diff --git a/frontend/src/components/License/LicenseManager.css b/frontend/src/components/License/LicenseManager.css
new file mode 100644
index 0000000..4ed2008
--- /dev/null
+++ b/frontend/src/components/License/LicenseManager.css
@@ -0,0 +1,266 @@
+.license-manager {
+    min-height: 100vh;
+    background-color: #f5f5f7;
+}
+
+.lm-body {
+    padding: 20px;
+    max-width: 800px;
+    margin: 0 auto;
+}
+
+.lm-loading,
+.lm-empty {
+    padding: 24px;
+    text-align: center;
+    color: #999;
+    font-style: italic;
+}
+
+.lm-toolbar {
+    margin-bottom: 16px;
+}
+
+.lm-back {
+    padding: 6px 12px;
+    background: white;
+    border: 1px solid #ddd;
+    border-radius: 6px;
+    color: #666;
+    cursor: pointer;
+    font-size: 13px;
+}
+
+.lm-back:hover {
+    border-color: #667eea;
+    color: #667eea;
+}
+
+.lm-ok,
+.lm-error {
+    padding: 8px 12px;
+    border-radius: 6px;
+    font-size: 13px;
+    margin-bottom: 12px;
+}
+
+.lm-ok {
+    background-color: #e8f5e9;
+    border: 1px solid #c8e6c9;
+    color: #2e7d32;
+}
+
+.lm-error {
+    background-color: #fee;
+    border: 1px solid #fcc;
+    color: #c33;
+}
+
+.lm-panel {
+    background: white;
+    border-radius: 8px;
+    padding: 18px;
+    margin-bottom: 16px;
+    box-shadow: 0 1px 3px rgba(0, 0, 0, 0.08);
+}
+
+.lm-panel h3 {
+    margin: 0 0 12px 0;
+    font-size: 12px;
+    font-weight: 600;
+    color: #888;
+    text-transform: uppercase;
+    letter-spacing: 0.5px;
+}
+
+.lm-badge {
+    display: inline-block;
+    padding: 3px 10px;
+    border-radius: 4px;
+    font-size: 11px;
+    font-weight: 600;
+    text-transform: uppercase;
+    letter-spacing: 0.5px;
+    margin-bottom: 10px;
+}
+
+.lm-badge--ok {
+    background-color: #e8f5e9;
+    color: #2e7d32;
+}
+
+.lm-badge--warn {
+    background-color: #fff3cd;
+    color: #856404;
+}
+
+.lm-facts {
+    display: grid;
+    grid-template-columns: 140px 1fr;
+    gap: 6px 12px;
+    margin: 0;
+}
+
+.lm-facts dt {
+    font-size: 11px;
+    font-weight: 600;
+    color: #888;
+    text-transform: uppercase;
+    letter-spacing: 0.5px;
+    align-self: center;
+}
+
+.lm-facts dd {
+    margin: 0;
+    font-size: 14px;
+    color: #333;
+}
+
+.lm-reason {
+    margin: 0 0 8px 0;
+    font-size: 14px;
+    color: #333;
+}
+
+.lm-grace {
+    margin: 0;
+    font-size: 13px;
+    color: #666;
+    line-height: 1.5;
+}
+
+.lm-hint {
+    margin: 0 0 12px 0;
+    font-size: 13px;
+    color: #666;
+    line-height: 1.5;
+}
+
+.lm-fingerprint {
+    display: flex;
+    align-items: center;
+    gap: 8px;
+}
+
+.lm-fingerprint code {
+    flex: 1;
+    padding: 10px 12px;
+    background-color: #f8f9fa;
+    border: 1px solid #dee2e6;
+    border-radius: 6px;
+    font-family: 'Courier New', monospace;
+    font-size: 18px;
+    letter-spacing: 1px;
+    color: #333;
+    word-break: break-all;
+}
+
+.lm-components {
+    font-size: 11px !important;
+    letter-spacing: 0 !important;
+}
+
+.lm-fingerprint button {
+    padding: 8px 14px;
+    background: none;
+    border: 1px solid #ddd;
+    border-radius: 6px;
+    color: #666;
+    font-size: 13px;
+    cursor: pointer;
+    flex-shrink: 0;
+}
+
+.lm-fingerprint button:hover {
+    border-color: #667eea;
+    color: #667eea;
+}
+
+.lm-details {
+    margin-top: 10px;
+}
+
+.lm-details summary {
+    font-size: 12px;
+    color: #888;
+    cursor: pointer;
+    margin-bottom: 8px;
+}
+
+.lm-blob {
+    width: 100%;
+    padding: 10px;
+    border: 1px solid #ddd;
+    border-radius: 6px;
+    font-family: 'Courier New', monospace;
+    font-size: 12px;
+    box-sizing: border-box;
+    resize: vertical;
+}
+
+.lm-install {
+    margin-top: 10px;
+    padding: 9px 18px;
+    background: linear-gradient(135deg, #667eea, #764ba2);
+    border: none;
+    border-radius: 6px;
+    color: white;
+    font-size: 13px;
+    font-weight: 600;
+    cursor: pointer;
+}
+
+.lm-install:hover:not(:disabled) {
+    transform: translateY(-1px);
+    box-shadow: 0 3px 8px rgba(102, 126, 234, 0.4);
+}
+
+.lm-install:disabled {
+    opacity: 0.5;
+    cursor: not-allowed;
+}
+
+.lm-table {
+    width: 100%;
+    border-collapse: collapse;
+}
+
+.lm-table th {
+    padding: 0.5rem 0.75rem;
+    text-align: left;
+    font-weight: 600;
+    color: #495057;
+    font-size: 0.75rem;
+    border-bottom: 2px solid #dee2e6;
