diff --git a/package.json b/package.json
index b090b320980..9dcbf411d38 100644
--- a/package.json
+++ b/package.json
@@ -34,7 +34,6 @@
     "@replit/codemirror-lang-svelte": "6.0.0",
     "@replit/codemirror-vscode-keymap": "6.0.2",
     "@resvg/resvg-wasm": "2.6.2",
-    "@silverwind/vue3-calendar-heatmap": "2.1.1",
     "@vitejs/plugin-vue": "6.0.6",
     "ansi_up": "6.0.6",
     "asciinema-player": "3.15.1",
diff --git a/pnpm-lock.yaml b/pnpm-lock.yaml
index a05156011e8..fdc569187a5 100644
--- a/pnpm-lock.yaml
+++ b/pnpm-lock.yaml
@@ -112,9 +112,6 @@ importers:
       '@resvg/resvg-wasm':
         specifier: 2.6.2
         version: 2.6.2
-      '@silverwind/vue3-calendar-heatmap':
-        specifier: 2.1.1
-        version: 2.1.1(tippy.js@6.3.7)(vue@3.5.32(typescript@6.0.2))
       '@vitejs/plugin-vue':
         specifier: 6.0.6
         version: 6.0.6(vite@8.0.8(@types/node@25.6.0)(esbuild@0.28.0)(jiti@2.6.1))(vue@3.5.32(typescript@6.0.2))
@@ -1249,13 +1246,6 @@ packages:
   '@scarf/scarf@1.4.0':
     resolution: {integrity: sha512-xxeapPiUXdZAE3che6f3xogoJPeZgig6omHEy1rIY5WVsB3H2BHNnZH+gHG6x91SCWyQCzWGsuL2Hh3ClO5/qQ==}
 
-  '@silverwind/vue3-calendar-heatmap@2.1.1':
-    resolution: {integrity: sha512-RQtLOpkysm0LR3PbUoc+aDcYxzy7xboygb1SQEwrUm2/XB2nmt0BEra2ADXpu4kwFxtk0+IyNwzFvbBai/wvTg==}
-    engines: {node: '>=16'}
-    peerDependencies:
-      tippy.js: ^6.3.7
-      vue: ^3.2.29
-
   '@simonwep/pickr@1.9.0':
     resolution: {integrity: sha512-oEYvv15PyfZzjoAzvXYt3UyNGwzsrpFxLaZKzkOSd0WYBVwLd19iJerePDONxC1iF6+DpcswPdLIM2KzCJuYFg==}
 
@@ -5052,11 +5042,6 @@ snapshots:
 
   '@scarf/scarf@1.4.0': {}
 
-  '@silverwind/vue3-calendar-heatmap@2.1.1(tippy.js@6.3.7)(vue@3.5.32(typescript@6.0.2))':
-    dependencies:
-      tippy.js: 6.3.7
-      vue: 3.5.32(typescript@6.0.2)
-
   '@simonwep/pickr@1.9.0':
     dependencies:
       core-js: 3.32.2
diff --git a/tests/e2e/heatmap.test.ts b/tests/e2e/heatmap.test.ts
new file mode 100644
index 00000000000..5aabfab196c
--- /dev/null
+++ b/tests/e2e/heatmap.test.ts
@@ -0,0 +1,9 @@
+import {test, expect} from '@playwright/test';
+import {login} from './utils.ts';
+
+test('heatmap tooltip shows on hover', async ({page}) => {
+  await login(page);
+  await page.goto('/');
+  await page.locator('.heatmap-day').first().hover();
+  await expect(page.locator('.tippy-box[data-state="visible"]')).toBeVisible();
+});
diff --git a/web_src/css/features/heatmap.css b/web_src/css/features/heatmap.css
index e40adf1fe48..a2d8c4ea590 100644
--- a/web_src/css/features/heatmap.css
+++ b/web_src/css/features/heatmap.css
@@ -32,26 +32,29 @@
   fill: currentcolor !important;
 }
 
-/* root legend */
-#user-heatmap .vch__container > .vch__legend {
+#user-heatmap .heatmap-footer {
   display: flex;
   font-size: 11px;
   justify-content: space-between;
 }
 
-/* for the "Less" and "More" legend */
-#user-heatmap .vch__legend .vch__legend {
+/* "Less [colors] More" scale */
+#user-heatmap .heatmap-legend {
   display: flex;
   align-items: center;
   justify-content: right;
 }
 
-#user-heatmap .vch__legend .vch__legend div:first-child,
-#user-heatmap .vch__legend .vch__legend div:last-child {
+#user-heatmap .heatmap-legend-svg {
+  margin-right: -12px;
+}
+
+#user-heatmap .heatmap-legend > div:first-child,
+#user-heatmap .heatmap-legend > div:last-child {
   display: inline-block;
   padding: 0 5px;
 }
 
