Exclusivebeta

Lookalike `<mv-lookalike>`

Look-alike detection for everything that claims to be someone you trust: wrap emails, chat threads, forms or paste targets, give it your trusted identities (trusted="Acme Bank <acme-bank.com>, @stripe.com, @northwind, Payroll <DE89 3704 …>") and every link, sender, email address, @handle, package or user name, IBAN and wallet address in scope, including plain text and fields as you type or paste, is compared with them. It catches homoglyphs from a compact confusables table (a Cyrillic “а”, a digit “0” for an “o”, a capital “I” for an “l”, “rn” for “m”, full-width and accented letters), punycode, typos (extra, missing, swapped or replaced letters by weighted edit distance), added words (“acme-bank-secure.com”, lure words flagged), TLD swaps, brand-as-subdomain and “[email protected]” userinfo tricks, display names and link texts that claim a brand the real address doesn’t belong to, and wallet address poisoning (same head and tail, different middle). Suspicious items get a wavy underline and an inline flag button with words; its panel lays the suspicious string over the trusted one with each differing character highlighted and numbered, then explains every detail that doesn’t fit, one by one, in plain words (“The “а” here is Cyrillic (U+0430), not the Latin letter “a”.”), with a verdict tier (probably fine, looks like X, impersonates X) and actions: Go to the real X, Use the real value for fields, Continue anyway (cancelable mv-lookalike-proceed) and Report. Clicks on flagged links are intercepted with that confirmation, then replayed natively. The analysis is pure and DOM-free (compare(a, b), check(value, trusted), checkLink(href, text, trusted), also as MvLookalike.compare), so the same rules run on the server.

Category	Feedback
Type	Web Component (`<mv-lookalike>`)
Status	beta
Kit	Trust and privacy
Also installs	button
Keywords	exclusive, culture, phishing, spoofing, impersonation, homoglyph, confusables, punycode, idn, typosquatting, lookalike-domain, link-safety, email-security, sender-verification, display-name, iban, wallet, address-poisoning, edit-distance, diff, security, trust

When to use

An inbox, support desk or chat shows links and senders that could impersonate your brand, your bank or your vendors
A payout or wire form must catch a payee email, IBAN or wallet address that is one character off a saved one
Admins paste domains, package names or usernames into allowlists and a near miss would open a hole
A server check and the UI must explain a spoofed link with the same rules and the same wording

Avoid when

The problem is hidden characters inside a typed value (zero-width spaces, exotic spaces, bidi controls), not imitation of a known name → use Invisibles instead
There is no list of trusted identities to compare against: generic phishing detection needs a server-side reputation service
A critical form value just needs to be echoed back for confirmation before submitting → use Read Back instead

Install

node scripts/add.mjs lookalike --out ./src/marvelous

AI agent with the Marvelous UI MCP server: install_components({ slugs: ["lookalike"], target_dir: "<absolute path>/src/marvelous", framework: "react" }).

Files copied (dependencies included): tokens/tokens.css, core/base.css, core/dismiss.js, core/dom.js, core/element.js, core/position.js, components/lookalike/lookalike.js, components/lookalike/lookalike.css, components/button/button.css.

Usage

Quick start, the smallest working markup:

<mv-lookalike trusted="Acme Bank <acme-bank.com>">
  <p>Your card is locked. Unlock it at <a href="https://acme-bank-secure.com/login">acme-bank-secure.com</a>.</p>
</mv-lookalike>

Canonical markup, to start from and customize with attributes, data-* and CSS variables:

