excel-spreadsheets

name	excel-spreadsheets
description	Use when generating or validating professional Excel workbooks, formulas, imports, charts, formatting, macros, or spreadsheet deliverables.
metadata	{"portable":true,"compatible_with":["claude-code","codex"]}

Excel Spreadsheets Skill

Acknowledgement: Shared by Peter Bamuhigire, techguypeter.com, [phone].

Required Inputs

Input	Required	Use
Decision, audience, and deliverable	yes	Bound the business outcome
Source evidence, constraints, and owner	yes	Ground recommendations and accountability
Approved budget, customer data, or production artefacts	conditional	Support high-impact execution

Capability and permission contract

Default to read-only analysis and drafting. Do not publish, send, price, promise, alter customer records, commit budget, or modify production artefacts without explicit authority and a named approver. Minimise confidential data, preserve provenance, and keep reversible copies.

Degraded mode

If evidence, stakeholder decisions, specialist tooling, or authoritative commercial data are unavailable, deliver a labelled draft, checklist, or decision memo. State what was not verified and do not claim approval, publication, financial accuracy, or customer acceptance.

Decision rules

Condition	Action	Stop condition
Output creates a commercial, customer, or delivery commitment	Obtain named approval before release	Authority or terms are unclear
Evidence supports a reversible draft	Produce it with assumptions and owner	Required evidence conflicts
Tooling or data is incomplete	Specify validation	A final executable artefact is expected

Domain Anti-Patterns

• Inventing customer evidence, prices, benchmarks, or approvals. Fix: cite the source or mark the gap.
• Publishing or sending a draft without authority. Fix: retain draft status and name the approver.
• Hiding assumptions inside polished prose. Fix: expose them beside each affected decision.
• Polishing presentation while the decision remains unclear. Fix: resolve audience, owner, and acceptance criteria.
• Treating unavailable tooling as passed validation. Fix: record the unassessed check.

Use When

• Generate world-class, professionally designed Microsoft Excel spreadsheets and handle all Excel/spreadsheet workflows. Use when: generating .xlsx files from apps or scripts (openpyxl, xlsxwriter, PhpSpreadsheet, pandas), importing or parsing...

Evidence Produced

Category	Artifact	Format	Example
Release evidence	Generated Excel workbook	Branded .xlsx artefact compliant with the excel-spreadsheets design standard	docs/output/dashboard-2026-04-16.xlsx

References

• Use the references/ directory for deep detail after reading the core workflow below.

Excel done right looks like a financial analyst and a graphic designer collaborated on it. Done wrong, it's a wall of unformatted data nobody trusts. This skill covers both the code that generates Excel files and the design standards that make them world-class.

Reference files (read when needed):

• references/design-standards.md — layout, colour palettes, typography, table structure, conditional formatting, print setup
• references/formulas-functions.md — XLOOKUP, dynamic arrays, LET, LAMBDA, SUMIFS, MAXIFS/MINIFS, essential formula patterns
• references/programmatic-generation.md — openpyxl, xlsxwriter, PhpSpreadsheet, pandas — code patterns for generating professional Excel from apps
• references/charts-pivot.md — chart types, professional chart formatting, PivotTables, slicers, dashboards
• references/financial-modeling.md — PMT, PV, FV, NPV, IRR; Goal Seek, Data Tables, Scenario Manager, Solver; modeling golden rules; formula debugging
• references/finance-accounting-workbooks.md — bookkeeping ledgers, trial balance, AR/AP aging, bank reconciliation, fixed assets, budgets, cost accounting, statement checks, and finance dashboards
• references/python-automation.md — Excel–Python–Excel workflow, advanced read_excel(), 6-step export, pivot_table/merge/crosstab, email automation, =PY() function, xlwings
• references/vba-macros.md — recording/running macros, VBA golden rules, common patterns, keyboard shortcuts reference
• references/quality-checklist.md — pre-delivery checklist

Sources: Microsoft Excel 365 Bible (Walkenbach/Alexander); Microsoft Excel Bible 2026; Ultimate Excel Formula & Function Reference Guide; Excel 2025 All-in-One; Excel 2019 Advanced Topics (George); Advanced Excel for Productivity (Urban); Automate Excel with Python (Wengler, 2026); Python in Excel Advanced (Van Der Post)

---

The Standard

Every spreadsheet produced must pass: a data analyst and a designer would both be satisfied. Specifically:

1. Data lives in a properly structured Excel Table — never raw ranges
2. Every number has an intentional format (currency, %, dates — never General)
3. Visual hierarchy is clear: header rows are distinct, data rows are readable
4. Formulas are correct, efficient, and use structured references where possible
5. The file opens correctly on any machine, in any regional locale

---

Core Architecture Rules

Rule 1 — Always use Excel Tables

Convert every data range to an Excel Table (Ctrl+T) immediately. Tables give you:

• Structured references: =Table1[Amount] instead of =$C$2:$C$100
• Auto-expansion when new rows are added
• Built-in filter arrows
• Automatic banded rows
• Named reference for programmatic access

Programmatic: In openpyxl, xlsxwriter, and PhpSpreadsheet, always add a Table (ListObject) definition over data ranges. See references/programmatic-generation.md.