+    text-transform: uppercase;
+    letter-spacing: 0.3px;
+    background-color: #f8f9fa;
+}
+
+.lm-table td {
+    padding: 0.5rem 0.75rem;
+    border-bottom: 1px solid #dee2e6;
+    font-size: 0.85rem;
+    color: #333;
+    font-family: 'Courier New', monospace;
+}
+
+/* Persistent, non-dismissible banner shown app-wide during grace */
+.license-banner {
+    padding: 8px 16px;
+    background-color: #fff3cd;
+    border-bottom: 1px solid #ffe69c;
+    color: #856404;
+    font-size: 13px;
+    text-align: center;
+}
+
+.license-banner strong {
+    font-weight: 600;
+}
+
+.license-banner--blocked {
+    background-color: #fee;
+    border-bottom-color: #fcc;
+    color: #c33;
+}
diff --git a/frontend/src/components/License/LicenseManager.jsx b/frontend/src/components/License/LicenseManager.jsx
new file mode 100644
index 0000000..0457ea0
--- /dev/null
+++ b/frontend/src/components/License/LicenseManager.jsx
@@ -0,0 +1,167 @@
+import { useState } from 'react';
+import { useNavigate } from 'react-router-dom';
+import Header from '../Header';
+import { useLicense } from '../../contexts/LicenseContext';
+import api from '../../services/api';
+import './LicenseManager.css';
+
+export default function LicenseManager() {
+    const navigate = useNavigate();
+    const { status, refreshStatus } = useLicense();
+
+    const [blob, setBlob] = useState('');
+    const [message, setMessage] = useState('');
+    const [error, setError] = useState('');
+    const [saving, setSaving] = useState(false);
+    const [copied, setCopied] = useState('');
+
+    const copy = (text, label) => {
+        navigator.clipboard?.writeText(text).then(
+            () => { setCopied(label); setTimeout(() => setCopied(''), 2000); },
+            () => setError('Could not copy - select and copy manually')
+        );
+    };
+
+    const handleInstall = async () => {
+        if (!blob.trim()) return;
+        setSaving(true); setError(''); setMessage('');
+        try {
+            await api.post('/api/license/', { key_blob: blob.trim() });
+            await refreshStatus();
+            setBlob('');
+            setMessage('Licence installed.');
+        } catch (err) {
+            setError(err.response?.data?.detail || 'Could not install licence');
+        } finally {
+            setSaving(false);
+        }
+    };
+
+    if (!status) {
+        return (
+            <div className="license-manager">
+                <Header />
+                <div className="lm-body"><div className="lm-loading">Loading licence...</div></div>
+            </div>
+        );
+    }
+
+    const componentsJson = JSON.stringify(status.components || {});
+
+    return (
+        <div className="license-manager">
+            <Header />
+            <div className="lm-body">
+                <div className="lm-toolbar">
+                    <button className="lm-back" onClick={() => navigate('/')}>&larr; Back</button>
+                </div>
+
+                {message && <div className="lm-ok">{message}</div>}
+                {error && <div className="lm-error">{error}</div>}
+
+                {/* Current state */}
+                <div className="lm-panel">
+                    <h3>Licence</h3>
+                    {status.valid ? (
+                        <div className="lm-state lm-state--ok">
+                            <div className="lm-badge lm-badge--ok">Licensed</div>
+                            <dl className="lm-facts">
+                                <dt>Customer</dt><dd>{status.customer || '—'}</dd>
+                                <dt>Stations</dt>
+                                <dd>{status.stations_used} of {status.stations} in use</dd>
+                            </dl>
+                        </div>
+                    ) : (
+                        <div className="lm-state lm-state--warn">
+                            <div className="lm-badge lm-badge--warn">
+                                {status.in_grace ? 'Not licensed' : 'Licence expired'}
+                            </div>
+                            <p className="lm-reason">{status.reason}</p>
+                            {status.in_grace ? (
+                                <p className="lm-grace">
+                                    Everything keeps working for <strong>{status.grace_days_left} more days</strong>.
