CrowdyPy

The official Python SDK for Crowded Kingdoms: typed clients for the platform's one GraphQL API (identity, studio administration, world data, ck-exec) and a native UDP replication core.

CrowdyPy follows the CrowdyJS API surface (the same domains, the same two-token model, the same error codes) the way CrowdyCPP does, with Python names (mintAppToken is mint_app_token). Its realtime path is CrowdyCPP's native replication client, bound with nanobind and shipped inside the wheel. Python never touches a datagram.

v0.4.0: headless Crowdy Studio, and full parity with CrowdyJS.

• crowdypy.studio.CrowdyStudioController is the Studio editor without a browser: open projects, edit with autosave and revision conflicts, bind GitHub, apply agent patches with checkpoints, and build, deploy and run mods. StudioLayoutController and parse_rustc_diagnostics match CrowdyJS byte for byte.
• The roots CrowdyCPP sends and CrowdyJS does not are wrapped too: email confirmation, usage projections, compute budgets, listing versions, the narrow Studio mutations, and client.crowdy_studio_agent.
• crowdypy.player_host is the typed observation contract a game implements so tooling can read the player it controls, validated exactly as CrowdyJS validates it.
• The parity gate is strict: docs/parity-matrix.md has no gaps.
• 0.3.0 brought the World Stores, the Game Kit, ck-exec and subscriptions; 0.2.0 native UDP replication (client.udp); 0.1.0 the GraphQL client.

See MIGRATION.md.

Install

pip install crowdypy

Wheels: CPython 3.12+ (one abi3 wheel per platform) and free-threaded CPython 3.14, on Linux x86_64 / aarch64, macOS arm64 / x86_64 and Windows x64. OpenSSL is linked statically; nothing else native is needed. docs/compatibility.md has the details, including the tier versions below.

Each tier of the platform has its own release line, and a build defaults to its own tier's API origin (crowdypy.CROWDY_DEFAULT_TIER says which):

pip skips pre-releases unless a requirement names one, so a prod range never picks up a dev or test build. The same wheels are attached to each GitHub release.

Quick start

import asyncio

import crowdypy

API = "https://ck.dev.crowdedkingdoms.com"


async def main() -> None:
    # The identity client: sign-in, account and studio calls, minting.
    async with crowdypy.AsyncCrowdyClient(http_url=API) as identity:
        await identity.auth.login("player@example.com", "correct-horse-battery")
        minted = await identity.portal.mint_app_token("42")

    # The game client: one per app, at the app's own datacenter.
    async with crowdypy.AsyncCrowdyClient(
        http_url=minted.game_api_url or API, discovery_url=minted.discovery_url
    ) as game:
        game.set_app_token(minted)
        print(await game.server_status.server_with_least_clients())


asyncio.run(main())

Without an event loop, crowdypy.sync.CrowdyClient has the same methods, without await:

from crowdypy.sync import CrowdyClient

with CrowdyClient(http_url=API) as identity:
    identity.auth.login("player@example.com", "correct-horse-battery")
    print(identity.users.me())

Two tokens, two clients

There is one API origin but two tokens, as in every Crowded Kingdoms SDK:

1. Sign-in (auth.login, a magic link, or social/OIDC) yields an identity session token: account, studio administration and minting. It is not accepted for gameplay.
2. Gameplay needs a short-lived app-scoped token per app (portal.mint_app_token(app_id)), which is also the HMAC key for native UDP. Refresh it with client.refresh_gameplay_token() (concurrent callers share one refresh).
3. Build one identity client and one client per game. The game client points at the app's datacenter (game_api_url) with discovery_url set, so it can find the app again if that instance stops answering.

Persist them the same way: FileTokenStore.session_path(directory, api_origin) names the session file (one per origin, shared by every game) and FileTokenStore.app_path(directory, app_id) the gameplay one (one per app):

from crowdypy import FileTokenStore

identity = crowdypy.AsyncCrowdyClient(
    http_url=API, token_store=FileTokenStore(FileTokenStore.session_path(state_dir, API))
)

CrowdyPy sends no Origin header, so direct sign-in is served to it; hosted browser sign-in (portal.signIn in CrowdyJS) is a browser flow and is not part of this SDK.

