Spreadsheet MCP

MCP server for spreadsheet analysis and editing. Slim, token-efficient tool surface designed for LLM agents.

Why?

Dumping a 50,000-row spreadsheet into an LLM context is expensive and usually unnecessary. Most spreadsheet tasks need surgical access: find a region, profile its structure, read a filtered slice. This server exposes tools that let agents discover → profile → extract without burning tokens on cells they don't need.

• Full support: .xlsx, .xlsm (via umya-spreadsheet)
• VBA source inspection (optional): .xlsm via SPREADSHEET_MCP_VBA_ENABLED=true / --vba-enabled (parses embedded xl/vbaProject.bin via ovba)
• Discovery only: .xls, .xlsb (enumerated, not parsed)

Architecture

• LRU cache keeps recently-accessed workbooks in memory (configurable capacity)
• Lazy sheet metrics computed once per sheet, reused across tools
• Region detection on demand runs for sheet_overview and is cached for region_id lookups (find_value, read_table, table_profile)

Tool Surface

VBA Support (Read-Only)

VBA tools are disabled by default. When enabled, the server can extract and parse the embedded VBA project from .xlsm files and return module source code.

Enable via:

• CLI: --vba-enabled
• Env: SPREADSHEET_MCP_VBA_ENABLED=true

Tools:

• vba_project_summary: Lists modules + basic project metadata
• vba_module_source: Returns paged source for a single module

Notes:

• This does not execute macros; it only reads and returns text.
• Responses are size-limited; page through module source.

Write & Recalc Support

Write tools allow "what-if" analysis: fork a workbook, edit cells, recalculate formulas via LibreOffice, and diff the results. For safety, you can create checkpoints for high‑fidelity rollback and apply previewed (staged) changes explicitly.

Enabling Write Tools

Always use the :full Docker image for write/recalc features:

docker run -v /path/to/workbooks:/data -p 8079:8079 ghcr.io/psu3d0/spreadsheet-mcp:full

The Docker image includes LibreOffice with pre-configured macros required for reliable recalculation. Running outside Docker requires manual LibreOffice setup (macro trust, headless config) and is not recommended.

Write Tools

Token-Efficient Write Workflows

find_formula paging

{
  "tool": "find_formula",
  "arguments": {
    "workbook_or_fork_id": "wb-23456789ab",
    "sheet_name": "Calc",
    "query": "SUM(",
    "include_context": false,
    "limit": 20,
    "offset": 0
  }
}

get_changeset summary + filters

{
  "tool": "get_changeset",
  "arguments": {
    "fork_id": "fork-23456789abcd",
    "summary_only": true,
    "exclude_subtypes": ["recalc_result"],
    "limit": 200,
    "offset": 0
  }
}

Docker Paths (Exports + Screenshots)

When running in Docker with --workspace-root /data and a host mount like -v /path/to/workbooks:/data:

• Fork working files live under /tmp/mcp-forks inside the container (not visible on host).
• save_fork.target_path is resolved under workspace_root (Docker default: /data). Use a relative path like out.xlsx (or exports/out.xlsx) to write back into the mounted folder on the host.
• screenshot_sheet writes PNGs under screenshots/ in workspace_root (Docker default: /data/screenshots/).

Screenshot Tool

screenshot_sheet captures a visual PNG of a rectangular range, rendered headless via LibreOffice in the :full image. The PNG is auto‑cropped to remove page whitespace and saved under screenshots/ in the workspace. Note: the tool returns a file:// URI on the server filesystem; when running via Docker, treat it as a container path and look for the PNG under your mounted workspace folder (e.g. screenshots/<name>.png).

Arguments:

• workbook_or_fork_id (required; accepts a workbook_id or fork_id)
• sheet_name (required)
• range (optional, default A1:M40)

Limits and behavior:

• Max range per screenshot: 100 rows × 30 columns. If exceeded, the tool fails with suggested tiled sub‑ranges to request instead.
• After export/crop, a pixel guard rejects images that are too large for reliable agent use (default max 4096px on a side or 12MP area). On rejection, the tool returns smaller range suggestions.
• Override pixel guard via env vars: SPREADSHEET_MCP_MAX_PNG_DIM_PX, SPREADSHEET_MCP_MAX_PNG_AREA_PX.

