diff --git a/src/report.ts b/src/report.ts
new file mode 100644
index 0000000..830b9f8
--- /dev/null
+++ b/src/report.ts
@@ -0,0 +1,9 @@
+import type { TraceReport } from './model';
+
+export function formatReport(report: TraceReport): string {
+  const lines = [`覆盖率 ${report.percent}% (${report.covered}/${report.total})`];
+  for (const gap of report.gaps) lines.push(`${gap.requirementId}: ${gap.reason}`);
+  if (report.orphanCases.length) lines.push(`无效关联: ${report.orphanCases.join(', ')}`);
+  if (report.duplicateCases.length) lines.push(`重复用例: ${report.duplicateCases.join(', ')}`);
+  return lines.join('\n');
+}