<div id="lk-demo" style="width:min(100%,64rem);margin-inline:auto">
  <style>
    #lk-demo { display:grid; gap:1rem; align-content:start; font-size:.875rem }
    #lk-demo .lk-grid { display:grid; grid-template-columns:minmax(0,1.35fr) minmax(0,1fr); gap:1rem; align-items:start }
    #lk-demo .lk-card { min-width:0; border:1px solid var(--mv-border); border-radius:var(--mv-radius-xl); background:var(--mv-surface); box-shadow:var(--mv-shadow-sm); overflow:hidden }
    #lk-demo .lk-bar { display:flex; align-items:center; gap:.5rem; height:2.75rem; padding:0 1rem; border-bottom:1px solid var(--mv-border); color:var(--mv-fg-muted); font-size:.75rem; font-weight:500 }
    #lk-demo .lk-bar strong { color:var(--mv-fg); font-size:.8125rem; font-weight:600 }
    #lk-demo .lk-bar .mv-badge { margin-inline-start:auto }
    #lk-demo .lk-mail-head { display:grid; grid-template-columns:auto minmax(0,1fr); gap:.875rem; padding:1rem 1.125rem .875rem; border-bottom:1px solid var(--mv-border) }
    #lk-demo .lk-avatar { display:grid; place-items:center; width:2.25rem; height:2.25rem; border-radius:50%; background:var(--mv-bg-emphasis); color:var(--mv-fg); font-size:.8125rem; font-weight:600 }
    #lk-demo .lk-subject { margin:0 0 .25rem; font-size:1rem; font-weight:650; letter-spacing:-.01em; line-height:1.3 }
    #lk-demo .lk-meta { margin:0; color:var(--mv-fg-muted); font-size:.8125rem; line-height:1.7 }
    #lk-demo .lk-meta b { color:var(--mv-fg-subtle); font-weight:500; display:inline-block; min-width:2.25rem }
    #lk-demo .lk-from { color:var(--mv-fg); font-weight:500 }
    #lk-demo .lk-body { padding:1rem 1.125rem 1.125rem; line-height:1.65; color:var(--mv-fg) }
    #lk-demo .lk-body > p { margin:0 0 .75rem }
    #lk-demo .lk-body > p:last-child { margin:0; color:var(--mv-fg-muted); font-size:.75rem }
    #lk-demo .lk-body a:not(.mv-button) { color:var(--mv-accent); text-decoration-color:color-mix(in oklab,var(--mv-accent) 40%,transparent); text-underline-offset:.2em }
    #lk-demo .lk-form { display:grid; gap:.875rem; padding:1rem 1.125rem 1.125rem }
    #lk-demo .lk-field { display:grid; gap:.375rem; min-width:0 }
    #lk-demo .lk-field > span:first-child { color:var(--mv-fg-muted); font-size:.75rem; font-weight:500 }
    #lk-demo .lk-row { display:flex; align-items:center; gap:.25rem; min-width:0 }
    #lk-demo .lk-row .mv-input { flex:1 1 auto; min-width:0 }
    #lk-demo .lk-mono { font-family:var(--mv-font-mono); font-size:.8125rem }
    #lk-demo .lk-chat { display:grid; gap:.625rem; padding:1rem 1.125rem 1.125rem; max-height:13rem; overflow:auto }
    #lk-demo .lk-msg { display:grid; grid-template-columns:auto minmax(0,1fr); gap:.625rem; align-items:start }
    #lk-demo .lk-msg .lk-avatar { width:1.75rem; height:1.75rem; font-size:.6875rem }
    #lk-demo .lk-msg-who { margin:0; font-size:.75rem; font-weight:600 }
    #lk-demo .lk-msg-who span { color:var(--mv-fg-subtle); font-weight:400; margin-inline-start:.375rem }
    #lk-demo .lk-msg-text { margin:.125rem 0 0; line-height:1.55 }
    #lk-demo .lk-controls { display:flex; align-items:center; gap:.75rem 1.25rem; flex-wrap:wrap; padding:.875rem 1.125rem; border:1px solid var(--mv-border); border-radius:var(--mv-radius-xl); background:var(--mv-bg-subtle) }
    #lk-demo .lk-controls .lk-sep { flex:1 1 0 }
    #lk-demo .lk-ctl { display:flex; align-items:center; gap:.5rem; color:var(--mv-fg-muted); font-size:.75rem; font-weight:500 }
    #lk-demo .lk-log { margin:0; min-height:1.25rem; color:var(--mv-fg-subtle); font:.75rem/1.4 var(--mv-font-mono); flex:1 1 100% }
    #lk-demo .mv-choice { font-size:.8125rem }
    @media (max-width:52rem) { #lk-demo .lk-grid { grid-template-columns:minmax(0,1fr) } }
  </style>

