at_client: the platform-neutral Dart SDK, for command-line apps, headless services, and Internet-of-Things devices. Owns the whole atSign lifecycle — Atsign('@alice').open, .activate and .enroll hand back an AtClient — as well as collections, sync, notifications and encryption.
at_client_flutter: the Flutter layer on top of at_client, for mobile and desktop apps. Adds onboarding / authentication dialogs and device-keychain storage. Flutter web is not a supported target.

Libraries

Build Status

Dart libraries for building Atsign Platform applications. All are published on pub.dev.

at_auth: the protocol layer under at_client's lifecycle verbs: CRAM activation, the APKAM enrollment handshakes, the .atKeys key stores and the registrar client. Applications reach it through at_client.
at_chops: cryptographic and hashing operations (encryption, decryption, signing, hashing) used by the rest of the SDK, including the post-quantum primitives.
at_cli_commons: helpers for Dart CLI / server programs that use at_client. Wraps the boilerplate of parsing flags, loading keys, and producing an authenticated AtClient.
at_commons: foundational types used across every package: keys, metadata, atSign validation, root-domain parsing, verb builders for the Atsign Protocol wire format, and the exception hierarchy.
at_contact: contacts library that persists across different Atsign Platform applications.
at_lookup: low-level direct implementation of the Atsign Protocol verbs. Used by at_client and at_client_flutter.
at_onboarding_cli: the at_register and at_activate command-line tools for registering, activating and enrolling atSigns, and a small library for programs that drive the same flows headlessly.
at_policy: scaffolding for building policy-management services that talk to enforcement endpoints via the Atsign Protocol.
at_server_status: logs the status of the root server and the atServer for an atSign of your choice.
at_utils: utility library: atSign, metadata, configuration, logger.
base2e15: fork of the upstream base2e15 package, kept here for null-safety support.
dart_utf7: fork of the upstream utf7 package, kept here for null-safety support.

Flutter packages

Build Status

Status: Most of the at_*_flutter packages listed below are in the process of being deprecated. Over the next few months they'll be replaced by example application code rather than reusable widget packages. The recommended path for new Flutter work is to read the example app at packages/at_client_flutter/examples/todos and adapt it directly. The packages will continue to publish until that migration completes.

at_backupkey_flutter: deprecated; export the keys with FileAtKeysIo as the at_client_flutter README shows.
at_chat_flutter: chat feature using atSigns and the Atsign Protocol.
at_common_flutter: common widgets used by other Atsign Flutter packages. Already deprecated in favour of at_client_flutter.
at_contacts_flutter: contact-management widgets for atSign-based apps.
at_contacts_group_flutter: group functionality on top of at_contacts_flutter.
at_events_flutter: event management.
at_follows_flutter: a basic social "follows" feature for atSigns.
at_invitation_flutter: deprecated; invite contacts via SMS or email using the at_client_flutter snippet.
at_location_flutter: share location between two atSigns and view on OpenStreetMap.
at_login_flutter: zero-trust logins using the Atsign Protocol.
at_notify_flutter: notification surface.
at_sync_ui_flutter: UI indicator for the SDK's sync process.
at_theme_flutter: theme switching.

Post-quantum cryptography

The SDK can protect everything an adversary could record today — data shared between atSigns, an atSign's own data, and the secrets an enrollment approval hands a new device — with post-quantum key establishment, and can authenticate with a post-quantum signature. It is opt-in per client, through one setting:

final preference = AtClientPreference(posture: PqPosture.pqReady)
  ..namespace = 'todos';

Posture	Authentication	Data written	Reads post-quantum data
`PqPosture.legacy` (default)	RSA-2048	legacy encryption	no
`PqPosture.pqReady`	ML-DSA-65; publishes a key package and this atSign's namespace keys	legacy encryption, so pre-quantum peers read it	yes
`PqPosture.pqActive`	ML-DSA-65, and an ML-DSA-65 data signing key	post-quantum by default; legacy writes refused	yes

Under the hood, each namespace an atSign owns gets a key-establishment keypair — the X-Wing hybrid (ML-KEM-768 + X25519) by default, pure ML-KEM-1024 on request — published as a signed advertisement; a writer establishes a content key to the recipient's namespace key and encrypts the record with AES-256-GCM, and a sender follows whatever the recipient advertised. An enrollment submitted under a post-quantum posture advertises a key package, and the approving client seals the atSign's secrets to it rather than wrapping them with RSA. A client whose posture asks for a stronger authentication key than its enrollment holds re-enrolls itself at its first start, filing the new enrollment in the same keys store beside the legacy fields. ML-DSA authentication needs an atServer that verifies it; a legacy client makes no such demand.

The default posture moves one stage per major of at_client — 3.x legacy, 4.x pqReady, 5.x pqActive — because a record may only be written in a scheme every reader of it supports, so the stage that reads post-quantum data rolls out before the stage that writes it by default. An app on 3.x names pqReady or pqActive to move first.

The developer's view, the goals and the ladder are in the at_client README; the design is under docs/projects/pq/.

Upgrading

Applications talk to at_client (3.x, a minor release), so most need no code change: the new lifecycle verbs sit beside AtClientManager, whose setCurrentAtSign is deprecated rather than removed. The packages that take a major are the ones that used to hand at_auth's types to an app:

at_client_flutter 1.x → 2.0: AuthService and FlutterEnrollmentService are gone; the dialogs take the atSign, the keys store and the preference, and hand back the AtClient. Nothing from at_auth is re-exported. The table is in the at_client_flutter README.
at_onboarding_cli 1.x → 2.0: at_activate names its command (at_activate onboard -a @alice), --posture replaces --signingAlgoType, and AtOnboardingService keeps authenticate() and atClient while onboard, enroll and close become Atsign.activate, Atsign.enroll and atClient.stop(). The table is in the at_onboarding_cli README.
at_auth 3.x → 4.0: AtAuth and its request and response objects are gone; activation is activateAtSign(...), logging in and every enrollment decision are at_client's. The table is in the at_auth README.

If you happen to import at_onboarding_cli or at_auth directly — which almost no application does — the short version is: replace the call that built your client with Atsign('@alice').open(keys: ..., preference: ...), .activate(...) or .enroll(...), drop the import, and read everything else off the AtClient you get back.

Installation

Each package's own README and pub.dev page have the installation details. Click any of the links above.

AI Agent Skill

The at_client_skills package gives AI agents accurate, up-to-date knowledge of at_client and at_client_flutter — covering AtCollection<T>, auth flows, querying, sub-collections, testing patterns, and common pitfalls.

# Add to your project
dart pub add --dev at_client_skills skills

# Install the skill into your IDE
dart run skills get

Works with Claude Code, Cursor, GitHub Copilot, Cline, and any agent supporting the agentskills.io specification.

Maintainers

Atsign Foundation core devs