diff --git a/app/vibenet/library/format.test.ts b/app/vibenet/library/format.test.ts
new file mode 100644
index 0000000..24119d8
--- /dev/null
+++ b/app/vibenet/library/format.test.ts
@@ -0,0 +1,18 @@
+import { describe, expect, it } from 'vitest';
+
+import { formatAmount } from './format';
+
+describe('formatAmount', () => {
+  it('formats positive fractional amounts', () => {
+    expect(formatAmount('1500000000000000000', 18)).toBe('1.5');
+  });
+
+  it('keeps the sign separate when formatting negative amounts', () => {
+    expect(formatAmount('-1500000000000000000', 18)).toBe('-1.5');
+    expect(formatAmount('-500000000000000000', 18)).toBe('-0.5');
+  });
+
+  it('returns the original raw value when it cannot parse an amount', () => {
+    expect(formatAmount('not-a-number', 18)).toBe('not-a-number');
+  });
+});
diff --git a/app/vibenet/library/format.ts b/app/vibenet/library/format.ts
index 4f2550d..d608385 100644
--- a/app/vibenet/library/format.ts
+++ b/app/vibenet/library/format.ts
@@ -32,14 +32,16 @@ export function formatAmount(raw: string, decimals: number, maxFractionDigits =
   try {
     const value = BigInt(raw);
     if (value === 0n) return '0';
+    const sign = value < 0n ? '-' : '';
+    const magnitude = value < 0n ? -value : value;
     const divisor = 10n ** BigInt(decimals);
-    const whole = (value / divisor).toLocaleString();
-    const frac = (value % divisor)
+    const whole = (magnitude / divisor).toLocaleString();
+    const frac = (magnitude % divisor)
       .toString()
       .padStart(decimals, '0')
       .slice(0, maxFractionDigits)
       .replace(/0+$/, '');
-    return frac ? `${whole}.${frac}` : whole;
+    return frac ? `${sign}${whole}.${frac}` : `${sign}${whole}`;
   } catch {
     return raw;
   }