---
id: nab-resolver
version: "0.0.14"
license: MIT
license_treatment: permissive
maintenance: active
---

# nab-resolver — Generic PubGrub dependency-resolver core

License: permissive · Maintenance: active · Downloads: 422.3K/mo

## What it is and what it does

nab-resolver is a generic dependency-resolution engine built on PubGrub algorithms. It provides the core constraint-solving logic without any Python-specific knowledge, making it suitable for embedding in resolvers for any package ecosystem. The package exports a ResolverProvider protocol and a Resolver class that callers parameterize with their own domain logic—defining how to fetch versions, check compatibility, and report requirements.

It is intended as a library for developers building package resolvers, not as a standalone tool. The Python-specific provider lives in nab-provider, and the user-facing CLI is in nab. The resolver itself is a SAT-style solver core: you supply it with a protocol implementation, and it returns a solution or raises ResolutionError. It has no runtime dependencies beyond the standard library.

Use it for:

- Embed the resolver in a custom package manager for a non-Python ecosystem.
- Build a dependency resolver for a domain-specific package format or language.
- Implement version constraint solving in a build tool or deployment system.
- Test or prototype dependency-resolution algorithms without writing a full resolver from scratch.

## Worth the install?

AI-flagged interpretation of the facts above — verify before relying.

A generic PubGrub-style dependency resolver core that accepts a ResolverProvider protocol, with no Python-specific logic—designed for embedding in package resolvers or other systems that need SAT-style constraint solving.

Yes, if you are building a package resolver or constraint-satisfaction system. The low install friction, zero runtime dependencies, active maintenance, and permissive license make it a solid foundation. Not relevant for end users of Python packages—use nab or nab-provider instead.

## Install

pip install nab-resolver
uv add nab-resolver
poetry add nab-resolver

## Installing nab-resolver

Before you install: Low friction: pure Python, no runtime dependencies, and actively maintained with a recent release. Supports Python 3.10 through 3.14.

License in practice: MIT license permits unrestricted use, modification, and distribution with minimal attribution requirements.

Quickstart:

from nab_resolver.resolver import Resolver, ResolverProvider
from nab_resolver.types import Term, Incompatibility

# Implement ResolverProvider with your domain logic
class MyProvider(ResolverProvider):
    def choose_package_version(self, term): ...
    def get_incompatibilities(self, term): ...

resolver = Resolver(MyProvider())
solution = resolver.resolve(root_term)

Requires Python 3.10 or later. Caller must implement the ResolverProvider protocol with domain-specific logic.

Verify before relying:

- Whether the resolver handles cyclic dependencies or other edge cases beyond what the public API documentation implies.
- Performance characteristics and scalability limits for large dependency graphs.

## Package facts

- License: MIT (permissive)
- Python support: supports_current
- Install friction: low
- Maintenance: active
- Downloads: 422.3K/month (top 15,000 on PyPI)
- Known vulnerabilities: none known

## Tags

dependency resolver library, pubgrub implementation, constraint satisfaction solver, package resolution engine, sat solver for dependencies, embeddable resolver core, version constraint solver, resolver-core, pubgrub, constraint-solver

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