legaldown-validator 📐

The reference implementation of LegalDown

Parse, validate, and serialize LegalDown documents — from the command line or from Python.

Targets specification v0.2 · Every diagnostic carries a stable rule id · One dependency: PyYAML

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What it does

LegalDown is an open plain-text standard for legal documents. This package is the toolkit for working with those documents in code:

📥 Parses a .lgd file into a typed document model — frontmatter, sections, blocks, parties, definitions, anchors.

✅ Validates it against the specification's rule set (§16): broken cross-references, undefined terms, duplicate identifiers, malformed party metadata, bad dates and money values, and more.

📤 Serializes the model back to LegalDown source, so you can edit documents programmatically and write them out again.

🏷️ Names every finding. Each diagnostic carries the specification's stable rule id (§16.1) alongside its severity and message, so you can suppress one check, escalate another, or gate a build on exactly the rules you care about. Rule ids survive specification renumbering — they are the part of a diagnostic that is safe to depend on.

Install

pip install legaldown-validator

Python 3.11 or newer. The distribution is named legaldown-validator; the import name is legaldown:

import legaldown

The package ships a py.typed marker, so type checkers use its annotations directly.

Quick start

Given a LegalDown document:

---
title: Services Agreement
document_type: contract
sides:
  - name: providers
    label: Provider
    parties:
      - name: acme
        label: Acme
        type: legal_entity
        legal_name: Acme Corporation
  - name: clients
    label: Client
    parties:
      - name: beta
        label: Beta
        type: legal_entity
        legal_name: Beta Industries Inc.
language: en
---

# Fees {#fees}

{{party: beta}} shall pay {{money: 5000}} under {{ref: payment-terms}}.

Validate it:

legaldown validate contract.lgd

contract.lgd: error: [ref-broken] Broken section reference: 'payment-terms'.
contract.lgd: warning: [money-missing-currency] Money directive without currency parameter.

1 error(s), 1 warning(s), 0 info(s)

One diagnostic per line, each prefixed with its rule id. A clean document reports No issues found. and exits 0.

Diagnostics go to stdout; the trailing summary and No issues found. go to stderr, so legaldown validate contracts/ > report.txt captures the findings alone. --quiet drops the summary entirely.

Command line

legaldown validate contract.lgd                      # one document
legaldown validate contracts/                        # a whole directory, recursively
legaldown validate --format json contract.lgd        # machine-readable output
legaldown validate --ignore def-unreferenced doc.lgd # mute one rule
legaldown validate --warnings-as-errors doc.lgd      # tighten a CI gate
legaldown validate --final signed-contract.lgd       # nothing left to fill in

Option	Effect
--format {text,json}	Output format (default text)
--ignore RULE_ID	Suppress a rule by its stable id — repeatable
--final	Check a document is ready for signature: a remaining placeholder, drafting note, or template construct is an error (§15.9)
--warnings-as-errors	Report warnings at error severity
--strict	Exit non-zero on any diagnostic, not just errors
--quiet	Drop the trailing summary line

Directories are searched recursively for *.lgd, *.legaldown, and *.legal.md, and legaldown --version reports the validator version.

Exit codes: 0 clean · 1 diagnostics found (errors, or any diagnostic under --strict) · 2 a file could not be read.

JSON output

--format json emits the structured shape described in §16.9 — ideal for CI annotations, editor integrations, and dashboards:

{
  "legaldown_spec": "0.2",
  "validator_version": "0.2.0",
  "diagnostics": [
    {
      "file": "contract.lgd",
      "rule": "ref-broken",
      "level": "error",
      "message": "Broken section reference: 'payment-terms'."
    }
  ]
}

In CI

- run: pip install legaldown-validator
- run: legaldown validate contracts/ --warnings-as-errors

The exit code fails the job; the rule ids let you grant exceptions without turning whole checks off.

Python API

Three functions cover the common path:

from legaldown import parse_document, validate_document, serialize_document

document = parse_document(open("contract.lgd").read(), filename="contract.lgd")
result = validate_document(document)

for diagnostic in result.diagnostics:
    print(diagnostic.level, diagnostic.rule, diagnostic.message)

if result.is_valid:                      # no Error-level diagnostics
    print(serialize_document(document))

Working with the result

Validating a document builds the indices the checks need — section numbers, resolved definitions, party display text, every inline value found in the body. ValidationResult hands all of it back, so a renderer or a UI can reuse the work instead of re-deriving it:

Attribute	Contents
diagnostics	Diagnostic(rule, level, message) — the authoritative record
is_valid	True when no Error-level diagnostic was reported
errors / warnings / infos	Message strings by severity
rules(level=None)	Set of rule ids present, optionally filtered by severity
sections, section_lookup	Numbered section index; resolves {{ref:}} targets. Numbers count from the shallowest heading level, and a level a heading skips counts as 1 (#, ###, ## → 1, 1.1.1, 1.2), so no two sections share a number except alternatives and what they contain (§15.8)
definition_lookup, party_lookup, side_lookup, attachment_lookup	Resolved display text
inline_dates, inline_money, inline_durations, inline_fields, inline_placeholders	Field-spec values found in the body

Reading and editing the document model

parse_document returns a Document of plain dataclasses — Metadata, Section, Block, Side, Party, Attachment — that you can inspect, edit, and write back out:

from legaldown import parse_document, serialize_document

document = parse_document(source)
document.metadata.governing_law = "Czech Republic"

with open("contract.lgd", "w", encoding="utf-8") as handle:
    handle.write(serialize_document(document))

Content before the first heading — typically the sentence identifying the parties — is the document's preamble (§4.4): it is unnumbered, so it lives in document.preamble rather than in sections. document.iter_blocks() walks every body block, preamble first.

