diff --git a/shared/src/traceData.ts b/shared/src/traceData.ts
index 4516821..6795042 100644
--- a/shared/src/traceData.ts
+++ b/shared/src/traceData.ts
@@ -6,7 +6,7 @@ export const typeLine = z.object({
   intrinsicName: z.string().optional(),
   recursionId: z.number().optional(),
   flags: z.array(z.string()).optional(),
-  ts: z.number(),
+  ts: z.number().optional(),
   dur: z.number().optional(),
   display: z.string().optional(),
 })
@@ -39,3 +39,29 @@ export type DataLine = TraceLine | TypeLine
 
 export type TraceData = z.infer<typeof traceData>
 export const traceData = z.array(typeLine.or(traceLine))
+
+export interface TraceDataSummary {
+  totalTypes: number
+  timestampedTypes: number
+  untimestampedTypes: number
+  parseWarning?: string
+}
+
+export function hasTypeTimestamp(line: TypeLine): line is TypeLine & { ts: number } {
+  return typeof line.ts === 'number'
+}
+
+export function getTraceDataSummary(data: TraceData): TraceDataSummary {
+  const typeLines = data.filter((line): line is TypeLine => 'id' in line)
+  const timestampedTypes = typeLines.filter(hasTypeTimestamp).length
+  const untimestampedTypes = typeLines.length - timestampedTypes
+
+  return {
+    totalTypes: typeLines.length,
+    timestampedTypes,
+    untimestampedTypes,
+    parseWarning: untimestampedTypes > 0
+      ? `${untimestampedTypes} type entr${untimestampedTypes === 1 ? 'y is' : 'ies are'} missing timestamps and cannot be attributed to trace spans.`
+      : undefined,
+  }
+}
diff --git a/src/traceTree.ts b/src/traceTree.ts
index 0618d33..636518b 100644
--- a/src/traceTree.ts
+++ b/src/traceTree.ts
@@ -1,6 +1,6 @@
 import { isAbsolute, join, relative } from 'node:path'
 import type { FileStat } from '../shared/src/messages'
-import type { TraceData, TraceLine, TypeLine } from '../shared/src/traceData'
+import { type TraceData, type TraceLine, type TypeLine, hasTypeTimestamp } from '../shared/src/traceData'
 import { getWorkspacePath } from './storage'
 import { postMessage } from './webview'
 import { traceFiles } from './appState'
@@ -27,6 +27,10 @@ function getRoot(): Tree {
 }
 
 let treeIndexes: Tree[] = []
+function hasTraceTimestamp(line: TraceData[number]): line is TraceLine | TypeLine & { ts: number } {
+  return 'cat' in line || ('id' in line && hasTypeTimestamp(line))
+}
+
 export function toTree(traceData: TraceData, workspacePath: string): Tree {
   const tree: Tree = { ...getRoot() }
   let endTs = Number.MAX_SAFE_INTEGER
@@ -38,7 +42,7 @@ export function toTree(traceData: TraceData, workspacePath: string): Tree {
 
   treeIndexes = [tree]
 
