Saos MCP Server

mcp-saos

Installation (one command)

Published on npm + the MCP Registry (io.github.matematicsolutions/mcp-saos). Run without cloning:

npx -y @matematicsolutions/mcp-saos

MCP client configuration (stdio):

{ "mcpServers": { "mcp-saos": { "command": "npx", "args": ["-y", "@matematicsolutions/mcp-saos"] } } }

(Building from source - below.)

An MCP (Model Context Protocol) server for Polish case law - a connector to SAOS (System Analizy Orzeczen Sadowych - the courts' public case-law database, run by Fundacja ePanstwo).

Part of the MateMatic "Polish legal AI" project. It runs as a separate process communicating over stdio; the chat template (a fork of mike) calls it through the MCP protocol.

What SAOS is

An open database of Polish court judgments. Public REST API, no key required.

Coverage caveat: coverage is broad and includes current judgments (2024-2026 are well populated), but it is uneven by court type, and some Supreme Court resolutions exist only as citations in other judgments. Verify anything critical against sn.pl, orzeczenia.ms.gov.pl, trybunal.gov.pl.

The database covers: common courts (COMMON), the Sad Najwyzszy (Supreme Court, SUPREME), the Trybunal Konstytucyjny (Constitutional Tribunal, CONSTITUTIONAL_TRIBUNAL), the KIO (National Appeal Chamber, NATIONAL_APPEAL_CHAMBER). Administrative courts (WSA/NSA) - no data in SAOS.

MCP tools

saos_cite_check - the citator

Give it a case number (a placeholder here; use a real one):

{ "caseNumber": "III CZP NN/RR" }

It searches SAOS full-text for later judgments citing that signature, scans their reasoning for departure phrases ("odstepuje od pogladu wyrazonego", "nie podziela pogladu", "traci moc uchwala", "uchwala skladu siedmiu sedziow" and others) within ~500 characters of the signature, and returns one of four verdicts: przelamanie_wykryte, uchwala_skladu_powiekszonego, nadal_cytowany, brak_cytowan_w_saos. Each hit includes a +-200 character fragment for human verification.

Every phrase on the list was verified against live SAOS data - the evidence table, the algorithm and the honest-limits section are in docs/CITE-CHECK.md. The short version: no hits does NOT mean the judgment is still good law, and every response says so.

Requirements

• Node.js >= 18
• npm >= 9
• Internet access (live API saos.org.pl)

Installation and build

git clone https://github.com/matematicsolutions/mcp-saos
cd mcp-saos
npm install
npm run build

After npm run build, the entry point is dist/index.js.

Standalone run (test)

node dist/index.js
# the server listens on stdin/stdout, diagnostic logs go to stderr

Wiring into the chat template (fork of mike) - mcp-servers.json

Add an entry to your client's MCP configuration (e.g. mcp-servers.json):

{
  "name": "saos",
  "transport": "stdio",
  "command": "node",
  "args": ["C:/Users/<YOUR-USER>/mcp-saos/dist/index.js"],
  "enabled": true
}

Provide the absolute path to dist/index.js. On Windows use forward slashes / or double backslashes \\.

Tests

npm run build
npm test            # offline: drift test + unit tests (parser, window scan, phrase patterns)
node test/smoke.mjs # live: 5 checks against the real SAOS API, including the citator

The smoke test checks tools/list (4 tools), search, search_by_case, a Constitutional Tribunal lookup and saos_cite_check on a Supreme Court resolution with known later treatment.

Architecture

stdin  -->  MCP JSON-RPC (stdio transport)  -->  src/index.ts
                                                      |
                                            SAOS REST API
                                     https://www.saos.org.pl/api
                                            /search/judgments
                                            /judgments/{id}
stdout <--  formatted text responses  <--

No external dependencies for HTTP/JSON - requests go through the built-in node:https. The only production dependency: @modelcontextprotocol/sdk.

Limitations and known pitfalls

• pageSize has a hard lower limit of 10 (SAOS returns HTTP 400 for less) - the server automatically enforces a minimum of 10.
• courtType=ADMINISTRATIVE returns empty results - SAOS does not index WSA/NSA.
• Dates in the database may contain OCR artifacts (e.g. "3013-12-04") - the case number is more reliable than the judgmentDate field.
• Coverage is uneven by court type - the server states the relevant caveats in every tool response.
• saos_cite_check is a heuristic. It reads the top citing judgments only, its phrase list cannot cover every way a court departs from a line of case law, and no hits does not confirm the judgment is current.

License

MIT - see the LICENSE file for details. Judgment data: Fundacja ePanstwo, open license (public API with no usage restrictions).

Part of the MateMatic legal stack

This server is one of five MCP connectors covering Polish jurisdiction + EU law, used by Patron (AGPL-3.0) and any other MCP-aware legal AI agent.

• mcp-saos (this repo) - common courts, Supreme Court, Constitutional Tribunal, KIO
• mcp-nsa - NSA + 16 WSA administrative courts
• mcp-isap - Polish legislation (Dz.U. + M.P.)
• mcp-krs - Polish company registry (KRS)
• mcp-eu-sparql - EU law + CJEU (EUR-Lex)

All five MCP servers share the same structuredContent.citations contract: each tool returns an array of {title, url, snippet?, ...metadata} that legal agents can render directly in their citation panel.

See matematicsolutions/.github for the full org profile.