+                                    After that only {1} station can measure. Send the fingerprint below to
+                                    your supplier to get a licence key.
+                                </p>
+                            ) : (
+                                <p className="lm-grace">
+                                    The grace period has ended, so only {status.stations} station can measure.
+                                    Send the fingerprint below to your supplier.
+                                </p>
+                            )}
+                        </div>
+                    )}
+                </div>
+
+                {/* Fingerprint to send */}
+                <div className="lm-panel">
+                    <h3>This machine</h3>
+                    <p className="lm-hint">
+                        Send this to your supplier to obtain a licence key. It identifies this
+                        server only &mdash; the values are one-way hashes, not hardware serial numbers.
+                    </p>
+
+                    <div className="lm-fingerprint">
+                        <code>{status.fingerprint}</code>
+                        <button onClick={() => copy(status.fingerprint, 'fingerprint')}>
+                            {copied === 'fingerprint' ? 'Copied' : 'Copy'}
+                        </button>
+                    </div>
+
+                    <details className="lm-details">
+                        <summary>Full details (needed to issue the key)</summary>
+                        <div className="lm-fingerprint">
+                            <code className="lm-components">{componentsJson}</code>
+                            <button onClick={() => copy(componentsJson, 'components')}>
+                                {copied === 'components' ? 'Copied' : 'Copy'}
+                            </button>
+                        </div>
+                    </details>
+                </div>
+
+                {/* Install */}
+                <div className="lm-panel">
+                    <h3>Install a licence key</h3>
+                    <textarea
+                        className="lm-blob"
+                        value={blob}
+                        onChange={e => setBlob(e.target.value)}
+                        placeholder="Paste the licence key from your supplier"
+                        rows={5}
+                    />
+                    <button className="lm-install" onClick={handleInstall} disabled={saving || !blob.trim()}>
+                        {saving ? 'Checking...' : 'Install licence'}
+                    </button>
+                </div>
+
+                {/* Connected stations */}
+                {status.slots && (
+                    <div className="lm-panel">
+                        <h3>Connected stations ({status.slots.length})</h3>
+                        {status.slots.length === 0 ? (
+                            <div className="lm-empty">No stations have reported in.</div>
+                        ) : (
+                            <table className="lm-table">
+                                <thead>
+                                    <tr>
+                                        <th>Station</th><th>COM port</th><th>Bridge version</th><th>Last seen</th>
+                                    </tr>
+                                </thead>
+                                <tbody>
+                                    {status.slots.map(s => (
+                                        <tr key={s.station_key}>
+                                            <td>{s.station_key}</td>
+                                            <td>{s.com_port || '—'}</td>
+                                            <td>{s.bridge_version || '—'}</td>
+                                            <td>{new Date(s.last_seen).toLocaleTimeString()}</td>
+                                        </tr>
+                                    ))}
+                                </tbody>
+                            </table>
+                        )}
+                    </div>
+                )}
+            </div>
+        </div>
+    );
+}
diff --git a/frontend/src/contexts/LicenseContext.jsx b/frontend/src/contexts/LicenseContext.jsx
new file mode 100644
index 0000000..5d5ea2a
--- /dev/null
+++ b/frontend/src/contexts/LicenseContext.jsx
@@ -0,0 +1,109 @@
+import { createContext, useContext, useState, useEffect, useCallback, useRef } from 'react';
+import api from '../services/api';
+
+const LicenseContext = createContext(null);
+
+const SERIAL_URL = process.env.REACT_APP_SERIAL_URL || 'http://localhost:5000';
+const HEARTBEAT_MS = 30000;   // server releases a slot after 120s, so 4 missed beats
+
+export const useLicense = () => {
+    const ctx = useContext(LicenseContext);
+    if (!ctx) throw new Error('useLicense must be used within LicenseProvider');
+    return ctx;
+};
+
+/** Stable identifier for the bridge this browser is using.