-  const data = traceData.filter(x => 'id' in x || ('cat' in x)).sort((a, b) => a.ts - b.ts)
+  const data = traceData.filter(hasTraceTimestamp).sort((a, b) => a.ts - b.ts)
   // const data = traceData.filter(x => 'id' in x || ('cat' in x && x.cat?.startsWith('check'))).sort((a, b) => a.ts - b.ts)
   for (const line of data) {
     if ('args' in line && line.args?.path && isAbsolute(line.args?.path))
diff --git a/test/traceData.test.ts b/test/traceData.test.ts
new file mode 100644
index 0000000..1f3bbbd
--- /dev/null
+++ b/test/traceData.test.ts
@@ -0,0 +1,69 @@
+import { describe, expect, it } from 'vitest'
+import { getTraceDataSummary, traceData } from '../shared/src/traceData'
+
+describe('traceData', () => {
+  it('parses trace events', () => {
+    const result = traceData.safeParse([
+      {
+        pid: 1,
+        tid: 1,
+        ph: 'X',
+        cat: 'check',
+        ts: 10,
+        name: 'checkSourceFile',
+        dur: 20,
+        args: { path: '/workspace/src/index.ts', pos: 1, end: 2 },
+      },
+    ])
+
+    expect(result.success).toBe(true)
+  })
+
+  it('parses timestamped types', () => {
+    const result = traceData.safeParse([
+      {
+        id: 1,
+        intrinsicName: 'string',
+        recursionId: 1,
+        flags: ['String'],
+        ts: 12,
+        dur: 1,
+        display: 'string',
+      },
+    ])
+
+    expect(result.success).toBe(true)
+    expect(result.success && getTraceDataSummary(result.data)).toEqual({
+      totalTypes: 1,
+      timestampedTypes: 1,
+      untimestampedTypes: 0,
+      parseWarning: undefined,
+    })
+  })
+
+  it('parses untimestamped stock TypeScript types', () => {
+    const result = traceData.safeParse([
+      {
+        id: 1,
+        intrinsicName: 'string',
+        recursionId: 1,
+        flags: ['String'],
+        display: 'string',
+      },
+      {
+        id: 2,
+        recursionId: 2,
+        flags: ['Object'],
+        display: '{ value: string }',
+      },
+    ])
+
+    expect(result.success).toBe(true)
+    expect(result.success && getTraceDataSummary(result.data)).toEqual({
+      totalTypes: 2,
+      timestampedTypes: 0,
+      untimestampedTypes: 2,
+      parseWarning: '2 type entries are missing timestamps and cannot be attributed to trace spans.',
+    })
+  })
+})
diff --git a/test/traceTree.test.ts b/test/traceTree.test.ts
new file mode 100644
index 0000000..0472820
--- /dev/null
+++ b/test/traceTree.test.ts
@@ -0,0 +1,65 @@
+import { describe, expect, it, vi } from 'vitest'
+import { toTree } from '../src/traceTree'
+import type { TraceData } from '../shared/src/traceData'
+
+vi.mock('../src/storage', () => ({
+  getWorkspacePath: vi.fn(() => '/workspace'),
+}))
+
+vi.mock('../src/webview', () => ({
+  postMessage: vi.fn(),
+}))
+
+vi.mock('../src/appState', () => ({
+  traceFiles: { value: {} },
+}))
+
+vi.mock('vscode', () => ({
+  workspace: {
+    workspaceFolders: [{ uri: { fsPath: '/workspace' } }],
+    getConfiguration: vi.fn(() => ({
+      get: vi.fn(),
+    })),
+    onDidChangeConfiguration: vi.fn(),
+  },
+  window: {
+    showErrorMessage: vi.fn(),
+    createOutputChannel: vi.fn(() => ({
+      appendLine: vi.fn(),
+      show: vi.fn(),
+    })),
+  },
+  env: {
+    appRoot: '/Applications/Visual Studio Code.app',
+  },
+}))
+
+describe('traceTree', () => {
+  it('does not crash or attribute untimestamped types', () => {
+    const data: TraceData = [
+      {
+        pid: 1,
+        tid: 1,
+        ph: 'X',
+        cat: 'check',
+        ts: 10,
+        name: 'checkSourceFile',
+        dur: 20,
+        args: { path: '/workspace/src/index.ts', pos: 1, end: 2 },
+      },
+      {
+        id: 1,
+        intrinsicName: 'string',
+        recursionId: 1,
+        flags: ['String'],
+        display: 'string',
+      },
+    ]
+
+    const tree = toTree(data, '/workspace')
+
+    expect(tree.children).toHaveLength(1)
+    expect(tree.children[0].types).toHaveLength(0)
+    expect(tree.children[0].typeCnt).toBe(0)
+  })
+})