traceFileName)
+      throw new Error(`Could not load trace from ${traceFileName}. Make sure to upload a valid Playwright trace.`);
+    else
+      throw new Error(`Could not load trace from ${traceUrl}. Make sure a valid Playwright Trace is accessible over this url.`);
+  }
   const snapshotServer = new SnapshotServer(traceModel.storage());
-  loadedTraces.set(trace, { traceModel, snapshotServer });
+  loadedTraces.set(traceUrl, { traceModel, snapshotServer });
   return traceModel;
 }
 
@@ -65,21 +77,15 @@ async function doFetch(event: FetchEvent): Promise<Response> {
 
     if (relativePath === '/context') {
       try {
-        const traceModel = await loadTrace(traceUrl, event.clientId, (done: number, total: number) => {
+        const traceModel = await loadTrace(traceUrl, url.searchParams.get('traceFileName'), event.clientId, (done: number, total: number) => {
           client.postMessage({ method: 'progress', params: { done, total } });
         });
         return new Response(JSON.stringify(traceModel!.contextEntry), {
           status: 200,
           headers: { 'Content-Type': 'application/json' }
         });
-      } catch (error: unknown) {
-        // eslint-disable-next-line no-console
-        console.error(error);
-        const traceFileName = url.searchParams.get('traceFileName')!;
-        return new Response(JSON.stringify({
-          error: traceFileName ? `Could not load trace from ${traceFileName}. Make sure to upload a valid Playwright trace.` :
-            `Could not load trace from ${traceUrl}. Make sure a valid Playwright Trace is accessible over this url.`,
-        }), {
+      } catch (error: any) {
+        return new Response(JSON.stringify({ error: error?.message }), {
           status: 500,
           headers: { 'Content-Type': 'application/json' }
         });
diff --git a/packages/trace-viewer/src/traceModel.ts b/packages/trace-viewer/src/traceModel.ts
index 24b313e813..a9baa29baf 100644
--- a/packages/trace-viewer/src/traceModel.ts
+++ b/packages/trace-viewer/src/traceModel.ts
@@ -31,6 +31,7 @@ export class TraceModel {
   private _snapshotStorage: PersistentSnapshotStorage | undefined;
   private _entries = new Map<string, zip.Entry>();
   private _version: number | undefined;
+  private _zipReader: zip.ZipReader | undefined;
 
   constructor() {
     this.contextEntry = createEmptyContext();
@@ -46,12 +47,12 @@ export class TraceModel {
 
   async load(traceURL: string, progress: (done: number, total: number) => void) {
     this.contextEntry.traceUrl = traceURL;
-    const zipReader = new zipjs.ZipReader( // @ts-ignore
+    this._zipReader = new zipjs.ZipReader( // @ts-ignore
         new zipjs.HttpReader(this._formatUrl(traceURL), { mode: 'cors', preventHeadRequest: true }),
         { useWebWorkers: false }) as zip.ZipReader;
     let traceEntry: zip.Entry | undefined;
     let networkEntry: zip.Entry | undefined;
-    for (const entry of await zipReader.getEntries({ onprogress: progress })) {
+    for (const entry of await this._zipReader.getEntries({ onprogress: progress })) {
       if (entry.filename.endsWith('.trace'))
         traceEntry = entry;
       if (entry.filename.endsWith('.network'))
@@ -60,10 +61,13 @@ export class TraceModel {
         this.contextEntry.hasSource = true;
       this._entries.set(entry.filename, entry);
     }
+    if (!traceEntry)
+      throw new Error('Cannot find .trace file');
+
     this._snapshotStorage = new PersistentSnapshotStorage(this._entries);
 
     const traceWriter = new zipjs.TextWriter() as zip.TextWriter;
-    await traceEntry!.getData!(traceWriter);
+    await traceEntry.getData!(traceWriter);
     for (const line of (await traceWriter.getData()).split('\n'))
       this.appendEvent(line);
 
@@ -76,6 +80,16 @@ export class TraceModel {
     this._build();
   }
 
+  async hasEntry(filename: string): Promise<boolean> {
+    if (!this._zipReader)
+      return false;
+    for (const entry of await this._zipReader.getEntries()) {
+      if (entry.filename === filename)
+        return true;
+    }
+    return false;
+  }
+
   async resourceForSha1(sha1: string): Promise<Blob | undefined> {
     const entry = this._entries.get('resources/' + sha1);
     if (!entry)
diff --git a/utils/build/build.js b/utils/build/build.js
index 3f11ceee84..970fed9c70 100644
--- a/utils/build/build.js
+++ b/utils/build/build.js
@@ -286,7 +286,7 @@ for (const webPackage of ['html-reporter', 'recorder', 'trace-viewer']) {
       `packages/web/src/`,
     ],
     command: 'npx',
-    args: ['vite', 'build'],
+    args: ['vite', 'build', ...(watchMode ? ['--sourcemap'] : [])],
     cwd: path.join(__dirname, '..', '..', 'packages', webPackage),
   });
 }
@@ -335,7 +335,7 @@ if (lintMode) {
       command: 'npx',
       args: ['tsc', ...(watchMode ? ['-w'] : []), '-p', quotePath(filePath(`packages/${webPackage}`))],
       shell: true,
-    });  
+    });
   }
 }