+ *
+ *  The bridge deliberately never talks to Django, so the browser reports which
+ *  station it is on. Built from the bridge address plus its COM port, so two
+ *  browsers on the same station share one slot rather than consuming two.
+ */
+async function readStationKey() {
+    try {
+        const res = await fetch(`${SERIAL_URL}/status`);
+        if (!res.ok) return null;
+        const status = await res.json();
+        const raw = `${SERIAL_URL}|${status.com_port || 'unknown'}`;
+        // Short stable hash - this is an identifier, not a secret
+        let hash = 0;
+        for (let i = 0; i < raw.length; i++) {
+            hash = ((hash << 5) - hash + raw.charCodeAt(i)) | 0;
+        }
+        return {
+            station_key: `st-${Math.abs(hash).toString(36)}`,
+            com_port: status.com_port || '',
+            bridge_version: status.version || '',
+        };
+    } catch {
+        return null;
+    }
+}
+
+export function LicenseProvider({ children }) {
+    const [state, setState] = useState({
+        allowed: true,          // assume allowed until told otherwise, so a slow
+        stationsUsed: null,     // first heartbeat never blocks a working station
+        stationsLicensed: null,
+        detail: null,
+        stationKey: null,
+    });
+    const [status, setStatus] = useState(null);
+
+    const stationRef = useRef(null);
+
+    const beat = useCallback(async () => {
+        if (!stationRef.current) {
+            stationRef.current = await readStationKey();
+        }
+        const station = stationRef.current;
+        if (!station) return;   // bridge unreachable; nothing to register
+
+        try {
+            const res = await api.post('/api/license/heartbeat/', station);
+            setState({
+                allowed: res.data.allowed,
+                stationsUsed: res.data.stations_used,
+                stationsLicensed: res.data.stations_licensed,
+                detail: null,
+                stationKey: station.station_key,
+            });
+        } catch (err) {
+            if (err.response?.status === 403) {
+                const d = err.response.data || {};
+                setState({
+                    allowed: false,
+                    stationsUsed: d.stations_used ?? null,
+                    stationsLicensed: d.stations_licensed ?? null,
+                    detail: d.detail || 'Licence limit reached',
+                    stationKey: station.station_key,
+                });
+            }
+            // Other failures (server down) leave the previous state alone -
+            // a licence check must not stop a working weighbridge.
+        }
+    }, []);
+
+    useEffect(() => {
+        beat();
+        const timer = setInterval(beat, HEARTBEAT_MS);
+        return () => clearInterval(timer);
+    }, [beat]);
+
+    const loadStatus = useCallback(async () => {
+        try {
+            const res = await api.get('/api/license/');
+            setStatus(res.data);
+            return res.data;
+        } catch {
+            return null;
+        }
+    }, []);
+
+    useEffect(() => { loadStatus(); }, [loadStatus]);
+
+    return (
+        <LicenseContext.Provider value={{ ...state, status, refreshStatus: loadStatus }}>
+            {children}
+        </LicenseContext.Provider>
+    );
+}
diff --git a/tools/license_tool.py b/tools/license_tool.py
new file mode 100644
index 0000000..b54ac2b
--- /dev/null
+++ b/tools/license_tool.py
@@ -0,0 +1,141 @@
+"""Vendor licence signing tool - KEEP THIS AND THE PRIVATE KEY OUT OF CUSTOMER BUILDS.
+
+This is the only thing that can create a valid licence. The application can only
+verify. If the private key leaks, every licence ever issued becomes forgeable and
+it cannot be rotated without reissuing to every customer, because the public key
+is compiled into shipped binaries.
+
+Usage:
+
+  Create your keypair once:
+      python license_tool.py keygen
+
+  Then for each customer, from the fingerprint and components they send you:
+      python license_tool.py sign --customer "Port of Varna" --stations 5 \\
+          --components '{"board":"ab12...","disk":"cd34...","mac":"ef56...","guid":"78ab..."}'
+
+The customer reads their component hashes from the admin licence screen (there is
+a copy button) - they are hashes, not raw serial numbers, so they carry no
+identifying hardware detail.
