diff --git a/nextjs-app/__tests__/components/MetricTooltip.test.tsx b/nextjs-app/__tests__/components/MetricTooltip.test.tsx
new file mode 100644
index 0000000..7c6c191
--- /dev/null
+++ b/nextjs-app/__tests__/components/MetricTooltip.test.tsx
@@ -0,0 +1,32 @@
+import { render, screen } from '@testing-library/react';
+import userEvent from '@testing-library/user-event';
+import { MetricTooltip } from '@/components/MetricTooltip';
+import { METRIC_EXPLANATIONS } from '@/lib/metrics';
+
+describe('MetricTooltip', () => {
+  it('resolves content from a metricKey', async () => {
+    const key = Object.keys(METRIC_EXPLANATIONS)[0];
+    const exp = METRIC_EXPLANATIONS[key];
+    const user = userEvent.setup();
+    render(<MetricTooltip metricKey={key} />);
+    // Collapsed by default — the popover content is not in the DOM until opened
+    // (the old component left an always-present role="tooltip" span behind).
+    expect(screen.queryByRole('tooltip')).not.toBeInTheDocument();
+    await user.click(screen.getByRole('button', { name: `What does ${exp.label} mean?` }));
+    const tip = await screen.findByRole('tooltip');
+    expect(tip).toHaveTextContent(exp.plain);
+  });
+
+  it('renders nothing for an unknown metricKey with no explicit content', () => {
+    const { container } = render(<MetricTooltip metricKey="__nope__" />);
+    expect(container).toBeEmptyDOMElement();
+  });
+
+  it('lets explicit props override the looked-up explanation', async () => {
+    const key = Object.keys(METRIC_EXPLANATIONS)[0];
+    const user = userEvent.setup();
+    render(<MetricTooltip metricKey={key} plain="custom text" />);
+    await user.click(screen.getByRole('button'));
+    expect(await screen.findByRole('tooltip')).toHaveTextContent('custom text');
+  });
+});
diff --git a/nextjs-app/components/MetricTooltip.module.css b/nextjs-app/components/MetricTooltip.module.css
deleted file mode 100644
index ccf0801..0000000
--- a/nextjs-app/components/MetricTooltip.module.css
+++ /dev/null
@@ -1,114 +0,0 @@
-.wrapper {
-  position: relative;
-  display: inline-flex;
-  align-items: center;
-  margin-left: 0.3em;
-}
-
-.icon {
-  /* A real button: 24px tap target (WCAG 2.5.8) drawn as the small glyph. */
-  display: inline-flex;
-  align-items: center;
-  justify-content: center;
-  min-width: 24px;
-  min-height: 24px;
-  margin: -6px 0;
-  padding: 0;
-  border: none;
-  background: none;
-  font-size: 0.9em;
-  color: var(--text-muted, #8a7a72);
-  cursor: help;
-  line-height: 1;
-  user-select: none;
-  transition: color 0.15s ease;
-}
-
-.wrapper:hover .icon,
-.icon[aria-expanded="true"] {
-  color: var(--accent-coral-dark, #b04a2e);
-}
-
-.tooltip {
-  visibility: hidden;
-  opacity: 0;
-  position: absolute;
-  bottom: calc(100% + 6px);
-  left: 50%;
-  transform: translateX(-50%);
-  z-index: 9999;
-  width: 220px;
-  background: var(--bg-primary, #faf7f2);
-  border: 1px solid var(--border-color, #e8ddd4);
-  border-radius: 10px;
-  box-shadow: 0 4px 16px rgba(44, 36, 32, 0.15);
-  padding: 0.6rem 0.75rem;
-  display: flex;
-  flex-direction: column;
-  gap: 0.3rem;
-  pointer-events: none;
-  transition: opacity 0.15s ease, visibility 0.15s ease;
-}
-
-/* Reveal on hover (desktop), keyboard focus, or explicit tap/click toggle. */
-.wrapper:hover .tooltip,
-.wrapper:focus-within .tooltip,
-.tooltipOpen {
-  visibility: visible;
-  opacity: 1;
-}
-
-.tooltipOpen {
-  pointer-events: auto;
-}
-
-/* Small arrow pointing down */
-.tooltip::after {
-  content: '';
-  position: absolute;
-  top: 100%;
-  left: 50%;
-  transform: translateX(-50%);
-  border: 5px solid transparent;
-  border-top-color: var(--border-color, #e8ddd4);
-}
-
-.tooltipLabel {
-  font-weight: 600;
-  font-size: 0.75rem;
-  color: var(--text-primary, #2c2420);
-}
-
-.tooltipPlain {
-  font-size: 0.75rem;
-  color: var(--text-secondary, #5a4a44);
-  line-height: 1.4;
-}
-
-.tooltipDetail {
-  font-size: 0.7rem;
-  color: var(--text-muted, #8a7a72);
-  line-height: 1.4;
-  margin-top: 0.1rem;
-}
-
-@media (max-width: 480px) {
-  .tooltip {
-    width: 180px;
-  }
-}
-
-/* Anchor the bubble to open rightward on phones — icons follow their labels,
-   which start at the left edge, so centring pushed the bubble off-screen. */
-@media (max-width: 640px) {
-  .tooltip {
-    left: -12px;
-    right: auto;
-    transform: none;
-  }
-
-  .tooltip::after {
-    left: 16px;
-    transform: none;
-  }
-}
diff --git a/nextjs-app/components/MetricTooltip.tsx b/nextjs-app/components/MetricTooltip.tsx
index 6bef6f4..d27fc30 100644
--- a/nextjs-app/components/MetricTooltip.tsx
+++ b/nextjs-app/components/MetricTooltip.tsx
@@ -1,8 +1,7 @@
 'use client';
 