  <mv-lookalike id="lk-main" show-verified trusted="Acme Bank <acme-bank.com>, Lumen Pay <lumenpay.com>, Northwind <northwind.io>, @northwind, Northwind payroll <DE89 3704 0044 0532 0130 00>, Treasury wallet <0x52908400098527886E0F7030069857D2E4169EE7>">
    <div class="lk-grid">
      <!-- An inbox message: sender, links and plain-text addresses are all checked -->
      <article class="lk-card" aria-label="Email message">
        <div class="lk-bar"><strong>Inbox</strong> · Finance shared mailbox <span class="mv-badge" data-variant="outline">Sep 24, 2026</span></div>
        <header class="lk-mail-head">
          <span class="lk-avatar" aria-hidden="true">AB</span>
          <div style="min-width:0">
            <h3 class="lk-subject">Unusual sign-in on your business account</h3>
            <p class="lk-meta"><b>From</b> <span class="lk-from" data-lookalike>Acme Bank Security &lt;[email protected]&gt;</span><br>
              <b>To</b> [email protected]</p>
          </div>
        </header>
        <div class="lk-body">
          <p>Hi Maya, we noticed a sign-in to your Acme Bank business account from São Paulo, Brazil on Sep 23, 2026 at 11:42 PM.</p>
          <p>If this wasn’t you, <a href="https://acmе-bank.com/secure/verify">confirm your identity</a> within 24 hours to avoid a hold on outgoing wires. You can also review recent activity at <a href="https://acme-bank.com.account-review.net/login">acme-bank.com/activity</a>.</p>
          <p>Card payments on your account are processed by lumenpay.co. For anything else, our help center is at <a href="https://acme-bank.com/help">acme-bank.com/help</a>.</p>
          <p>Acme Bank · 400 Harbor Boulevard, Boston, MA 02210</p>
        </div>
      </article>

      <div style="display:grid;gap:1rem;min-width:0">
        <!-- A payment form: fields are checked as you type or paste -->
        <form class="lk-card" aria-label="Send a payment" onsubmit="return false">
          <div class="lk-bar"><strong>Send a payment</strong> · Payouts</div>
          <div class="lk-form">
            <label class="lk-field"><span>Payee email</span>
              <span class="lk-row"><input class="mv-input" type="email" value="[email protected]" autocomplete="off"></span></label>
            <label class="lk-field"><span>Payee IBAN</span>
              <span class="lk-row"><input class="mv-input lk-mono" data-lookalike value="DE89 3704 0044 0532 0180 00" autocomplete="off" spellcheck="false"></span></label>
            <label class="lk-field"><span>Treasury wallet (USDC)</span>
              <span class="lk-row"><input class="mv-input lk-mono" data-lookalike value="0x5290c1b7f04a9d3e6628fb05ac91d7e30b4a9EE7" autocomplete="off" spellcheck="false"></span></label>
            <label class="lk-field"><span>Try it: type or paste any link</span>
              <span class="lk-row"><input class="mv-input" type="url" value="https://www.lumenpay-support.com/invoices" autocomplete="off" spellcheck="false"></span></label>
          </div>
        </form>

        <!-- A team chat: new messages are scanned as they arrive -->
        <section class="lk-card" aria-label="Team chat">
          <div class="lk-bar"><strong>#payouts</strong> · Team chat</div>
          <div class="lk-chat" id="lk-chat">
            <div class="lk-msg"><span class="lk-avatar" aria-hidden="true">JO</span><div><p class="lk-msg-who">Jonas Okafor<span>9:12 AM</span></p><p class="lk-msg-text">September payroll is approved, @northwind can release it.</p></div></div>
          </div>
        </section>
      </div>
    </div>
  </mv-lookalike>

  <div class="lk-controls">
    <label class="mv-choice"><input type="checkbox" role="switch" class="mv-switch" id="lk-intercept" checked> Confirm before opening flagged links</label>
    <span class="lk-ctl"><span id="lk-th-label">Flag from</span>
      <mv-segmented id="lk-threshold" aria-labelledby="lk-th-label" name="threshold" value="lookalike">
        <button value="fine">Similar</button>
        <button value="lookalike">Look-alike</button>
        <button value="impersonation">Impersonation</button>
      </mv-segmented>
    </span>
    <span class="lk-sep"></span>
    <button type="button" class="mv-button" data-variant="outline" data-size="sm" id="lk-incoming">Receive a chat message</button>
    <p class="lk-log" id="lk-log" aria-live="polite">Click a flag, or a flagged link, to see what doesn’t match.</p>
  </div>

  <script type="module">
    const lk = document.getElementById("lk-main");
    const log = document.getElementById("lk-log");
    const say = (text) => { log.textContent = text; };

    // Demo only: never actually open the fake addresses.
    lk.addEventListener("mv-lookalike-proceed", (e) => {
      e.preventDefault();
      lk.close();
      say(`mv-lookalike-proceed · would continue to ${e.detail.href ?? e.detail.value} (cancelled in this demo)`);
    });
    lk.addEventListener("mv-lookalike-report", (e) => say(`mv-lookalike-report · ${e.detail.verdict}: ${e.detail.value}`));
    lk.addEventListener("mv-lookalike-found", (e) => say(`mv-lookalike-found · ${e.detail.result.title}: ${e.detail.value}`));
    lk.addEventListener("click", (e) => {
      const real = e.target.closest?.(".mv-lookalike-real");
      if (real) { e.preventDefault(); say(`Would open the real site: ${real.href}`); }
    });

