excel-mcp | SkillBundle

Excel MCP Server Skill

Provides 326 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(action: 'create', table_name: 'SalesData', range_address: 'A1:D100')

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

Rule 5: Session Lifecycle

Pass that same value as session_id on every session-based follow-up call. sessionId above is a local variable, not an MCP argument name. When reusing a session from file(list), copy the matching entry's sessionId value into session_id. Never guess or substitute a session.

Unclosed sessions leave Excel processes running, locking files.

Rule 6: Data Model Prerequisites

DAX operations require tables in the Data Model:

Rule 7: Power Query Development Lifecycle

BEST PRACTICE: Test-First Workflow

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:

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: