@formstr/signer

A vanilla TypeScript Nostr signer with an optional unstyled login UI. Supports NIP-07 (browser extension), NIP-46 (bunker URI + nostrconnect QR), NIP-49 (ncryptsec at rest), and NIP-55 (Android external signer apps).

Install

pnpm add @formstr/signer

Quick start

import { createSigner } from '@formstr/signer';

// `appName` is required if you plan to use nostrconnect (NIP-46 QR flow) —
// see "NIP-46 app identity" below. Other login methods don't depend on it.
const signer = createSigner({ appName: 'my-app' });

// Create a new account (NIP-49 ncryptsec encrypted at rest)
const { npub, ncryptsec } = await signer.createAccount('my-passphrase');

// Subsequent sessions: log in with the encrypted nsec
await signer.loginWithNcryptsec(ncryptsec, 'my-passphrase');

// Or any of the other methods
await signer.loginWithExtension();
await signer.loginWithBunkerUri('bunker://...');
await signer.loginWithNostrConnect({ relays: ['wss://relay.example'], onUri: (uri) => /* show QR */ });
await signer.loginWithAndroidSigner({ packageName: 'com.greenart7c3.nostrsigner' });

// Sign events — the active signer never exposes the privkey
const active = signer.getActiveSigner()!;
const signed = await active.signEvent({ kind: 1, content: 'gm', tags: [], created_at: 0 });

Account model

A StoredAccount is the persisted record for one identity. Accounts survive page reloads via the configured StorageAdapter. Listing, switching, and removing are independent of unlock state.

signer.listAccounts();          // every persisted account
signer.getActiveAccount();      // currently selected — present even when locked
signer.getActiveSigner();       // unlocked signer — null until re-auth
await signer.switchAccount(pubkey);
await signer.logout(pubkey);    // pubkey defaults to active

const unsub = signer.onChange((ev) => {
  // ev.type is 'login' | 'switch' | 'logout'
});

Hydration & locked state

The single most important thing to understand about this package: after a fresh page load, every account starts locked. That means:

• listAccounts() returns the saved accounts.
• getActiveAccount() returns the account that was active before reload.
• getActiveSigner() returns null, regardless of method.

To unlock, call the matching loginWith* again:

The pattern in the UI is: always render off getActiveAccount(), gate signing on getActiveSigner(). Show "logged in as @alice" plus an "Unlock" button when the signer is null.

The ActiveSigner contract

Every unlock path produces an ActiveSigner. The interface is intentionally small:

interface ActiveSigner {
  getPublicKey(): Promise<string>;
  signEvent(event: EventTemplate): Promise<NostrEvent>;
  nip04Encrypt(peerPubkey: string, plaintext: string): Promise<string>;
  nip04Decrypt(peerPubkey: string, ciphertext: string): Promise<string>;
  nip44Encrypt(peerPubkey: string, plaintext: string): Promise<string>;
  nip44Decrypt(peerPubkey: string, ciphertext: string): Promise<string>;
}

• signEvent accepts an EventTemplate (no pubkey/id/sig); the implementation fills those in and returns a fully-signed event.
• peerPubkey is the counterparty's 32-byte x-only hex pubkey.
• There is no getPrivateKey(). That omission is the package's central security invariant — the raw key is unreachable through this surface, even for the local-key signer.

Building a custom signer (hardware wallet, MPC, browser-stored hot wallet) is a matter of conforming to this interface. The package does not currently expose a way to register a custom signer type into a StoredAccount; you'd hold the instance yourself and pass it into your event-signing path directly.

NIP-55 (Android) custom plugins

The default expectation is that you pass nostr-signer-capacitor-plugin as androidSignerPlugin. To plug in a different implementation, conform to AndroidSignerPlugin:

import type { AndroidSignerPlugin } from '@formstr/signer';

const myPlugin: AndroidSignerPlugin = {
  setPackageName(packageName) { /* ... */ },
  getInstalledSignerApps() { /* ... */ },
  getPublicKey(packageName, permissions) { /* ... */ },
  signEvent(packageName, eventJson, id, npub) { /* ... */ },
  nip04Encrypt(packageName, plainText, id, pubKey, npub) { /* ... */ },
  // nip04Decrypt, nip44Encrypt, nip44Decrypt likewise
};

The interface signatures intentionally mirror nostr-signer-capacitor-plugin's exported NostrSignerPlugin so the real wrapper is directly assignable. If you write a custom plugin, the package's test suite includes a compile-time conformance guard (tests/helpers/mockAndroidPlugin.ts) you can model your own check on — wire it up in your CI and you'll catch any drift the moment the upstream wrapper changes shape.

NIP-46 app identity (required for nostrconnect)

The nostrconnect URI you generate must include a name (and ideally url/image) so remote signer apps can show the user which app is asking to pair. Without it:

• Amber receives the request but never surfaces an approve/deny prompt — the consent UI requires a recognizable client identity. The pairing silently stalls.
• Other signers will at minimum display a shortened pubkey hex instead of your app name.

The package enforces this at runtime — loginWithNostrConnect() throws if no name can be resolved:

@formstr/signer: loginWithNostrConnect requires an app name. Set `appName` in createSigner() or pass `metadata.name` to loginWithNostrConnect().

Two ways to supply it. Set once at construction (recommended for most apps):

const signer = createSigner({
  appName: 'my-app',
  appUrl: 'https://my-app.example',           // optional
  appImage: 'https://my-app.example/icon.png', // optional
});
await signer.loginWithNostrConnect({ relays: ['wss://...'], onUri });

Or override per call:

await signer.loginWithNostrConnect({
  relays: ['wss://...'],
  onUri,
  metadata: { name: 'temporary-name', url: '...', image: '...' },
});

Per-call metadata.* fields override config defaults field-by-field — set metadata.name without metadata.url, and the config's appUrl still applies.

The bunker:// flow (loginWithBunkerUri) is unaffected — NIP-46 has no spec slot for client metadata in that flow, and Amber recognizes apps via the secret embedded in the bunker URI it generated. App name shown there comes from what the user named the connection inside Amber.

UI helpers

The UI module returns HTML strings. The calling code injects the markup wherever it wants and then calls attach*Listeners() to wire events.

import { renderLoginHtml, attachLoginListeners } from '@formstr/signer/ui';
import '@formstr/signer/styles.css'; // optional

const container = document.getElementById('signer-root')!;
container.innerHTML = renderLoginHtml();
const detach = attachLoginListeners(container, signer, {
  onLogin: ({ npub }) => console.log('logged in', npub),
  onError: (err) => console.error(err),
});

// later: detach();

The login modal renders one tab per method (Create, Existing key, Extension, Bunker URI, Remote QR, Android). The Android tab is always rendered but its list of installed signers is fetched lazily on activation via signer.listAndroidSignerApps() — it errors clearly if no Android plugin is configured (e.g. when running on web).

Errors

All loginWith* methods reject with bare Error instances. Categories you can expect:

• Validation — empty passphrase, empty relays, malformed bunker URI.
• Wrong credential — loginWithNcryptsec with a bad passphrase throws synchronously after decrypt.
• External denial — extension/bunker/Android signer rejects the request.
• Transport — NIP-46 relay unreachable, pairing timeout, abort.
• Configuration —
  • loginWithNostrConnect throws if neither appName (in createSigner) nor metadata.name (per call) is set. See "NIP-46 app identity" above.
  • loginWithAndroidSigner / listAndroidSignerApps throws if no plugin is configured.

Error messages are prefixed with @formstr/signer: for messages the package generates itself. Errors from nostr-tools or the Capacitor plugin propagate unchanged. There is currently no typed code field — discriminate by string match or by which method threw.

Security model

• Identity nsec at rest: always encrypted with the user's passphrase (NIP-49). Account creation always requires a passphrase — there is no "guest" raw-nsec path.
• Decrypted privkey: held in memory only, for the lifetime of the page. Never written to localStorage or sessionStorage. Lost on page reload — the user re-enters the passphrase.
• Active signer interface: exposes signEvent, nip04*, nip44*, getPublicKey only. There is no method that returns the raw private key.
• NIP-46 relays: for bunker URIs, relays come from the URI. For the nostrconnect QR flow, the UI prompts the user for relays. There is no hardcoded fallback relay list.
• NIP-46 client secret: the per-account ephemeral keypair used to talk to the remote signer is stored in plaintext in the configured storage adapter. This is a deliberate tradeoff — see the threat-model note below.

Threat-model note on the NIP-46 client secret

The client secret is not the user's identity key — it is a disposable session key the remote signer recognizes as the client. An attacker with same-origin storage access could impersonate the client to the remote signer; whether that results in unauthorized signatures depends on whether the user has granted blanket permissions on the bunker side (out of our control). Encrypting this secret with a derivable key would not defend against same-origin XSS (the realistic attacker), so we keep it plaintext rather than adding security theater.

BEM class catalog

The UI ships with these class names. Override in your own CSS.

Layout

Tabs

Panels

Forms / inputs

Android signer list

QR

Buttons / status