-#user-heatmap .vch__day__square:hover {
+#user-heatmap .heatmap-day:hover {
   outline: 1.5px solid var(--color-text);
 }
diff --git a/web_src/js/components/ActivityHeatmap.vue b/web_src/js/components/ActivityHeatmap.vue
index 7c7e0cd94ca..08c590aa16b 100644
--- a/web_src/js/components/ActivityHeatmap.vue
+++ b/web_src/js/components/ActivityHeatmap.vue
@@ -1,21 +1,23 @@
 <script lang="ts" setup>
-// TODO: Switch to upstream after https://github.com/razorness/vue3-calendar-heatmap/pull/34 is merged
-import {CalendarHeatmap} from '@silverwind/vue3-calendar-heatmap';
-import {onMounted, shallowRef} from 'vue';
-import type {Value as HeatmapValue, Locale as HeatmapLocale} from '@silverwind/vue3-calendar-heatmap';
+import {computed, onBeforeUnmount, onMounted} from 'vue';
+import tippy, {createSingleton} from 'tippy.js';
+import type {CreateSingletonInstance, Instance} from 'tippy.js';
 
-defineProps<{
+type HeatmapValue = {date: Date; count: number};
+type HeatmapCell = {date: Date; colorIndex: number; ariaLabel: string; tooltip: string};
+type MonthLabel = {monthIdx: number; weekIdx: number};
+
+const props = defineProps<{
   values: HeatmapValue[];
   locale: {
     textTotalContributions: string;
-    heatMapLocale: Partial<HeatmapLocale>;
+    heatMapLocale: {months: string[]; days: string[]; on: string; more: string; less: string};
     noDataText: string;
     tooltipUnit: string;
   };
 }>();
 
 const colorRange = [
-  'var(--color-secondary-alpha-60)',
   'var(--color-secondary-alpha-60)',
   'var(--color-primary-light-4)',
   'var(--color-primary-light-2)',
@@ -24,21 +26,112 @@ const colorRange = [
   'var(--color-primary-dark-4)',
 ];
 
-const endDate = shallowRef(new Date());
+const squareSize = 10;
+const squareBorder = 2;
+const cellSize = squareSize + squareBorder;
+const daysInWeek = 7;
+const trailingDays = 365;
+const gridLeft = Math.ceil(squareSize * 2.5);
+const gridTop = squareSize + squareSize / 2;
 
-onMounted(() => {
-  // work around issue with first legend color being rendered twice and legend cut off
-  const legend = document.querySelector<HTMLElement>('.vch__external-legend-wrapper')!;
-  legend.setAttribute('viewBox', '12 0 80 10');
-  legend.style.marginRight = '-12px';
+const now = new Date();
+
+function dateKey(d: Date): string {
+  return `${d.getFullYear()}${String(d.getMonth()).padStart(2, '0')}${String(d.getDate()).padStart(2, '0')}`;
+}
+
+function shiftDate(d: Date, days: number): Date {
+  const out = new Date(d);
+  out.setDate(out.getDate() + days);
+  return out;
+}
+
+const grid = computed(() => {
+  const start = shiftDate(now, -trailingDays);
+  const padStart = start.getDay();
+  const padEnd = daysInWeek - 1 - now.getDay();
+  const weekCount = (trailingDays + 1 + padStart + padEnd) / daysInWeek;
+
+  const maxCount = props.values.length ? Math.max(...props.values.map((v) => v.count)) : 0;
+  const max = maxCount > 0 ? Math.ceil(maxCount / 5 * 4) : 1;
+
+  const activities = new Map<string, {count: number; colorIndex: number}>();
+  for (const {date, count} of props.values) {
+    const colorIndex = count >= max ? 4 : Math.max(1, Math.ceil((count / max) * 3));
+    activities.set(dateKey(date), {count, colorIndex});
+  }
+
+  const {months, on} = props.locale.heatMapLocale;
+  const {noDataText, tooltipUnit} = props.locale;
+
+  const cursorStart = shiftDate(start, -padStart);
+  const cursor = new Date(cursorStart.getFullYear(), cursorStart.getMonth(), cursorStart.getDate());
+  const calendar: HeatmapCell[][] = [];
+  for (let w = 0; w < weekCount; w++) {
+    const week: HeatmapCell[] = [];
+    for (let d = 0; d < daysInWeek; d++) {
+      const hit = activities.get(dateKey(cursor));
+      const dateStr = `${months[cursor.getMonth()]} ${cursor.getDate()}, ${cursor.getFullYear()}`;
+      const head = hit ? `${hit.count} ${tooltipUnit}` : noDataText;
+      week.push({
+        date: new Date(cursor),
+        colorIndex: hit ? hit.colorIndex : 0,
+        ariaLabel: `${head} ${on} ${dateStr}`,
+        tooltip: `<b>${head}</b> ${on} ${dateStr}`,
+      });
+      cursor.setDate(cursor.getDate() + 1);
+    }
+    calendar.push(week);
+  }
+
+  const monthLabels: MonthLabel[] = [];
+  for (let w = 1; w < calendar.length; w++) {
+    const prev = calendar[w - 1][0].date;
+    const curr = calendar[w][0].date;
+    if (prev.getMonth() !== curr.getMonth()) {
+      monthLabels.push({monthIdx: curr.getMonth(), weekIdx: w});
+    }
+  }
+
+  const width = gridLeft + (cellSize * weekCount) + squareBorder;
+  const height = gridTop + (cellSize * daysInWeek);
+  return {calendar, monthLabels, width, height};
 });
 
