vekna

Run coding agents as rituals: ordinary Python programs whose steps you control and whose agent calls happen inside those steps. Agents run permissively within a step; determinism lives at the step boundaries.

Documentation is at vekna.fancysnake.dev.

Install

pip install vekna

Python 3.11+. Testing your rituals needs the trial extra: pip install 'vekna[trial]' — quoted, because zsh globs the brackets.

A ritual

Put a rituals.py in your project — or a rituals/ package, split however you like, once one file stops being enough:

from typing import Annotated

from pydantic import BaseModel, Field

from vekna.folio.coding import coding
from vekna.folio.shell import shell
from vekna.lexicon import Done, ritual, step


class FixTests(BaseModel):
    # A retry budget counts down to zero, so the CLI rejects a negative one
    # rather than letting `--bound -1` run until the step backstop.
    bound: Annotated[int, Field(ge=0)] = 3


class Attempt(BaseModel):
    left: int


class Verdict(BaseModel):
    outcome: str


# The return annotation is the step's exits: back to `fix`, or finished with a
# `Verdict`. mypy checks every return against it, so a mis-wire fails the type
# check rather than a cast.
@step
async def fix(state: Attempt) -> Attempt | Done[Verdict]:
    result = await shell("mise run test:py")
    if result.exit_code == 0:
        return Done(Verdict(outcome="green"))
    if state.left <= 0:
        return Done(Verdict(outcome="gave up"))
    await coding(f"The test suite fails:\n{result.stdout}\nFix it.")
    return Attempt(left=state.left - 1)


# `def`, not `async def`: naming the first step has nothing to await. A step or
# entrypoint is written whichever way its body needs.
@ritual("fix_tests")
def fix_tests(components: FixTests) -> Attempt:
    return Attempt(left=components.bound)

Then cast it:

vekna cast fix_tests --bound 5

Output streams live as a tree of rites — one node per step, one nested under it per medium call, with the agent's own output indented beneath. The last line is the cast's result, as JSON:

result: {"outcome":"green"}

Claude Code plugin

The ritual-scribe skill teaches Claude Code to write rituals. Install it from this repo's marketplace:

claude plugin marketplace add fancysnake/vekna
claude plugin install ritual-scribe@vekna

Commands

Contributing

CONTRIBUTING.md covers setup, the check loop, where code goes, and pull requests. docs/README.md is where the ideas live.

Licence

BSD-3-Clause.