    document.getElementById("lk-intercept").addEventListener("change", (e) => { lk.intercept = e.target.checked ? "true" : "false"; });
    document.getElementById("lk-threshold").addEventListener("mv-change", (e) => { lk.threshold = e.detail.value; });

    const incoming = [
      ["NR", "Northwind Treasury", "@n0rthwind here: urgent, update the payout wallet before 5 PM using the form at lumenpay.help/payouts"],
      ["PL", "Priya Lal", "Invoices for Q3 are on northwind.io/finance, and the vendor list is at lumenpaay.com/vendors"],
      ["AK", "Ana Kovač", "Heads-up, I got a text from acme-bnak.com asking me to confirm a transfer. Ignored it."],
    ];
    let next = 0;
    document.getElementById("lk-incoming").addEventListener("click", () => {
      const [initials, who, text] = incoming[next++ % incoming.length];
      const chat = document.getElementById("lk-chat");
      const time = new Date().toLocaleTimeString("en-US", { hour: "numeric", minute: "2-digit" });
      const msg = document.createElement("div");
      msg.className = "lk-msg";
      const avatar = Object.assign(document.createElement("span"), { className: "lk-avatar", textContent: initials });
      avatar.setAttribute("aria-hidden", "true");
      const body = document.createElement("div");
      const name = Object.assign(document.createElement("p"), { className: "lk-msg-who", textContent: who });
      name.append(Object.assign(document.createElement("span"), { textContent: time }));
      body.append(name, Object.assign(document.createElement("p"), { className: "lk-msg-text", textContent: text }));
      msg.append(avatar, body);
      chat.append(msg);
      chat.scrollTop = chat.scrollHeight;
    });
  </script>
</div>

Cultural reference

Little Red Riding Hood, Charles Perrault (1697, fable). The wolf lies in the grandmother’s bed looking almost right, and the girl notices, one by one, the details that don’t fit before it is too late. The UI compares every link, sender or account with the one the user trusts and names each detail that doesn’t fit, one by one, before the click.

API

Attributes

Name	Type	Default	Description
`trusted`	comma-separated list		Trusted identities. Each entry is a domain (acme-bank.com, also trusts its subdomains and email addresses), an email domain (@stripe.com), an address ([email protected], trusted by its domain), a handle or name (@northwind, left-pad) or an account (IBAN, 0x… or bc1… wallet). Prefix a label with the email syntax to name it in messages and buttons: “Acme Bank <acme-bank.com>”. The identities property replaces this list when set.
`threshold`	fine \| lookalike \| impersonation	`lookalike`	Lowest verdict that gets a flag (and link interception). fine also flags faint resemblances (“Probably fine”), impersonation only flags deliberate disguises.
`intercept`	"true" \| "false"	`true`	Clicks (and middle clicks) on flagged links open the explanation as a confirmation instead of navigating. Continue anyway replays the click natively, so target, rel and client-side routers behave as usual.
`scan`	space-separated: links text fields	`links text fields`	What is checked: links (a[href] with http(s):, mailto: or //), text (domains, emails, @handles, IBANs and 0x wallets written in plain text, wrapped in a span.mv-lookalike-mark only when flagged) and fields (input[type=email], input[type=url] and any input or textarea with data-lookalike, on input, paste, change and blur). Elements with data-lookalike are always checked.
`show-verified`	boolean		Exact matches of a trusted identity get a small shield-check mark with a “Verified: {label}” text alternative.
`validate`	boolean		Flagged fields get a custom validity message (form submission is blocked) until the user picks Use the real value or Continue anyway.
`data-lookalike (on content)`	empty \| value		Checks this element: its text (“Acme Bank Security <[email protected]>” is parsed as display name + address), the attribute value if given, a link’s href, or a field’s value. data-lookalike-name="…" adds a display name to check against the address. data-lookalike-ignore skips a subtree.
`data-lookalike-verdict (set on content)`	impersonation \| lookalike \| fine \| trusted		Set by the component on every flagged link, mark, element or field (styleable); data-lookalike-ack once the user chose Continue anyway.
`data-found`	boolean		Set on the element while at least one suspicious item is flagged.

Properties

Name	Type	Description
`identities`	Array`<string \| { value, label?, href? }>`	Trusted identities as data (replaces the trusted attribute). href overrides the “Go to the real X” destination (defaults to https://`<domain>`). Read it to get the parsed list with kinds.
`results`	Array<{ element, value, verdict, result, acknowledged, reported }>	Every flagged or verified item currently in scope (read-only).
`strings`	Partial<Record<string, string>>	Overrides for every visible text, announcement and difference message ({label}, {value}, {c}, {t}, {count}… placeholders; “{c}” renders as inline code). English defaults.
`threshold / intercept / scan / showVerified / validate`	reflected	Mirror the attributes.