-function handleDayClick(e: Event & {date: Date}) {
-  // Reset filter if same date is clicked
+const legendViewBox = `${cellSize} 0 ${squareSize * (colorRange.length + 2)} ${squareSize}`;
+
+const cellInstances = new Map<Element, Instance>();
+let singleton: CreateSingletonInstance | null = null;
+
+onMounted(() => {
+  singleton = createSingleton([], {
+    overrides: [],
+    moveTransition: 'transform 0.1s ease-out',
+    allowHTML: true,
+    theme: 'tooltip',
+    role: 'tooltip',
+    placement: 'top',
+  });
+});
+
+onBeforeUnmount(() => {
+  singleton?.destroy();
+  for (const instance of cellInstances.values()) instance.destroy();
+  cellInstances.clear();
+});
+
+function lazyInitTooltip(e: MouseEvent) {
+  const el = e.target as Element;
+  if (!singleton || cellInstances.has(el) || !el.classList.contains('heatmap-day')) return;
+  cellInstances.set(el, tippy(el, {content: el.getAttribute('data-tooltip')!}));
+  singleton.setInstances([...cellInstances.values()]);
+}
+
+function handleDayClick(date: Date) {
   const params = new URLSearchParams(document.location.search);
   const queryDate = params.get('date');
   // Timezone has to be stripped because toISOString() converts to UTC
-  const clickedDate = new Date(e.date.getTime() - (e.date.getTimezoneOffset() * 60000)).toISOString().substring(0, 10);
+  const clickedDate = new Date(date.getTime() - (date.getTimezoneOffset() * 60000)).toISOString().substring(0, 10);
 
   if (queryDate && queryDate === clickedDate) {
     params.delete('date');
@@ -53,16 +146,63 @@ function handleDayClick(e: Event & {date: Date}) {
 }
 </script>
 <template>
-  <calendar-heatmap
-    :locale="locale.heatMapLocale"
-    :no-data-text="locale.noDataText"
-    :tooltip-unit="locale.tooltipUnit"
-    :end-date="endDate"
-    :values="values"
-    :range-color="colorRange"
-    @day-click="handleDayClick($event)"
-    :tippy-props="{theme: 'tooltip'}"
-  >
-    <template #vch__legend-left>{{ locale.textTotalContributions }}</template>
-  </calendar-heatmap>
+  <div>
+    <svg class="heatmap-svg" :viewBox="`0 0 ${grid.width} ${grid.height}`">
+      <g class="heatmap-month-labels" :transform="`translate(${gridLeft}, 0)`">
+        <text
+          v-for="m in grid.monthLabels"
+          :key="m.weekIdx"
+          class="heatmap-month-label"
+          :x="cellSize * m.weekIdx"
+          :y="cellSize - squareBorder"
+        >
+          {{ locale.heatMapLocale.months[m.monthIdx] }}
+        </text>
+      </g>
+      <g class="heatmap-day-labels" :transform="`translate(0, ${gridTop})`">
+        <text class="heatmap-day-label" :x="0" :y="20">{{ locale.heatMapLocale.days[1] }}</text>
+        <text class="heatmap-day-label" :x="0" :y="44">{{ locale.heatMapLocale.days[3] }}</text>
+        <text class="heatmap-day-label" :x="0" :y="69">{{ locale.heatMapLocale.days[5] }}</text>
+      </g>
+      <g class="heatmap-grid" :transform="`translate(${gridLeft}, ${gridTop})`" @mouseover="lazyInitTooltip">
+        <g
+          v-for="(week, w) in grid.calendar"
+          :key="w"
+          class="heatmap-week"
+          :transform="`translate(${w * cellSize}, 0)`"
+        >
+          <template v-for="(day, d) in week" :key="d">
+            <rect
+              v-if="day.date < now"
+              class="heatmap-day"
+              :transform="`translate(0, ${d * cellSize})`"
+              :width="squareSize"
+              :height="squareSize"
+              :style="{fill: colorRange[day.colorIndex]}"
+              :aria-label="day.ariaLabel"
+              :data-tooltip="day.tooltip"
+              @click="handleDayClick(day.date)"
+            />
+          </template>
+        </g>
+      </g>
+    </svg>
+    <div class="heatmap-footer">
+      <div>{{ locale.textTotalContributions }}</div>
+      <div class="heatmap-legend">
+        <div>{{ locale.heatMapLocale.less }}</div>
+        <svg class="heatmap-legend-svg" :viewBox="legendViewBox" :height="squareSize">
+          <rect
+            v-for="(color, i) in colorRange"
+            :key="i"
+            :width="squareSize"
+            :height="squareSize"
+            :x="(i + 1) * cellSize"
+            :style="{fill: color}"
+          />
+        </svg>
+        <div>{{ locale.heatMapLocale.more }}</div>
+      </div>
+    </div>
+  </div>
 </template>