Quick Reference: File Management, Data Processing & Output

• Folder access: Granted per session, scoped to the selected folder and its subfolders only
• Read/write: Free within the granted folder — no permission prompt
• Deletion: Requires explicit user approval via system-level prompt
• Overwrites: No permission prompt — an overwritten file is just as lost as a deleted one
• Path traversal: Impossible — Claude cannot access parent directories even if you type the full path
• Session boundaries: Each new session requires re-selecting a working folder

The #1 security rule: Never point Cowork at Documents, Desktop, or your home folder. Always create a dedicated workspace and copy only the files you need.

Common trap: Analysing files one at a time in separate sessions loses cross-document synthesis. Keep all related files in the same working folder.

What Cowork can create:

• Excel (.xlsx) with working formulas (VLOOKUP, SUMIFS, IF), conditional formatting, charts, and multiple tabs
• Word (.docx) with heading hierarchies, tables, bullet lists, and page breaks
• PowerPoint (.pptx) with structured slides, data tables, and logical flow
• PDF reports with professional formatting

What it cannot do well:

• Corporate-branded slide decks (no custom themes or animations — treat as a first draft)
• Designer-quality visual layouts

Quality depends on prompt specificity:

• Trigger phrases for parallelism: "for each one," "analyse all," "process every," "in parallel"
• Best for: Renaming, converting, extracting, summarising many files
• Sub-agents handle: Independent units of work (one file per agent)
• Main agent handles: Combining results after all sub-agents complete
• Always review the plan — errors multiply across all files simultaneously

Sequential vs Parallel decision rule:

• Files are independent (each can be processed alone) → Parallel
• Step 2 needs Step 1's output (e.g., rename based on content analysis) → Sequential

For every document creation task, specify:

• File type — .xlsx, .docx, .pptx, .pdf, .csv
• File name — e.g., "Q1-Regional-Summary.xlsx"
• Structure — tabs, sections, slides, pages
• Formulas — SUMIFS, VLOOKUP, IF, SUBTOTAL
• Formatting — conditional highlighting, colour coding rules
• Charts — bar, pie, line; what data they visualise
• Column names — explicit headers for each data column
• Naming conventions — for batch-produced files

Without a format specification, Claude defaults to a conversational text response in the chat window rather than creating a file on your system.