sheet-compressor MCP Server

An MCP server that wraps the sheet-compressor library, exposing it to Claude Desktop / Claude Code over stdio. It demonstrates all three MCP primitives — Tool, Resource, Prompt — plus a stretch extract_orders tool that makes one Claude call on Bedrock to return schema-valid order JSON.

See docs/PRD.md for the full spec, CONTEXT.md for the domain vocabulary, and PRODUCTION.md for the enterprise path (transport, deploy, governance, observability, CI gates).

Install

Python 3.10+.

pip install -r requirements.txt
cp .env.example .env   # adjust LLM_PROVIDER / AWS_REGION / model ids

extract_orders needs AWS credentials in the standard chain (~/.aws/credentials, SSO, instance role) or — if you flip LLM_PROVIDER=anthropic — ANTHROPIC_API_KEY in your environment. The Core primitives (compress_spreadsheet, example_sheet, sheet_qa) make no LLM calls and need no credentials.

Related MCP server: mcp-data-lens

Register

Claude Desktop

mcp install server.py

Or hand-edit claude_desktop_config.json:

{
  "mcpServers": {
    "sheet-compressor": {
      "command": "python",
      "args": ["/absolute/path/to/server.py"],
      "env": {
        "LLM_PROVIDER": "bedrock",
        "AWS_REGION": "us-east-1",
        "BEDROCK_MODEL_ID": "anthropic.claude-haiku-4-5"
      }
    }
  }
}

Restart Claude Desktop and the tool, resource, and prompt appear in the client.

Claude Code

Add a .mcp.json at the repo root (or ~/.claude/mcp.json for global):

{
  "mcpServers": {
    "sheet-compressor": {
      "command": "python",
      "args": ["/absolute/path/to/server.py"],
      "env": {
        "LLM_PROVIDER": "bedrock",
        "AWS_REGION": "us-east-1",
        "BEDROCK_MODEL_ID": "anthropic.claude-haiku-4-5"
      }
    }
  }
}

Then /mcp inside Claude Code confirms sheet-compressor is connected and lists the three primitives + the stretch tool.

Demo

The demo runs against examples/northstar-auto-q3-2025.xlsx (the automotive hero file: regional dealer-group sales, deliberately messy — merged headers, stacked per-region tables, blank gaps). One-line summary, in the client:

Use sheet-compressor to compress examples/northstar-auto-q3-2025.xlsx, then use sheet_qa to tell me which region had the most orders, then run extract_orders on the same file and report the total revenue.

That asks the client to walk the three primitives in sequence:

1. compress_spreadsheet turns the hero file into the compact anchor encoding and returns its token figures.

2. sheet_qa wraps the encoding with the anchor reader explainer + the sheetQA task template so the model can decode the sheet and answer the region question from cell values — no extra LLM call from the server.

3. extract_orders compresses the sheet again and makes one Bedrock call with structured outputs to return {orders: [...], total_revenue}.

This is the flow the eval harness regression-tests, and the flow PRODUCTION.md describes hardening for enterprise deployment.

Tool — compress_spreadsheet

compress_spreadsheet(xlsx_path: str,
                     encoding: str = "anchor",
                     sheet: str | None = None) -> dict

Returns {encoding, compressed, tokenEstimate, rawBaselineTokens, savingsRatio}.

• encoding ∈ {anchor, invertedIndex, formatAggregation}. Default anchor is value-preserving and ships with a reader prompt — see ADR-0002.

• sheet selects a worksheet by name in a multi-sheet workbook.

Makes no LLM calls — the AI reasoning happens in the client.

Resource — sheet://examples/{name}

Returns the bundled example sheet in the default anchor encoding so a client can see the format before sending its own data. Known names: sample-orders (the generic order ledger). Unknown names return a clear ValueError.

Prompt — sheet_qa

sheet_qa(encoding_text: str, question: str, encoding: str = "anchor") -> str

Composes the encoding's reader explainer with the library's sheetQA task template, substituting {ENCODING} and {QUESTION}. Hand this back to the client and the model has everything it needs to decode the compressed sheet and answer the question — no extra round-trip through this server.

Stretch tool — extract_orders

extract_orders(xlsx_path: str, sheet: str | None = None) -> dict

Compresses xlsx_path (anchor encoding), then makes one Claude call — on Bedrock by default per ADR-0001 — with structured outputs, returning:

{
  "orders": [
    {order_id, order_date, dealership, region, make, model,
     qty, unit_price, total, status},
    ...
  ],
  "total_revenue": <number>
}

The provider is selected by LLM_PROVIDER (bedrock | anthropic); the model id is a config value — live-swap Haiku 4.5 → Opus 4.8 by editing the client's env block. This is the only place the server itself calls an LLM.

Tests

python -m pytest tests/

Tests run at Seam 1 (the tool functions) against both the bundled examples/sample-orders.xlsx ledger and the automotive hero file, and at Seam 2 (extract_orders against a fake LLM provider) — fully deterministic, no network. The upstream sheet-compressor library is left unmodified.

Eval harness

python -m sheet_compressor_mcp.evals

Golden cases over the hero file, scored against the real LLM provider (per .env — Bedrock primary, Anthropic-direct fallback). Network-dependent and separate from the unit suite. Prints [PASS] / [FAIL] per expectation with a final N/M expectations passed summary, and exits non-zero if any expectation failed (so a CI script can gate on it). The shipped suite checks coverage (all four regions present, ≥100 orders extracted), schema fidelity (every order has every required field; regions/makes drawn from the sheet's known sets), and totals consistency (total_revenue == sum of order totals).

Layout

server.py                 # MCP registration (FastMCP, stdio)
sheet_compressor_mcp/
  tools.py                # pure tool functions — tested directly
  extract.py              # extract_orders stretch tool
  llm.py                  # LLM provider abstraction (Bedrock + Anthropic)
  evals.py                # golden-case eval harness (real-provider)
examples/
  build_hero_file.py      # generator for the automotive hero file
  northstar-auto-q3-2025.xlsx
  build_ledger.py         # generator for the bundled generic ledger
  sample-orders.xlsx
tests/
  test_compress_spreadsheet.py
  test_example_sheet.py
  test_sheet_qa.py
  test_extract_orders.py
  test_evals.py
PRODUCTION.md             # the enterprise path — transport, deploy,
                          # governance, observability, CI eval gates