DecisionKit

DecisionKit is a lightweight explainable scoring and ranking engine for Python backends.

Describe criteria, weights, constraints, penalties, and bonuses — in code or config — then get ranked alternatives with scores, human-readable explanations, and audit-ready output.

No machine learning. No database. No web UI. Core has zero runtime dependencies.

Project status

Beta (v0.3.1) — useful for real backend workflows; API aims to stay stable across minor releases. See CHANGELOG.md.

Installation

pip install decisionkit

Optional YAML support:

pip install "decisionkit[yaml]"

From source:

pip install -e ".[dev]"

Quick start

from decisionkit import DecisionModel, Criterion

model = DecisionModel(
    criteria=[
        Criterion("relevance", weight=0.5, direction="max"),
        Criterion("rating", weight=0.3, direction="max"),
        Criterion("workload", weight=0.2, direction="min"),
    ],
    method="weighted_sum",
    explain=True,
)

result = model.rank([
    {"id": "reviewer_1", "relevance": 0.92, "rating": 4.8, "workload": 7},
    {"id": "reviewer_2", "relevance": 0.81, "rating": 4.5, "workload": 2},
])

print(result.best.id)
print(result.explain())

Config-driven usage

from decisionkit import DecisionModel

config = {
    "method": "weighted_sum",
    "explain": True,
    "criteria": [
        {"name": "relevance", "weight": 0.5, "direction": "max"},
        {"name": "rating", "weight": 0.3, "direction": "max"},
        {"name": "workload", "weight": 0.2, "direction": "min"},
    ],
    "constraints": [
        {
            "name": "available_only",
            "field": "available",
            "operator": "eq",
            "value": True,
            "reason": "Reviewer must be available",
        }
    ],
    "penalties": [
        {
            "name": "high_workload_penalty",
            "field": "workload",
            "operator": "gt",
            "value": 5,
            "amount": 0.1,
        }
    ],
    "bonuses": [
        {
            "name": "exact_topic_bonus",
            "field": "topic_match",
            "operator": "gte",
            "value": 0.9,
            "amount": 0.05,
        }
    ],
}

model = DecisionModel.from_dict(config)
result = model.rank(
    [
        {
            "id": "reviewer_1",
            "relevance": 0.92,
            "rating": 4.8,
            "workload": 7,
            "available": True,
            "topic_match": 0.95,
        },
        {
            "id": "reviewer_2",
            "relevance": 0.81,
            "rating": 4.5,
            "workload": 2,
            "available": True,
            "topic_match": 0.8,
        },
    ],
    context={"max_workload": 5},
)

print(result.best.id)
print(result.to_audit_dict(include_hash=True)["audit_hash"])

JSON and optional YAML helpers:

model = DecisionModel.from_json(model.to_json())
# pip install "decisionkit[yaml]"
# model = DecisionModel.from_yaml(model.to_yaml())

Rules: constraints, penalties, bonuses

Operators: eq, ne, gt, gte, lt, lte, in, not_in, contains, between.

Context-aware rule:

{
    "name": "within_capacity",
    "field": "workload",
    "operator": "lte",
    "context": "max_workload",
}

Compound rule (all = AND, any = OR):

{
    "name": "eligible",
    "all": [
        {"field": "available", "operator": "eq", "value": True},
        {"field": "workload", "operator": "lte", "context": "max_workload"},
    ],
}

Audit export and hash

audit = result.to_audit_dict(
    decision_id="req-123",
    metadata={"tenant": "acme"},
    timestamp="2026-07-10T10:00:00Z",
    include_hash=True,
)
digest = result.audit_hash()  # sha256 of canonical decision payload

The digest covers method, model, context, inputs, exclusions, ranking, and best alternative. It excludes decision_id, metadata, and timestamp by default. Details: docs/audit.md.

FastAPI integration

from fastapi import FastAPI, HTTPException
from decisionkit import DecisionModel, ValidationError

app = FastAPI()

@app.post("/rank")
def rank(payload: dict):
    try:
        model = DecisionModel.from_dict(payload["model"])
        result = model.rank(
            payload["alternatives"],
            context=payload.get("context", {}),
        )
        return result.to_audit_dict(
            decision_id=payload.get("decision_id"),
            include_hash=True,
        )
    except ValidationError as exc:
        raise HTTPException(status_code=400, detail=str(exc)) from exc

See examples/fastapi_example.py.

Django service-layer integration

Keep DecisionKit in a service module; store config in settings/admin/DB:

from decisionkit import DecisionModel

def rank_reviewers(candidates: list[dict], model_config: dict) -> dict:
    model = DecisionModel.from_dict(model_config)
    result = model.rank(candidates, context={"max_workload": 5})
    return result.to_audit_dict(decision_id="editorial-assign", include_hash=True)

See examples/django_service_example.py.

How DecisionKit compares

Approach	Fit
Ad-hoc if / spreadsheet scoring	Fast to start, hard to explain, test, or reuse
Generic rule engines	Great for branching logic; weaker at weighted ranking + score breakdowns
Academic MCDA toolkits	Broad method coverage; often awkward for backend APIs and audits
DecisionKit	Backend-friendly weighted ranking with rules, explanations, and audit hashes

DecisionKit is not trying to replace every MCDA method. It focuses on explainable scoring you can ship in Django/FastAPI services.

Supported methods

Method	Key	Notes
Weighted sum	weighted_sum	Min-max normalization relative to the evaluated alternatives; min criteria inverted
TOPSIS	topsis	Vector normalization + closeness to ideal

Scores and “strong/weak” explanation labels are relative to the current alternative set, not absolute universal grades.

Examples

python examples/reviewer_selection.py
python examples/vendor_ranking.py
python examples/task_prioritization.py
python examples/risk_scoring.py
python examples/django_service_example.py

More: docs/examples.md

Documentation

• docs/index.md — docs home
• docs/quickstart.md
• docs/rules.md
• docs/audit.md
• docs/api-reference.md

Development

pip install -e ".[dev]"
python -m ruff check src tests examples
python -m mypy src
python -m pytest --cov=decisionkit --cov-report=term-missing

CI runs on Python 3.11 and 3.12 (see .github/workflows/ci.yml).

Release steps: RELEASE.md

Roadmap

v0.4.0

• AHP method (optional, still backend-friendly)
• Nested boolean rule trees (beyond flat all/any)
• Signed / hashed decision record helpers for long-term storage

Later

• ELECTRE / PROMETHEE (only if API stays simple)
• decisionkit-django integration package
• Optional CLI for batch ranking

License

MIT — see LICENSE.