+"""
+
+import argparse
+import base64
+import json
+import os
+import sys
+
+from cryptography.hazmat.primitives.asymmetric.ed25519 import (
+    Ed25519PrivateKey, Ed25519PublicKey,
+)
+from cryptography.hazmat.primitives import serialization
+
+KEY_PATH = os.path.join(os.path.dirname(os.path.abspath(__file__)), 'license_private.key')
+
+
+def keygen(args):
+    if os.path.exists(KEY_PATH) and not args.force:
+        print(f"Refusing to overwrite {KEY_PATH}")
+        print("Every licence signed with the existing key would stop verifying.")
+        print("Pass --force only if you are certain.")
+        return 1
+
+    private_key = Ed25519PrivateKey.generate()
+    raw = private_key.private_bytes(
+        encoding=serialization.Encoding.Raw,
+        format=serialization.PrivateFormat.Raw,
+        encryption_algorithm=serialization.NoEncryption(),
+    )
+    with open(KEY_PATH, 'wb') as fh:
+        fh.write(base64.b64encode(raw))
+
+    public_raw = private_key.public_key().public_bytes(
+        encoding=serialization.Encoding.Raw,
+        format=serialization.PublicFormat.Raw,
+    )
+    public_b64 = base64.b64encode(public_raw).decode()
+
+    print(f"Private key written to {KEY_PATH}")
+    print("  Back this up somewhere safe. It cannot be recovered.")
+    print("  Never commit it, never ship it.\n")
+    print("Put this public key in backend/api/licensing.py as LICENSE_PUBLIC_KEY:\n")
+    print(f"LICENSE_PUBLIC_KEY = '{public_b64}'")
+    return 0
+
+
+def _load_private_key():
+    if not os.path.exists(KEY_PATH):
+        print(f"No private key at {KEY_PATH} - run 'keygen' first.")
+        sys.exit(1)
+    with open(KEY_PATH, 'rb') as fh:
+        return Ed25519PrivateKey.from_private_bytes(base64.b64decode(fh.read()))
+
+
+def sign(args):
+    private_key = _load_private_key()
+
+    try:
+        components = json.loads(args.components)
+    except json.JSONDecodeError as exc:
+        print(f"--components is not valid JSON: {exc}")
+        return 1
+
+    known = {'board', 'disk', 'mac', 'guid'}
+    unknown = set(components) - known
+    if unknown:
+        print(f"Unknown component keys: {sorted(unknown)} (expected {sorted(known)})")
+        return 1
+    present = [k for k, v in components.items() if v]
+    if len(present) < 3:
+        print(f"Only {len(present)} components supplied; at least 3 must match on the")
+        print("customer machine, so signing this licence would lock them out.")
+        return 1
+
+    payload = {
+        'customer': args.customer,
+        'stations': args.stations,
+        'components': components,
+    }
+    if args.expires:
+        payload['expires'] = args.expires
+
+    payload_json = json.dumps(payload, sort_keys=True, separators=(',', ':'))
+    signature = private_key.sign(payload_json.encode('utf-8'))
+    blob = base64.b64encode(
+        f"{payload_json}.{base64.b64encode(signature).decode()}".encode('utf-8')
+    ).decode()
+
+    print(f"Licence for {args.customer}, {args.stations} station(s)")
+    print(f"Components supplied: {', '.join(sorted(present))}")
+    if args.expires:
+        print(f"Expires: {args.expires}")
+    else:
+        print("Perpetual (no expiry)")
+    print("\nSend this to the customer:\n")
+    print(blob)
+    return 0
+
+
+def main():
+    parser = argparse.ArgumentParser(description=__doc__)
+    sub = parser.add_subparsers(dest='command', required=True)
+
+    p_keygen = sub.add_parser('keygen', help='Create the vendor keypair (once)')
+    p_keygen.add_argument('--force', action='store_true')
+    p_keygen.set_defaults(func=keygen)
+
+    p_sign = sub.add_parser('sign', help='Sign a licence for a customer machine')
+    p_sign.add_argument('--customer', required=True)
+    p_sign.add_argument('--stations', type=int, required=True)
+    p_sign.add_argument('--components', required=True,
+                        help='JSON of hashed components from the admin screen')
+    p_sign.add_argument('--expires', default=None,
+                        help='ISO date, e.g. 2027-01-01T00:00:00+00:00 (omit for perpetual)')
+    p_sign.set_defaults(func=sign)
+
+    args = parser.parse_args()
+    sys.exit(args.func(args))
+
+
+if __name__ == '__main__':
+    main()