jero 0.0.4

An opinionated, msgspec-first ASGI micro-framework

jero

An opinionated, msgspec-first ASGI micro-framework for Python 3.14.

• GitHub: https://github.com/RogerThomas/jero/
• Documentation: https://RogerThomas.github.io/jero/

What is jero?

jero is built on three non-negotiable pillars:

1. Speed. All introspection happens once, at wiring time. The per-request path is just dict lookup → msgspec decode → call → encode — nothing else.
2. Opinionated, scaffolded DX. There is one blessed way to do each thing. Contracts are checked at startup and fail loud with a precise WiringError, never silently at runtime.
3. Strict, expressive typing. Everything is fully, statically typed under pyright-strict. Types are the contract — the binding, the wiring errors, and (on the roadmap) the source of the OpenAPI spec.

It deliberately has no DI container: you hand-wire dependencies in _wire, and the framework owns only what the language doesn't give you for free — lifecycle.

Example

from msgspec import Struct

from jero import BaseApp, Endpoint, Resource, TestClient


class Widget(Struct):
    id: str
    name: str


class WidgetResource(Resource):
    async def read_one(self, path: "WidgetPath") -> Widget:
        return Widget(id=path.widget_id, name="widget-name")


class WidgetPath(Struct):
    widget_id: str


class HealthEndpoint(Endpoint):
    async def get(self) -> Widget:
        return Widget(id="health", name="ok")


class App(BaseApp):
    async def _wire(self) -> None:
        self._include_resource(WidgetResource(), path="/widgets")
        self._include_endpoint(HealthEndpoint(), path="/healthz")


app = App()

# Test it in-process — no socket, no server:
with TestClient(app) as client:
    resp = client.get("/widgets/abc")
    assert resp.status_code == 200
    assert resp.json() == {"id": "abc", "name": "widget-name"}

Run it under any ASGI server, e.g. granian:

granian --interface asgi myapp:app

Development

task install   # create the venv and install pre-commit hooks
task check     # lock check + ruff, pyright, deptry, pylint (via prek)
task test      # run the test suite with coverage

See AGENTS.md for the design philosophy and the contract, and style-guide.md for project conventions.

Releasing a new version

Publishing uses PyPI Trusted Publishing (OIDC) — no token required.

1. Bump version in pyproject.toml and commit it to main.
2. Create a GitHub release tagged with the same version — a bare PEP 440 string, e.g. 0.1.0 (no v).

The release workflow verifies the tag matches pyproject.toml, builds, publishes to PyPI, and deploys the docs. A version mismatch fails the release.

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Repository initiated with osprey-oss/cookiecutter-uv.