See docs/RECALC.md for architecture details.

Example

Request: Profile a detected region

{
  "tool": "table_profile",
  "arguments": {
    "workbook_id": "wb-23456789ab",
    "sheet_name": "Q1 Actuals",
    "region_id": 1,
    "sample_size": 10,
    "sample_mode": "distributed"
  }
}

Response:

{
  "sheet_name": "Q1 Actuals",
  "headers": ["Date", "Category", "Amount", "Notes"],
  "column_types": [
    {"name": "Date", "inferred_type": "date", "nulls": 0, "distinct": 87},
    {"name": "Category", "inferred_type": "text", "nulls": 2, "distinct": 12, "top_values": ["Payroll", "Marketing", "Infrastructure"]},
    {"name": "Amount", "inferred_type": "number", "nulls": 0, "min": 150.0, "max": 84500.0, "mean": 12847.32},
    {"name": "Notes", "inferred_type": "text", "nulls": 45, "distinct": 38}
  ],
  "row_count": 1247,
  "samples": [...]
}

The agent now knows column types, cardinality, and value distributions—without reading 1,247 rows.

Recommended Agent Workflow

1. list_workbooks → list_sheets → workbook_summary for orientation
2. sheet_overview to get detected_regions (ids/bounds/kind/confidence)
3. table_profile → read_table with region_id, small limit, and sample_mode (distributed preferred)
4. Use find_value (label mode) or range_values for targeted pulls
5. Reserve sheet_page for unknown layouts or calculator inspection; prefer compact/values_only
6. Keep payloads small; page/filter rather than full-sheet reads

Region Detection

Spreadsheets often contain multiple logical tables, parameter blocks, and output areas on a single sheet. The server detects these automatically:

1. Gutter detection — Scans for empty rows/columns that separate content blocks
2. Recursive splitting — Subdivides large areas along detected gutters
3. Border trimming — Removes sparse edges to tighten bounds
4. Header detection — Identifies header rows (including multi-row merged headers)
5. Classification — Labels each region: data, parameters, outputs, calculator, metadata
6. Confidence scoring — Higher scores for well-structured regions with clear headers

Regions are cached per sheet. Tools like read_table accept a region_id to scope reads without manually specifying ranges.

Quick Start

Docker (Recommended)

Two image variants are published:

# Read-only (slim image)
docker run -v /path/to/workbooks:/data -p 8079:8079 ghcr.io/psu3d0/spreadsheet-mcp:latest

# Read-only + VBA tools enabled
docker run -v /path/to/workbooks:/data -p 8079:8079 -e SPREADSHEET_MCP_VBA_ENABLED=true ghcr.io/psu3d0/spreadsheet-mcp:latest

# With write/recalc support (full image)
docker run -v /path/to/workbooks:/data -p 8079:8079 ghcr.io/psu3d0/spreadsheet-mcp:full

Cargo Install

# Read-only
cargo install spreadsheet-mcp
spreadsheet-mcp --workspace-root /path/to/workbooks

# Enable VBA tools
SPREADSHEET_MCP_VBA_ENABLED=true spreadsheet-mcp --workspace-root /path/to/workbooks

Note: For write/recalc features, use the :full Docker image instead of cargo install. The Docker image includes LibreOffice with required macro configuration.

Build from Source

cargo run --release -- --workspace-root /path/to/workbooks

Default transport: HTTP streaming at 127.0.0.1:8079. Endpoint: POST /mcp.

Use --transport stdio for CLI pipelines.