Rule 2 — One table per sheet, one topic per sheet

Never mix multiple unrelated datasets on one sheet. Use separate sheets with clear names. Sheet names: PascalCase or Title Case, max 20 characters, no spaces (use underscores if needed).

Rule 3 — Separate data from presentation

• Data sheets — raw data in Tables, no decorative formatting, no merged cells
• Report/Dashboard sheets — formulas pulling from data sheets, full formatting treatment
• Configuration sheets (hidden) — lookup lists, parameters, constants

Rule 4 — Never merge cells in data ranges

Merged cells break sorting, filtering, PivotTables, and programmatic reading. For visual centering of headers, use Center Across Selection instead (Format Cells → Alignment → Horizontal: Center Across Selection).

---

Excel Table Design

Read references/design-standards.md for full colour palettes and formatting specs.

Standard table anatomy:

Row 1:  Sheet title / document header   ← merged+centred, large font, brand colour
Row 2:  Subtitle / date / filter info   ← smaller, grey
Row 3:  [blank spacer row]
Row 4:  Table header row                ← Excel Table header (bold, brand fill, white text)
Row 5+: Data rows                       ← banded, 11pt, left/right aligned by type
Last:   Totals row                      ← bold, top border, SUM/AVERAGE via Table totals row

Column alignment rules:

• Text columns → left-aligned
• Number/currency columns → right-aligned
• Date columns → right-aligned or centred
• Status/category columns → centred
• Header row → match column alignment (not always centred)

---

Number Formats (critical — never leave as General)

Data type	Format code	Example output
Currency (UGX/KES/TZS)	#,##0	1,250,000
Currency with decimals	#,##0.00	1,250,000.00
USD	"$"#,##0.00	$1,250.00
Percentage	0.00%	12.50%
Percentage (whole)	0%	13%
Date (display)	DD MMM YYYY	05 Apr 2026
Date (ISO sort)	YYYY-MM-DD	2026-04-05
Large numbers	#,##0.0,,"M"	1.3M
Negative red	#,##0.00;[Red]-#,##0.00	-500.00 (red)
Integer	#,##0	42,000
Duration (hours)	[h]:mm	37:30

Custom format anatomy: positive;negative;zero;text

---

Essential Formulas

Read references/formulas-functions.md for full formula patterns. Core rules:

Use structured references in Tables:

=SUMIFS(Sales[Amount], Sales[Region], [@Region], Sales[Status], "Paid")

XLOOKUP over VLOOKUP always:

=XLOOKUP([@ID], Products[ID], Products[Price], "Not found", 0)

Dynamic arrays for reports:

=FILTER(Sales[#All], (Sales[Region]="East")*(Sales[Month]=B2))
=SORT(UNIQUE(Sales[Category]))
=SEQUENCE(12, 1, DATE(2026,1,1), 30)

The last example generates dates 30 days apart, not calendar-month dates. For monthly schedules, use a calendar-aware formula and verify February, month-end and year-boundary results in the target spreadsheet application.

LET for complex formulas (readability + performance):

=LET(
  data, FILTER(Sales[Amount], Sales[Status]="Paid"),
  avg, AVERAGE(data),
  IF(avg>100000, "Above target", "Below target")
)

---

Data Validation

Every user-input column must have data validation. Never let free-form text corrupt a data column.

Dropdown from a Table column:

• Source: =INDIRECT("Table1[Category]") or a named range
• Input message: "Select a category from the list"
• Error alert: Stop — "Invalid entry. Please select from the list."

Date range validation:

• Allow: Date, Between, =TODAY()-365, =TODAY()+365

Whole number range:

• Allow: Whole number, Between, 0, 1000000

---

Conditional Formatting

Apply to entire Table columns, not fixed ranges (so it auto-expands with the Table).

Standard patterns:

• Heat map (numeric): 3-colour scale, low=white, mid=yellow, high=brand colour
• Above/below average: Green fill for above, red fill for below
• Status column: Formula-based — =[@Status]="Paid" → green; =[@Status]="Overdue" → red
• Data bars: For ranking/comparison columns — no border, solid fill, brand colour
• Duplicate detection: =COUNTIF(Table1[Email],[@Email])>1 → orange fill

---

Professional Finishing

Read references/design-standards.md → Professional Finishing section.

Freeze panes: Always freeze the header row (and optionally the first column for wide tables). View → Freeze Panes → Freeze Top Row.

