Agnara

Capability-native Python for the agentic era.

Agnara is a Python 3.14-native capability framework for services meant to be consumed by humans, applications and AI agents without making HTTP the centre of the architecture. A capability is declared once, with its effects, risk and confirmation requirements, and later exposed through whichever protocol the caller needs.

This distribution is agnara, the capability-first, transport-neutral execution kernel: the capability model, registry, execution context, dependency graph, policies, execution planning and canonical errors. It depends on nothing but the standard library.

Stable 1.x kernel

This 1.0.3 distribution follows Agnara's stable 1.x public API contract. The source tree prepares the package; consult PyPI for publication status. The kernel remains standard-library-only. HTTP, MCP, CLI and telemetry live in separate, synchronized distributions; the A2A and events packages currently reserve namespaces without runtime APIs.

Install

pip install agnara

For reproducible installations after publication, pin the synchronized version:

pip install "agnara==1.0.3"

Requires CPython 3.14 or newer.

Quick start

import asyncio

from agnara import Agnara, Principal, Risk, StandardEffect
from agnara.di import DIContainer, DIRegistry
from agnara.execution import (
    ExecutionContext,
    ExecutionPlan,
    Invocation,
    invoke_result,
)

app = Agnara("billing")


@app.capability(
    description="Refund a captured payment.",
    scopes=("billing:write",),
    effects=(StandardEffect.FINANCIAL_WRITE,),
    risk=Risk.HIGH,
)
def refund(payment_id: str, amount_cents: int) -> str:
    return f"refunded {amount_cents} cents for {payment_id}"


async def main() -> None:
    capabilities = app.compile()
    dependencies = DIRegistry()
    plan = ExecutionPlan.compile(capabilities["billing.refund"], dependencies)

    outcome = await invoke_result(
        plan,
        ExecutionContext(
            Invocation(
                capability_id=plan.definition.id,
                payload={"payment_id": "pay_123", "amount_cents": 2500},
                metadata={},
            ),
            DIContainer(dependencies),
            principal=Principal("quickstart", scopes={"billing:write"}),
        ),
    )
    print(outcome)


asyncio.run(main())

The declared function is returned unchanged, so it stays directly callable and directly testable. Registration is a side effect on the application, not a transformation of the function.

Kernel capabilities

• capability declaration and a deterministic, freezable registry;
• stable capability identity, plus effect, risk, idempotency and confirmation metadata;
• a schema port with a standard-library adapter and compiled per-parameter input validation;
• dependency injection with compile-time graph validation and scoped resolution;
• execution plans, direct invocation and optional monotonic deadlines;
• protocol-neutral policies, principals and scope evaluation;
• canonical Success / Failure outcomes with stable failure codes;
• protocol-neutral introspection snapshots and explicit discovery visibility;
• structured execution telemetry hooks with per-invocation identity.

What it does not include

The HTTP/ASGI, OpenAPI, MCP, CLI and OpenTelemetry functionality lives in separate distributions -- agnara-http, agnara-mcp, agnara-cli and agnara-telemetry -- and is not bundled into this standard-library-only kernel. Each is versioned in step with this one; check its PyPI project page for the versions available to install. Events and A2A remain zero-API reserved namespaces.

Frozen value semantics

Core value types such as CapabilityId and CapabilityDefinition are immutable and slotted. Assigning or deleting either a declared field or an unknown attribute raises dataclasses.FrozenInstanceError; a typo never attaches new state and does not leak CPython's internal slots error.

Confirmation boundary

Capabilities declared with confirmation="required" need an application-provided ConfirmationVerifier when their ExecutionPlan is compiled. Each invocation may carry an explicit opaque ConfirmationEvidence on ExecutionContext; values in generic invocation metadata are not approval.

The verifier receives the exact capability id, invocation, and principal and owns authenticity, input canonicalization, expiry, and replay protection. Missing evidence terminates execution with an interaction request. Rejected evidence terminates it as forbidden. Both outcomes occur before dependency construction or handler effects, and invoke_result() maps them to stable protocol-neutral failure codes.

Telemetry hooks

The core port is agnara.execution.TelemetryHook, with synchronous on_invocation_start(InvocationStartEvent) and on_invocation_terminal(InvocationTerminalEvent) callbacks. Register observers with ExecutionPlan.compile(definition, registry, hooks=[observer]); inheriting from the protocol is optional. Events expose capability, invocation and tracking identity; terminal events also contain monotonic duration and execution outcome, without handler inputs, returned payloads or exception objects.

Both plan construction paths copy the hook collection to a tuple. Missing or non-callable callbacks, coroutine functions and generator functions fail at startup with DefinitionError. Valid callbacks accept one event, return None synchronously and must not block. Their ordinary exceptions are ignored during execution.

Observers own synchronization of their mutable state and must keep their callbacks stable after compilation. Tracking IDs are caller-provided and may repeat; they are not unique span identifiers and should contain no secrets. Exporter startup, flushing and shutdown belong to adapters, not the core runtime. The separate agnara-telemetry package provides metrics and tracing hooks over an application-supplied meter and tracer.

Identity: code constructing InvocationStartEvent or InvocationTerminalEvent supplies invocation_id. Use the same identity for matching start and terminal events; tracking_id is not unique. Hooks that only read events are unaffected, and plans without hooks skip event construction entirely.

Links

• Source, architecture and decision records: https://github.com/Blandskron/agnara
• Changelog: https://github.com/Blandskron/agnara/blob/main/CHANGELOG.md
• Architecture: https://github.com/Blandskron/agnara/blob/main/ARCHITECTURE.md
• Longer example: https://github.com/Blandskron/agnara/blob/main/examples/quickstart.py

License

Apache License 2.0.