solvi

Build decision systems from a catalog of Python functions and checks plus typed questions, and get answers you can verify.

Why

You describe a task with plain Python functions (computations, checks, answer rules) and questions with typed answers (yes/no, or a choice from a list). For each request, a strategist plans which functions and checks to run for the asked questions. Every answer comes with:

• a confidence (calibratable per question);
• a reason you can check: the rule inputs, a formula over computed facts, or a quote with character offsets in the source document;
• a hash-chained trace of every step, which can be re-executed later to confirm the answer or pinpoint the step that was altered.

When something cannot be computed, a function fails, or a rule returns an answer outside the allowed options, solvi abstains instead of guessing. A failed hard check always overrides any model confidence.

And it is fast. The strategist plans a flow over a 10 000-part catalog in about 6 ms and runs only the parts the questions need (2.4% of that catalog). Hard checks run first, so a failing one skips the expensive rest; independent slow parts (API calls, model inference) run in parallel. On an insurance-claim desk with slow services (examples/09_strategy_at_scale.py) a full decision takes 463 ms instead of 1 122 ms for a script that computes everything, and 152 ms when an expired policy settles the claim first.

Install

pip install solvi              # core: rules, checks, learned answer heads (numpy, scipy)
pip install "solvi[model]"     # + torch, transformers: ModernBERT field extractors for documents

Requires Python 3.10+.

Quickstart (core only, no model)

from datetime import date
from solvi import Answer, Catalog, Question, System

cat = Catalog()

@cat.fn                                            # argument names = facts it reads; function name = fact it sets
def days_requested(start, end):
    return (end - start).days + 1

@cat.fn
def remaining_after(balance, days_requested):
    return balance - days_requested

@cat.check(hard=True, then={"approve": "reject"})  # if this check is False, "approve" is forced to "reject"
def enough_balance(remaining_after):
    return remaining_after >= 0

@cat.check
def enough_notice(start, today, days_requested):
    return days_requested < 5 or (start - today).days >= 14

@cat.rule("approve")
def approve(enough_notice):
    return "approve" if enough_notice else "needs_manager"

system = System(cat, [Question("approve", "Approve the leave?",
                               Answer.choice(["approve", "needs_manager", "reject"]),
                               checkpoints=["enough_balance"])])
res = system.ask({"start": date(2026, 10, 19), "end": date(2026, 10, 23),
                  "today": date(2026, 9, 25), "balance": 14})
print(res["approve"].answer, res["approve"].confidence, res["approve"].why)
print(res.computed_state)
print(res.trace.replay(cat))

Output:

approve 1.0 enough_notice = True
days_requested           = 5
remaining_after          = 9
enough_balance           = True
enough_notice            = True
{'ok': True, 'steps': 5, 'mismatches': []}

With "balance": 3 the hard check fails and the answer is reject with status == "forced", whatever the rule says. solvi.show.show(res, cat) prints answers, the planned flow, the computed state and the replay result in one go.

How it works

• Catalog. @cat.fn (computation), @cat.check (bool), @cat.extract (value from text, returned as a Quote with offsets) and @cat.rule(question) (answer rule). A part's contract is its signature: argument names are the facts it reads, the function name is the fact it sets.
• Questions. Question(name, text, Answer.yes_no() | Answer.choice([...]), checkpoints=[...]). Questions without a rule get a small answer head trained from labeled examples (system.fit) or a readable learned rule list (system.learn_rule).
• Strategist. For each question it walks backwards from the rule's arguments (or the learned features) through the catalog signatures to the keys of init_state, adds the question's checkpoints and every check that touches a computed fact. Everything else in the catalog is not executed; the flow records why each part was taken or skipped.
• Execution. Each part runs once, even if several questions need it. Hard checks and their inputs run first; when one fails, the steps only the settled questions needed are skipped (res.trace.skipped). With System(..., workers=8) independent steps run in parallel threads as soon as their inputs are ready. Results go into computed_state with their provenance; extracted values keep their quote. Each step record is hashed and chained to the previous one in flow order, so the trace does not depend on scheduling.
• Answers and trace. res[q].answer / .confidence / .why / .status (ok, forced, abstain), plus res.trace.replay(catalog), which recomputes every step from recorded inputs and reports mismatches, broken hash links and quotes outside the text.

Extract from documents

With solvi[model], fields are found by a fine-tuned ModernBERT extractor. The extracted value is always a span of the document, so every answer built on it can be cited.

from solvi.extract_multi import MultiSpanExtractor

ex = MultiSpanExtractor(["total", "date"])          # ModernBERT-large, one pass per document for all fields
ex.fit(train_docs, train_spans, epochs=4)           # train_spans: [{"total": (start, end), "date": (start, end) | None}]
cat.extract(ex.field("total"))                      # doc -> Quote(text, start, end, confidence)
cat.extract(ex.field("date"))

@cat.fn
def amount(total):                                  # extracted values are strings; parse them in ordinary functions
    return float(total.replace(",", ""))

For long documents (contracts), solvi.extract_long.LongSpanExtractor reads the whole text in overlapping 1024-token windows, takes a field description instead of a fixed field list, and supports "no answer" with a per-field threshold. See docs/guide.md.

Results

Same training documents for both sides. The baseline, Laya, is a ModernBERT-large model that answers the typed questions directly, fine-tuned with its authors' recipe. Details and caveats: docs/benchmarks.md.

• Calibrated confidence: ECE 0.008 (SROIE), 0.011 (CORD), 0.027 (CUAD).
• On the document benchmarks, 100% of answers are backed by a quote at stated offsets, or the system abstains.
• Speed: about 0.4 ms per decision when no model is involved; about 39 ms per receipt with the one-pass extractor on an A100 GPU.

Speed

Strategist on random layered catalogs (benchmarks/strategist_scale.py, one CPU core):

Insurance claim desk with six slow services of 100-300 ms (examples/09_strategy_at_scale.py):

A rule-only decision on a small catalog takes well under a millisecond; on documents the extractor dominates (about 39 ms per receipt with the one-pass extractor on an A100).

When to use it

• The answer is a computation or a rule over a few values found in a document or a record: receipts, invoices, contracts, requests, orders.
• You need to show why: auditors, compliance, or a human reviewing low-confidence cases.
• Some rules are non-negotiable (hard checks), and the rest can be learned from about 100 labeled examples.

When not to use it

• Open-ended free-text questions or generated answers. solvi answers yes/no and choice questions only.
• New fields with no labeled examples. Extracting a field from its description alone does not work yet (14% and 66% on two held-out fields); a universal extractor is coming.
• No labels at all. Plan on roughly 100 labeled documents (field positions) per task.
• CPU-only deployment with a quantized model: the int8 ONNX extractor loses up to 12 points on amounts, company names and addresses. fp32 on CPU keeps accuracy but takes about 0.7 s per receipt on 2 cores.

Examples

Run them from a clone: python examples/01_leave_request.py.

More

• docs/guide.md: full API walkthrough.
• docs/benchmarks.md: setups, per-question numbers, caveats.
• benchmarks/: dataset loaders and benchmark scripts (SROIE, CORD, CUAD, Kleister-NDA).
• Tests: pytest.

License

Apache-2.0. See LICENSE.

Citation

A paper is in preparation. Until then, please cite the repository:

@software{solvi,
  title  = {solvi: verifiable decision systems from catalogs of functions and checks},
  author = {mxkuzn and solvi contributors},
  year   = {2026},
  url    = {https://github.com/solvi-ai/solvi}
}