Excel MCP Server Skill Skill

Excel MCP Server Skill

Provides 225 Excel operations via Model Context Protocol. The MCP Server forwards all requests to the shared ExcelMCP Service, enabling session sharing with CLI. Tools are auto-discovered - this documents quirks, workflows, and gotchas.

Workflow Checklist

| Step | Tool | Action | When | |------|------|--------|------| | 1. Open file | file | open or create | Always first | | 2. Create sheets | worksheet | create, rename | If needed | | 3. Write data | range | set-values | Always (2D arrays) | | 4. Format | range | set-number-format | After writing | | 5. Structure | table | create | Convert data to tables | | 6. Save & close | file | close with save: true | Always last |

Preconditions

Windows host with Microsoft Excel installed (2016+)
Use full Windows paths: C:\Users\Name\Documents\Report.xlsx
Excel files must not be open in another Excel instance

Calculation Mode Workflow (Batch Performance)

Use calculation_mode for bulk write performance optimization. When writing many values or formulas, disable auto-recalc to avoid recalculating after every cell:

1. calculation_mode(action: 'set-mode', mode: 'manual')  → Disable auto-recalc
2. Perform all writes (range set-values, set-formulas)
3. calculation_mode(action: 'calculate', scope: 'workbook')  → Recalculate once
4. calculation_mode(action: 'set-mode', mode: 'automatic')  → Restore default

Note: You do NOT need manual mode to read formulas - range get-formulas returns formula text regardless of calculation mode.

CRITICAL: Execution Rules (MUST FOLLOW)

Rule 1: NEVER Ask Clarifying Questions

STOP. If you're about to ask "Which file?", "What table?", "Where should I put this?" - DON'T.

| Bad (Asking) | Good (Discovering) | |--------------|-------------------| | "Which Excel file should I use?" | file(list) → use the open session | | "What's the table name?" | table(list) → discover tables | | "Which sheet has the data?" | worksheet(list) → check all sheets | | "Should I create a PivotTable?" | YES - create it on a new sheet |

You have tools to answer your own questions. USE THEM.

Rule 2: Always End With a Text Summary

NEVER end your turn with only a tool call. After completing all operations, always provide a brief text message confirming what was done. Silent tool-call-only responses are incomplete.

Rule 3: Format Data Professionally

Always apply number formats after setting values:

| Data Type | Format Code | Result | |-----------|-------------|--------| | USD | $#,##0.00 | $1,234.56 | | EUR | €#,##0.00 | €1,234.56 | | Percent | 0.00% | 15.00% | | Date (ISO) | yyyy-mm-dd | 2025-01-22 |

Workflow:

1. range set-values (data is now in cells)
2. range set-number-format (apply format)

Rule 4: Use Excel Tables (Not Plain Ranges)

Always convert tabular data to Excel Tables:

1. range set-values (write data including headers)
2. table create tableName="SalesData" rangeAddress="A1:D100"

Why: Structured references, auto-expand, required for Data Model/DAX.

Rule 5: Session Lifecycle

1. file(action: 'open', path: '...')  → sessionId
2. All operations use sessionId
3. file(action: 'close', save: true)  → saves and closes

Unclosed sessions leave Excel processes running, locking files.

Rule 6: Data Model Prerequisites

DAX operations require tables in the Data Model:

Step 1: Create table → Table exists
Step 2: table(action: 'add-to-datamodel') → Table in Data Model
Step 3: datamodel(action: 'create-measure') → NOW this works

Rule 7: Power Query Development Lifecycle

BEST PRACTICE: Test-First Workflow

1. powerquery(action: 'evaluate', mCode: '...') → Test WITHOUT persisting
2. powerquery(action: 'create', ...) → Store validated query
3. powerquery(action: 'refresh', ...) → Load data

Why evaluate first:

Catches syntax errors and missing sources BEFORE creating permanent queries
Better error messages than COM exceptions from create/update
See actual data preview (columns + sample rows)
No cleanup needed - like a REPL for M code
Skip only for trivial literal tables

Common mistake: Creating/updating without evaluate → pollutes workbook with broken queries

Rule 8: Targeted Updates Over Delete-Rebuild

Prefer: set-values on specific range (e.g., A5:C5 for row 5)
Avoid: Deleting and recreating entire structures

Why: Preserves formatting, formulas, and references.

Rule 9: Follow suggestedNextActions

Error responses include actionable hints:

{
  "success": false,
  "errorMessage": "Table 'Sales' not found in Data Model",
  "suggestedNextActions": ["table(action: 'add-to-data-model', tableName: 'Sales')"]
}

Rule 10: Use Calculation Mode for Bulk Write Performance

When writing many values/formulas (10+ cells), use calculation_mode to avoid recalculating after every write:

1. calculation_mode(action: 'set-mode', mode: 'manual')  → Disable auto-recalc
2. Perform data writes (range set-values, set-formulas)
3. calculation_mode(action: 'calculate', scope: 'workbook')  → Recalculate once at end
4. calculation_mode(action: 'set-mode', mode: 'automatic')  → Restore default

When NOT needed: Reading formulas, small edits (1-10 cells), or when you need immediate calculation results.

Tool Selection Quick Reference

| Task | Tool | Key Action | |------|------|------------| | Create/open/save workbooks | file | open, create, close | | Write/read cell data | range | set-values, get-values | | Format cells | range | set-number-format | | Create tables from data | table | create | | Add table to Power Pivot | table | add-to-data-model | | Create DAX formulas | datamodel | create-measure | | Create PivotTables | pivottable | create, create-from-datamodel | | Filter with slicers | slicer | set-slicer-selection | | Create charts | chart | create-from-range | | Control calculation mode | calculation_mode | get-mode, set-mode, calculate | | Visual verification | screenshot | capture, capture-sheet |

Reference Documentation

See references/ for detailed guidance:

Agent Skills: Excel MCP Server Skill

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