Methods

Name	Description
`MvLookalike.compare(candidate, trusted, { strings? })`	Static and pure (also exported as compare): compares one value with one identity. Returns { verdict: "trusted" \| "impersonation" \| "lookalike" \| "fine" \| "unrelated", score (0-1 resemblance), kind (domain \| email \| name \| account), value, display, trusted, label, href, title, diffs: [{ n, type, key, vars, message }], rows: { shown, candidate, trusted } (segments { text, n, type, gap } for side-by-side rendering) }. No DOM, safe in Node, Deno, workers.
`MvLookalike.check(value, trusted[], options?)`	Static and pure (also exported as check): compares a value with every identity and returns the most telling result (an exact match wins). checkLink(href, text, trusted) also flags link texts that claim another address.
`check(value)`	Same as the static check, against this element’s identities.
`rescan()`	Re-checks the whole scope now. Content added later (a new chat message, a re-render) is picked up automatically by a MutationObserver.
`open(element) / close()`	Opens the explanation for a flagged link, field or marked element, or closes it.

Events

Name	Description
`mv-lookalike-found`	A suspicious item was flagged (initial scan, new content or a field value). detail: { element, kind: "link" \| "text" \| "marked" \| "field", value, verdict, result }.
`mv-lookalike-proceed`	Cancelable. The user chose Continue anyway. detail: { element, kind, value, href (links), verdict, result }. preventDefault() keeps the warning (and, for an intercepted link, does not open it).
`mv-lookalike-report`	The user chose Report (once per item; the flag then reads “· Reported”). detail: { element, kind, value, verdict, result }. Send it to your abuse or security endpoint.

CSS classes

Name	Description
`mv-lookalike-flag`	Inline flag `<button>` placed right after the item (data-verdict, aria-expanded, data-ack, data-reported): an icon, .mv-lookalike-flag-text and a visually hidden verdict.
`mv-lookalike-mark`	Span wrapped around a suspicious address found in plain text (never around unflagged text; unwrapped when no longer flagged).
`mv-lookalike-verified`	Shield-check mark after exact matches with show-verified.
`mv-lookalike-panel`	Explanation panel (non-modal dialog in the Popover API top layer, data-verdict, data-intercept): -head, -icon, -kicker, -title, -text, -close, -compare (rows of -label + -value with .mv-lookalike-diff / .mv-lookalike-gap and numbered .mv-lookalike-num), -diffs (the numbered explanations, .mv-lookalike-code), -status, -actions (-report, -proceed, -real, -use).

CSS variables

Name	Default	Description
`--mv-lookalike-danger`	`var(--mv-danger)`	Tone of impersonations: underline, flag, highlights.
`--mv-lookalike-warn`	`var(--mv-warning)`	Tone of look-alikes.
`--mv-lookalike-ok`	`var(--mv-success)`	Tone of verified marks and of the trusted row’s highlights.

Accessibility

Every flag is a real <button> with visible words (“Impersonation”, “Look-alike”, “Similar”) plus a visually hidden verdict (“: Impersonates Acme Bank. Show the differences.”), aria-haspopup="dialog", aria-expanded and aria-controls; the wavy underline is never the only signal. The panel is a labelled, described non-modal dialog inserted right after the flag (outside any label, link or button), so Tab moves on naturally; it receives focus when opened from a flag, and on an intercepted link focus goes to the safe action (Go to the real X) rather than Continue anyway. Escape or Close folds it and returns focus to the flag or link; an outside click or moving focus elsewhere closes it too. Differences are spelled out in text, never shown by color alone: the side-by-side rows keep the real characters, each difference is numbered in both rows and in an ordered list of sentences that name the character, its script and code point (“The “а” here is Cyrillic (U+0430), not the Latin letter “a”.”), what was added, missing, swapped or replaced; the numbers are aria-hidden duplicates of the list order. Flagged fields get an extra aria-describedby text with the verdict, an optional custom validity message (validate), and a polite announcement when a typed or pasted value becomes suspicious; new suspicious content (a chat message) is announced politely once per batch; the initial scan is silent. Verified marks carry a text alternative. The one-by-one reveal of the differences and highlights is disabled under reduced motion (OS or data-motion="reduce"), and forced-colors mode keeps highlights as system Mark colors with outlines.