diff --git a/web/src/lib/format.ts b/web/src/lib/format.ts
new file mode 100644
index 0000000..225a773
--- /dev/null
+++ b/web/src/lib/format.ts
@@ -0,0 +1,78 @@
+import { localeOf, type Lang } from "./i18n";
+
+const DUR_UNITS: Record<Lang, { s: string; m: string; h: string; d: string }> = {
+  en: { s: "s", m: "m", h: "h", d: "d" },
+  fa: { s: "ث", m: "د", h: "س", d: "ر" },
+};
+
+export const pctSign = (lang: Lang) => (lang === "fa" ? "٪" : "%");
+
+export function fmtNumber(lang: Lang, value: number, digits = 0): string {
+  return new Intl.NumberFormat(localeOf(lang), {
+    minimumFractionDigits: digits,
+    maximumFractionDigits: digits,
+  }).format(value);
+}
+
+/** Uptime percent: "99.98" — trims to the precision that matters. */
+export function fmtUptime(lang: Lang, pct: number): string {
+  const digits = pct >= 100 ? 0 : pct >= 99 ? 2 : 1;
+  return fmtNumber(lang, pct, digits);
+}
+
+export function fmtLatency(lang: Lang, ms: number): string {
+  if (ms >= 1000) return `${fmtNumber(lang, ms / 1000, 2)}s`;
+  if (ms >= 100) return `${fmtNumber(lang, ms, 0)}ms`;
+  return `${fmtNumber(lang, ms, 1)}ms`;
+}
+
+export function fmtClock(lang: Lang, date: Date): string {
+  return new Intl.DateTimeFormat(localeOf(lang), {
+    hour: "2-digit",
+    minute: "2-digit",
+    second: "2-digit",
+    hour12: false,
+  }).format(date);
+}
+
+export function fmtTime(lang: Lang, ts: number): string {
+  return new Intl.DateTimeFormat(localeOf(lang), {
+    hour: "2-digit",
+    minute: "2-digit",
+    hour12: false,
+  }).format(new Date(ts));
+}
+
+export function fmtDate(lang: Lang, ts: number): string {
+  return new Intl.DateTimeFormat(localeOf(lang), {
+    month: "short",
+    day: "numeric",
+    hour: "2-digit",
+    minute: "2-digit",
+    hour12: false,
+  }).format(new Date(ts));
+}
+
+export function fmtHour(lang: Lang, hour: number): string {
+  return fmtNumber(lang, hour);
+}
+
+/** "3m 20s" style duration, localized digits and units. */
+export function fmtDuration(lang: Lang, ms: number): string {
+  const u = DUR_UNITS[lang];
+  const s = Math.max(0, Math.round(ms / 1000));
+  if (s < 60) return `${fmtNumber(lang, s)}${u.s}`;
+  const m = Math.floor(s / 60);
+  if (m < 60) return `${fmtNumber(lang, m)}${u.m} ${fmtNumber(lang, s % 60)}${u.s}`;
+  const h = Math.floor(m / 60);
+  if (h < 24) return `${fmtNumber(lang, h)}${u.h} ${fmtNumber(lang, m % 60)}${u.m}`;
+  const d = Math.floor(h / 24);
+  return `${fmtNumber(lang, d)}${u.d} ${fmtNumber(lang, h % 24)}${u.h}`;
+}
+
+/** Seconds → "15s" / "5m" for check intervals. */
+export function fmtInterval(lang: Lang, sec: number): string {
+  if (sec < 60) return `${fmtNumber(lang, sec)}s`;
+  if (sec < 3600) return `${fmtNumber(lang, Math.round(sec / 60))}m`;
+  return `${fmtNumber(lang, Math.round(sec / 3600))}h`;
+}