Print setup (every sheet intended for printing):

• Page Layout → Page Setup:
  • Orientation: Landscape for wide tables
  • Scale to fit: 1 page wide, auto tall
  • Print titles: Row 1 (and Table header row) to repeat on every page
  • Margins: Narrow (0.64 cm) for data tables; Normal for reports
  • Header: Document name left, date centre, page number right
  • Footer: "Page &P of &N" centred, confidential notice if needed

Workbook hygiene:

• Delete all unused sheets (Sheet1, Sheet2, Sheet3)
• Name every sheet clearly
• Set the first sheet as the active sheet on open
• Remove all #REF!, #VALUE!, #NAME? errors before delivery

---

Programmatic Generation

Read references/programmatic-generation.md for full code patterns per language/library.

Library selection:

Use case	Library	Language
Full formatting + charts	openpyxl	Python
Large data, max performance	xlsxwriter	Python
PHP apps	PhpSpreadsheet	PHP
Data analysis output	pandas + openpyxl	Python
Node.js apps	exceljs	JavaScript

Non-negotiable programmatic rules:

1. Always define a Table (add_table / addTableStyleInfo) over data — never just write raw rows
2. Always set column widths — auto-width from content, with min 8 and max 60 characters
3. Always apply number formats to numeric columns — never leave as default
4. Always freeze the header row
5. Always set a tab colour per sheet for multi-sheet workbooks
6. Always use a professional table style (TableStyleMedium2 or equivalent)

---

Import / Parsing Patterns

When reading Excel files in applications:

Always:

• Read with header=0 (first row is headers) unless the file has multi-row headers
• Strip whitespace from string columns after reading
• Validate expected columns exist before processing — fail early with clear error messages
• Parse date columns explicitly (don't rely on auto-detection)
• Handle merged header cells by forward-filling merged values

Never:

• Assume column order — always reference by column name, not index
• Assume data starts at row 1 — check for title rows above the table
• Trust data types — validate and coerce explicitly

Python pattern:

import pandas as pd

df = pd.read_excel("file.xlsx", sheet_name="Sales", header=0)
df.columns = df.columns.str.strip()  # remove whitespace from headers
df["Date"] = pd.to_datetime(df["Date"], dayfirst=True)
df["Amount"] = pd.to_numeric(df["Amount"], errors="coerce")
df = df.dropna(subset=["ID"])  # drop rows with no ID

---

Financial Functions Quick Reference

Read references/financial-modeling.md for full formulas, examples, and What-If tools. Read references/finance-accounting-workbooks.md when the workbook is a ledger, trial balance, aging report, reconciliation, financial model, budget, forecast, cost model, or finance dashboard.

Function	Use case	Key rule
=PMT(rate, nper, pv)	Monthly loan/mortgage payment	Rate and nper must match time unit (÷12 for monthly)
=PV(rate, nper, pmt)	Present value of an annuity	Cash inflows = positive, outflows = negative
=FV(rate, nper, pmt)	Future value of savings/investment	pmt is negative (cash going out)
=NPV(rate, cashflows)	Net present value	Add period-0 investment separately outside NPV()
=IRR(cashflows)	Internal rate of return	First value should be negative (initial outlay)

What-If tools:

• Goal Seek — find the input that achieves a target output (Data → What-If Analysis → Goal Seek)
• Scenario Manager — store and compare named sets of input values (Base/Optimistic/Pessimistic)
• Data Tables — calculate output across a range of input values (1-variable or 2-variable)
• Solver — optimise across multiple variables with constraints (requires Solver add-in)

---

VBA Macros

Read references/vba-macros.md for full VBA patterns and keyboard shortcuts.

Record a macro: View → Macros → Record Macro (or status bar button bottom-left) Run a macro: Alt+F8 or assigned shortcut key Edit a macro: Alt+F11 opens the VBA editor

Critical shortcuts:

• Ctrl+Arrow — jump to end of data range
• F2 — edit mode with colour-coded cell references
• F4 — toggle $A$1 → A$1 → $A1 → A1 (absolute/relative)
• Ctrl+Shift+Enter — legacy array formula (prefer dynamic arrays)
• Alt+H+O+I — auto-fit column width

---

Customisation Quick Reference

What to change	Where
Table colour palette	references/design-standards.md → Colour Palettes
Formula patterns	references/formulas-functions.md
openpyxl/xlsxwriter code	references/programmatic-generation.md
Chart types and formatting	references/charts-pivot.md
Financial functions & What-If	references/financial-modeling.md
Finance/accounting workbooks	references/finance-accounting-workbooks.md
Python automation & =PY()	references/python-automation.md
VBA macros & keyboard shortcuts	references/vba-macros.md
Pre-delivery checks	references/quality-checklist.md

Quality Standards

Workbook acceptance requires formula, source, error-state, protection, accessibility, and rendered-layout checks at the intended application boundary.

Outputs

Artefact	Consumer	Acceptance condition
Validated workbook and QA note	Analyst or operational owner	Formulas recalculate, source ranges are traceable, error states are handled, and visual checks cover the intended spreadsheet application