Invar

<p align="center"> <img src="docs/logo.svg" alt="Invar Logo" width="128" height="128"> </p> <h1 align="center">Invar</h1> <p align="center"> <strong>From AI-generated to AI-engineered code.</strong> </p> <p align="center"> Invar brings decades of software engineering best practices to AI-assisted development.<br> Through automated verification, structured workflows, and proven design patterns,<br> agents write code that's correct by construction—not by accident. </p> <p align="center"> <a href="https://badge.fury.io/py/invar-tools"><img src="https://badge.fury.io/py/invar-tools.svg" alt="PyPI version"></a> <a href="https://www.python.org/downloads/"><img src="https://img.shields.io/badge/python-3.11+-blue.svg" alt="Python 3.11+"></a> <a href="#license"><img src="https://img.shields.io/badge/License-Apache%202.0%20%2B%20GPL--3.0-blue.svg" alt="License"></a> </p> <p align="center"> <a href="#why-invar"><img src="https://img.shields.io/badge/🤖_Dogfooding-Invar's_code_is_100%25_AI--generated_and_AI--verified_using_itself-8A2BE2?style=for-the-badge" alt="Dogfooding"></a> </p>

What It Looks Like

An AI agent, guided by Invar, writes code with formal contracts and built-in tests:

from invar_runtime import pre, post

@pre(lambda items: len(items) > 0)
@post(lambda result: result >= 0)
def average(items: list[float]) -> float:
    """
    Calculate the average of a non-empty list.

    >>> average([1.0, 2.0, 3.0])
    2.0
    >>> average([10.0])
    10.0
    """
    return sum(items) / len(items)

Invar's Guard automatically verifies the code—the agent sees results and fixes issues without human intervention:

$ invar guard
Invar Guard Report
========================================
No violations found.
----------------------------------------
Files checked: 1 | Errors: 0 | Warnings: 0
Contract coverage: 100% (1/1 functions)

Code Health: 100% ████████████████████ (Excellent)
✓ Doctests passed
✓ CrossHair: no counterexamples found
✓