You need a working SUMIFS or a gnarly array formula, and you need it to actually work in both Excel and Google Sheets without blowing up on edge cases. This skill walks through the full loop: it asks for your platform, separator style, sample data, then drafts formulas with named ranges and dynamic arrays where applicable. The workflow is methodical, restating your problem, explaining placement, and covering blanks, mixed types, and timezone quirks with IFERROR or LET guards. You get a worked example with 2-3 rows of input and output, plus optional troubleshooting for common mistakes. Honest take: if you've ever spent twenty minutes debugging why your VLOOKUP returns #N/A on row 847, this saves that time.
npx skills add https://github.com/composiohq/awesome-codex-skills --skill spreadsheet-formula-helper