Errors

Every error is a crowdypy.CrowdyError. A GraphQL refusal is a CrowdyGraphQLError with the server's stable code (error.code == "FORBIDDEN") and extensions; HTTP, network and timeout failures have their own classes. CrowdyAppUnavailableError (the app's datacenter is not serving) and CrowdyUserCodeFaultError (a player module faulted; player_fault_of(error) reads the fault) mirror CrowdyJS. A WRONG_DATACENTER refusal moves the client to the app's datacenter and retries once, by itself.

Replication

minted = await identity.portal.mint_app_token("42")
async with crowdypy.AsyncCrowdyClient(
    http_url=minted.game_api_url or API, discovery_url=minted.discovery_url
) as game:
    await game.udp.connect(minted)  # assign a server, open the socket
    game.udp.subscribe({"actor_update": lambda n: print(n.uuid, n.chunk, n.payload)})
    await game.udp.send_actor_update((0, 0, 0), my_uuid, pose_bytes)
    echo = await game.udp.send_actor_update_and_wait((0, 0, 0), my_uuid, pose_bytes)

For a game loop, use the connection underneath: send a frame's entities in one call, and read whole batches.

conn = game.udp.connection
conn.send_actor_updates(chunks, uuids, poses, stride=88)  # numpy (n, 3) int64, n x 32 octets
async for batch in conn.batches():
    actors = batch.types == crowdypy.wire.MessageType.ACTOR_UPDATE_NOTIFICATION
    positions = batch.chunks[actors]  # a view, not a copy

crowdypy.replication.ReplicationConnection is the same for code without an event loop: wait() and then poll() from your own loop.

World Stores

from crowdypy.codecs import f32, struct_codec, u16
from crowdypy.stores import create_world_session

pose = struct_codec({"x": f32(), "y": f32(), "z": f32(), "yaw": u16()})
session = create_world_session(game, app_id, actor_codec=pose, host=True, save=True)
session.self.join((0, 0, 0), {"x": 0.0, "y": 64.0, "z": 0.0, "yaw": 0})
session.actors.on_join(lambda actor: print("joined", actor.uuid, actor.value))
asyncio.create_task(session.run())  # tick 60 times a second

snapshot = session.actors.snapshot()  # once a frame: every actor at once
states = pose.decode_many(snapshot.state_offsets, snapshot.state_data)  # numpy, no loop

Crowdy Studio

from crowdypy.studio import CrowdyStudioController

studio = CrowdyStudioController.for_client(game, app_id=app_id, grid_id=grid_id)
await studio.initialize()  # opens the first project
studio.update_file("SERVER", "src/lib.rs", source)  # autosaves
result = await studio.test_draft()  # build, deploy and switch on the mod
print(result.status, studio.get_state().build_output)

A CLIENT target runs in a host you pass as broker_factory; the browser Studio runs it in a Web Worker.

Performance

Python does no work per datagram. Receive, HMAC verification and decoding happen on CrowdyCPP's network thread, which never takes the GIL; Python sees one batch object per poll. Sends release the GIL, and a batch releases it once for the whole batch. An asyncio loop is woken through a socket, not by polling. Measured against CrowdyCPP on the same machine (benchmarks/README.md): a 200-entity batch costs 1.06x CrowdyCPP's own send path per entity, Python takes in two million verified notifications a second, a notification reaches an asyncio handler 47 µs after it hits the wire (p50), and a 60 Hz loop stays within 0.2 ms of its schedule while receiving 60,000 a second.

Development

uv sync                       # builds the extension (CMake, a C++20 compiler) and installs dev tools
uv run pytest tests/unit
uv run ruff check . && uv run ruff format --check . && uv run mypy

The live suites in tests/e2e/ run against a deployment when the CROWDY_E2E_* variables are set; docs/e2e-coverage.md lists them, how to configure them and the last live runs.

The gates CI runs, all from a clean checkout:

AGENTS.md covers maintenance: re-pinning CrowdyJS and CrowdyCPP, the tier branches and the release path.

License

MIT. Wheels also contain CrowdyCPP (MIT), yyjson (MIT) and OpenSSL (Apache-2.0).