Spreadsheet Read MCP

Read-only MCP server for spreadsheet analysis. 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 (via umya-spreadsheet)
• 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 runs once and caches bounds for sheet_overview, find_value, read_table, table_profile

Tool Surface

Hidden/optional: sheet_styles, sheet_statistics, scan_volatiles, get_manifest_stub, close_workbook.

Example

Request: Profile a detected region

{
  "tool": "table_profile",
  "arguments": {
    "workbook_id": "budget-2024-a1b2c3",
    "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)

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

For stdio mode (e.g., Claude Code):

docker run -i --rm -v /path/to/workbooks:/data ghcr.io/psu3d0/spreadsheet-read-mcp:latest \
  --transport stdio

Cargo Install

cargo install spreadsheet-read-mcp
spreadsheet-read-mcp --workspace-root /path/to/workbooks

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.

Local Development Testing

To test local changes without rebuilding Docker, point your MCP client directly at the cargo build:

Claude Code (Local Build)

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

{
  "mcpServers": {
    "spreadsheet": {
      "command": "cargo",
      "args": ["run", "--release", "--manifest-path", "/path/to/spreadsheet-read-mcp/Cargo.toml", "--", "--workspace-root", "/path/to/workbooks", "--transport", "stdio"]
    }
  }
}

Or build once and run the binary directly:

cargo build --release

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

Cursor / VS Code (Local Build)

In .vscode/settings.json or user settings:

{
  "mcp.servers": {
    "spreadsheet": {
      "command": "cargo",
      "args": ["run", "--release", "--manifest-path", "/path/to/spreadsheet-read-mcp/Cargo.toml", "--", "--workspace-root", "${workspaceFolder}", "--transport", "stdio"]
    }
  }
}

Tip: Use cargo build --release first, then point to the binary for faster startup.

MCP Client Configuration

Claude Desktop (Docker)

Add to claude_desktop_config.json:

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

Claude Desktop (Binary)

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

Cursor / VS Code (Docker)

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

Cursor / VS Code (Binary)

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

HTTP Mode

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

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

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 caching — Detection runs once per sheet; region_id lookups are O(1)
• Sampling modes — distributed sampling reads evenly across rows without loading everything
• 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.

Behavior & Limits

• Strictly read-only; no mutation, recalc, or VBA execution
• XLSX parsed fully; .xls/.xlsb discovered but not parsed
• Bounded in-memory cache honors cache_capacity
• Prefer region-scoped reads and sampling for token/latency efficiency