mcp-business-docs

An MCP server that gives Claude Desktop — or any MCP client — read access to an invoice ledger, plus OCR over local documents.

Most published MCP servers expose tools and stop there. This one implements all three primitives, because they do different jobs:

What's exposed

Tools — search_invoices, get_invoice, vat_summary, ocr_document

Resources — invoice://list (browsable table), invoice://{invoice_id} (one invoice as markdown, addressable by id)

Prompts — chase_overdue(days), reconcile(invoice_id)

Related MCP server: mcp-ledger-server

Install into Claude Desktop

pip install -r requirements.txt

Then add to claude_desktop_config.json — macOS: ~/Library/Application Support/Claude/claude_desktop_config.json

{
  "mcpServers": {
    "business-docs": {
      "command": "python",
      "args": ["-m", "mcp_business_docs.server"],
      "env": { "PYTHONPATH": "/absolute/path/to/mcp-business-docs/src" }
    }
  }
}

Restart Claude Desktop. The tools appear under the connectors icon; invoice://list appears as an attachable resource.

For Claude Code:

claude mcp add business-docs -- python -m mcp_business_docs.server

Add a demo GIF here. Record Claude Desktop actually calling search_invoices and attaching invoice://list. It's the single most convincing thing this README can contain, and it takes two minutes with any screen recorder.

Tool descriptions are prompt engineering

The model never sees your implementation — only the name, the docstring, and the parameter schema. That makes the docstring the highest-leverage code in the repo. Two habits that measurably help:

State the boundary, not just the capability. search_invoices says it covers issued invoices only and excludes drafts and credit notes. Most tool-selection errors come from the model not knowing where a tool stops.

Return errors the model can act on. get_invoice("INV-0000") returns the known ids rather than raising. A thrown exception ends the turn; a structured error lets the model correct itself on the next one.

Try it

pip install -r requirements.txt
python -m mcp_business_docs.server     # stdio; Ctrl-C to stop
pytest tests/ -q

The store is seeded with four fabricated invoices. Swap store.py for a real database and nothing in server.py changes — which is the argument for keeping the protocol layer thin.

Security note

ocr_document reads a local path and returns its text. That text is untrusted: a scanned document can contain instruction-shaped strings aimed at whatever model reads it. The tool labels its output as data, but a client that concatenates tool results into a prompt without delimiting them is still exposed. Treat OCR output as hostile input, not as context.

Layout

src/mcp_business_docs/
  server.py   Tools, resources, and prompts
  store.py    SQLite-backed sample data
tests/        Logic tests that don't need a live client

License

MIT