-import { useEffect, useRef, useState } from 'react';
 import { METRIC_EXPLANATIONS } from '@/lib/metrics';
-import styles from './MetricTooltip.module.css';
+import { InfoPopover } from './InfoPopover';
 
 interface MetricTooltipProps {
   metricKey?: string;
@@ -13,51 +12,13 @@ interface MetricTooltipProps {
 
 export function MetricTooltip({ metricKey, label, plain, detail }: MetricTooltipProps) {
   const explanation = metricKey ? METRIC_EXPLANATIONS[metricKey] : undefined;
-  const tooltipLabel = label ?? explanation?.label;
-  const tooltipPlain = plain ?? explanation?.plain;
-  const tooltipDetail = detail ?? explanation?.detail;
-
-  // Tap/click/keyboard toggle so the definition is reachable on touch devices
-  // and by keyboard, not just mouse hover (hover still works on desktop).
-  const [open, setOpen] = useState(false);
-  const wrapperRef = useRef<HTMLSpanElement>(null);
-
-  useEffect(() => {
-    if (!open) return;
-    const dismiss = (e: Event) => {
-      if (wrapperRef.current && e.target instanceof Node && !wrapperRef.current.contains(e.target)) {
-        setOpen(false);
-      }
-    };
-    const onKey = (e: KeyboardEvent) => {
-      if (e.key === 'Escape') setOpen(false);
-    };
-    document.addEventListener('click', dismiss);
-    document.addEventListener('keydown', onKey);
-    return () => {
-      document.removeEventListener('click', dismiss);
-      document.removeEventListener('keydown', onKey);
-    };
-  }, [open]);
-
-  if (!tooltipPlain) return null;
-
+  const resolvedLabel = label ?? explanation?.label;
   return (
-    <span className={styles.wrapper} ref={wrapperRef}>
-      <button
-        type="button"
-        className={styles.icon}
-        aria-expanded={open}
-        aria-label={`What does ${tooltipLabel ?? 'this metric'} mean?`}
-        onClick={() => setOpen((o) => !o)}
-      >
-        ⓘ
-      </button>
-      <span className={`${styles.tooltip}${open ? ` ${styles.tooltipOpen}` : ''}`} role="tooltip">
-        {tooltipLabel && <span className={styles.tooltipLabel}>{tooltipLabel}</span>}
-        <span className={styles.tooltipPlain}>{tooltipPlain}</span>
-        {tooltipDetail && <span className={styles.tooltipDetail}>{tooltipDetail}</span>}
-      </span>
-    </span>
+    <InfoPopover
+      label={resolvedLabel}
+      plain={plain ?? explanation?.plain}
+      detail={detail ?? explanation?.detail}
+      ariaLabel={resolvedLabel ? `What does ${resolvedLabel} mean?` : undefined}
+    />
   );
 }