Excel MCP Server Skill Skill

Excel MCP Server Skill

Provides 325 Excel operations via Model Context Protocol. The MCP Server hosts the ExcelMCP Service in-process and calls it directly for low-latency Excel automation. 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 |

Write format codes in US notation (, grouping, . decimal) regardless of the machine's locale — Excel translates them. The rendered separators follow the user's Windows regional settings, so $#,##0.00 shows $1.234,56 on a German system. Don't "fix" that by swapping the separators in the format code; it would break on every other locale.

Workflow:

1. range set-values (data is now in cells)
2. range set-number-format (apply format)
3. range_format auto-fit-columns (formatted values are wider than raw ones)

Step 3 is not optional. A column sized for 45678 is too narrow once that value renders as 2025-01-22 or $1,234.56, and Excel displays ##### instead of the number.

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')"]
}

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 | | Run what-if analysis | analysis | goal-seek, create-scenario, create-data-table | | 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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