A Section's identifier is the explicit {#id} written after its heading, or "" when it has none. The identifiers the validator generates (§5.3, §5.5) are not written back into the model: read them from ValidationResult.sections.

document_to_dict() / document_from_dict() round-trip the model through JSON-friendly structures, except the two fields that describe the parsed source rather than the document, Metadata.not_line_editable and Metadata.frontmatter_absent. render_block() renders a single block when you are driving your own layout. iter_directives() lexes the directives in a piece of text by the §11.2 grammar — parameters in any order, quoted values decoded — and is what the validator itself uses.

One guarantee worth knowing: the parser is faithful — it never rewrites your input to make it valid, so what you authored is exactly what the validator judges. The serializer, by contrast, normalizes: frontmatter is re-emitted as canonical YAML, paragraphs are written as single lines, setext (underlined) headings are written as # headings, list items are written with - (+ where - would read as a thematic break) or 1., 2., … whichever marker they had, and table rows are written with a pipe at each end and every | in a cell escaped as \|, so expect a formatting-normalized file rather than a byte-for-byte copy.

Tables follow GFM: a table needs a delimiter row with one cell per header, rows take the header's width, and a | inside a cell — a code span's included — is written \|. A table block's headers and rows hold the cell text with those escapes removed, and align holds each column's alignment ("left", "right", "center", or "").

Lines indented four or more columns are an indented code block, as in CommonMark, so a paragraph indented that far is code: its directives and anchors are literal (§11.4). A paragraph that a model holds but that would, written at the margin, open a heading, a fence, or an HTML block is written with a backslash before it.

Raw HTML follows CommonMark's HTML blocks: a block of raw HTML, or an HTML comment on lines of its own, is an html block holding its source as written. No heading, directive, or anchor inside it is recognized (§8.6, §11.4), so a clause commented out with <!-- … --> is not a section. As in CommonMark, a comment left unclosed runs to the end of the document.

What gets checked

The full rule set with severities and examples lives in the specification (§16); this is the map:

Area	Checks include
Structure	Heading depth and skipped levels, hardcoded section numbers, missing title
Directive syntax	Malformed directives, repeated parameters, parameters a directive does not define, unquoted values that begin with a curly quote, stray {{
Cross-references	{{ref:}} targets that do not exist or point at an attachment
Anchors	Duplicate identifiers, malformed identifiers, auto-generated collisions and lost letters, markers outside an anchor position
Definitions	Undefined {{term:}}, duplicate ids, auto-generated ids that lost letters, missing quoted span, ambiguous quoting, unreferenced definitions
Parties and sides	Unknown {{party:}} / {{side:}}, malformed or duplicate names, invalid party types, minimum party and side counts, empty representatives
Values	Invalid dates, money without currency or with an unknown one, invalid durations and units, undeclared or reserved custom field types
Placeholders	Malformed ids, invalid types, one blank with two types, currencies, or units, placeholders in structural and format-checked frontmatter fields
Templates	Malformed question declarations and defaults, placeholders that contradict their declared question, invalid or contradictory conditions, references whose target a condition can remove, identifiers shared by units that can appear together, {{choose:}} that misses or invents an answer, definitions inside drafting notes and mistyped [!DRAFTING] markers, blanks in a defined term or against Markdown punctuation, fragments included twice; with --final, anything left unfilled
Attachments	Undeclared {{attach:}}, duplicate or colliding ids, empty titles, unreferenced attachments
Amendments	Terms the amended original does not define, definition overrides, empty amendment titles
Metadata	No frontmatter at all, invalid document type, invalid dates, missing sides, issuer side requirements, empty supersedes title, a declared legaldown version newer than 0.2

Each check reports at the severity the specification assigns it — Error, Warning, or Info.

Scope

This implementation claims Level 1 — Core (§17.2): everything above applies to a single document, in memory, with no filesystem access beyond reading the file you point it at. That covers authoring, editing, and CI validation of individual documents.

It is verified against the specification's own fixtures corpus — every rule it implements passes, bar seven whose fixtures span several files and are covered by unit tests instead. The specification (§17.5) requires an implementation to be explicit about the checks it does not perform, so those are listed in CONFORMANCE.md rather than left to be discovered.

Development

git clone https://github.com/ForLegalAI/legaldown-validator
cd legaldown-validator
pip install -e ".[dev]"
pytest

Conformance suite

The fixtures corpus lives in the specification repository, so point the harness at a checkout:

git clone https://github.com/ForLegalAI/LegalDown ../LegalDown
LEGALDOWN_FIXTURES_DIR=../LegalDown/fixtures pytest tests/conformance -q

Cases for rules outside Core are skipped and named, so the run doubles as the coverage ledger in CONFORMANCE.md, which accounts for every skip. CI runs it on every push and pull request.

Bug reports and pull requests are welcome in Issues; questions about the format itself belong in the specification repository's Discussions.

License

MIT — see LICENSE. The LegalDown specification itself is published separately under CC BY 4.0; it permits implementations to choose their own license.