MCP Client Configuration

Claude Code / Claude Desktop

Add to ~/.claude.json or project .mcp.json:

Read-only (slim image):

{
  "mcpServers": {
    "spreadsheet": {
      "command": "docker",
      "args": ["run", "-i", "--rm", "-v", "/path/to/workbooks:/data", "ghcr.io/psu3d0/spreadsheet-mcp:latest", "--transport", "stdio"]
    }
  }
}

Read-only + VBA tools enabled:

{
  "mcpServers": {
    "spreadsheet": {
      "command": "docker",
      "args": ["run", "-i", "--rm", "-v", "/path/to/workbooks:/data", "ghcr.io/psu3d0/spreadsheet-mcp:latest", "--transport", "stdio", "--vba-enabled"]
    }
  }
}

With write/recalc (full image):

{
  "mcpServers": {
    "spreadsheet": {
      "command": "docker",
      "args": ["run", "-i", "--rm", "-v", "/path/to/workbooks:/data", "ghcr.io/psu3d0/spreadsheet-mcp:latest-full", "--transport", "stdio", "--recalc-enabled"]
    }
  }
}

Binary (no Docker):

{
  "mcpServers": {
    "spreadsheet": {
      "command": "spreadsheet-mcp",
      "args": ["--workspace-root", "/path/to/workbooks", "--transport", "stdio"]
    }
  }
}

Cursor / VS Code

Read-only (slim image):

{
  "mcp.servers": {
    "spreadsheet": {
      "command": "docker",
      "args": ["run", "-i", "--rm", "-v", "${workspaceFolder}:/data", "ghcr.io/psu3d0/spreadsheet-mcp:latest", "--transport", "stdio"]
    }
  }
}

With write/recalc (full image):

{
  "mcp.servers": {
    "spreadsheet": {
      "command": "docker",
      "args": ["run", "-i", "--rm", "-v", "${workspaceFolder}:/data", "ghcr.io/psu3d0/spreadsheet-mcp:latest-full", "--transport", "stdio", "--recalc-enabled"]
    }
  }
}

Binary (no Docker):

{
  "mcp.servers": {
    "spreadsheet": {
      "command": "spreadsheet-mcp",
      "args": ["--workspace-root", "${workspaceFolder}", "--transport", "stdio"]
    }
  }
}

HTTP Mode

docker run -v /path/to/workbooks:/data -p 8079:8079 ghcr.io/psu3d0/spreadsheet-mcp:latest

Connect via POST http://localhost:8079/mcp.

Local Development

To test local changes without rebuilding Docker:

cargo build --release

Then point your MCP client to the binary:

{
  "mcpServers": {
    "spreadsheet": {
      "command": "/path/to/spreadsheet-mcp/target/release/spreadsheet-mcp",
      "args": ["--workspace-root", "/path/to/workbooks", "--transport", "stdio"]
    }
  }
}

Configuration

Performance

• LRU workbook cache — Recently opened workbooks stay in memory; oldest evicted when capacity exceeded
• Lazy metrics — Sheet metrics computed on first access, cached for subsequent calls
• Region detection on demand — Runs on sheet_overview (or region_id lookups) and is cached thereafter
• Sampling modes — distributed sampling reads evenly across rows without loading everything
• Output caps — sheet_overview truncates regions/headers by default; use tool params to request more
• Compact formats — values_only and compact output modes reduce response size

Testing

cargo test

Covers: region detection, region-scoped tools, read_table edge cases (merged headers, filters, large sheets), workbook summary.

Local MCP Testing

To test local changes with an MCP client (Claude Code, Cursor, etc.), use the helper script that rebuilds the Docker image on each invocation:

{
  "mcpServers": {
    "spreadsheet": {
      "command": "./scripts/local-docker-mcp.sh"
    }
  }
}

Set WORKSPACE_ROOT to override the default test directory:

WORKSPACE_ROOT=/path/to/workbooks ./scripts/local-docker-mcp.sh

This ensures you're always testing against your latest code changes without manual image rebuilds.

Behavior & Limits

• Read-only by default; write/recalc features require --recalc-enabled or the :full image
• XLSX supported for write; .xls/.xlsb are read-only
• Bounded in-memory cache honors cache_capacity
• Prefer region-scoped reads and sampling for token/latency efficiency
• screenshot_sheet requires write/recalc support and is capped to 100×30 cells per image (with split suggestions).