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Writing a brief Cowork can execute, then reading its plan before it starts

A good brief names a result, its source, its destination and the workspace concerned, as if for a colleague starting that same day; Cowork answers with a plan that needs reading, because a wrong assumption spotted before execution is corrected at no cost, spotted after it can mean undoing writes already made.

Cowork works on a simple principle: you describe a wanted result, then come back later to review finished work. This principle only holds if the initial brief says enough for a finished piece of work to have a checkable meaning.

The four elements of a usable brief

A brief that works names four things, exactly as you would to a colleague starting on the subject that same day. The expected result, a file, a report, a tidied folder. The source, where the starting material sits, which folder, which files. The destination, where the result should land, a new file, an existing folder, an overwrite in place. The workspace concerned, the Cowork project all of this should happen in, so that the memory and attached folders are the right ones. These four elements are not a form imposed by Anthropic, they are a method: leaving one out lets Cowork guess in its place, and guessing a folder or a format that is not the one expected costs more to fix than one extra sentence written into the initial brief.

Weak brief: "Sort out the invoices."
Usable brief: "Read the PDF invoices in the Invoices_2026 folder, create a summary table in a new Recap_2026.xlsx file, one row per invoice, in this same project."

The plan, your last chance before writing

Faced with a brief, Cowork does not get straight to work: it first proposes a plan, a sequence of steps it intends to follow. Reading this plan before letting it start changes the nature of the error that can occur. A wrong assumption spotted in the plan, the wrong folder targeted, a destination file that would overwrite an existing one, is fixed by changing a sentence in the brief, at no cost whatsoever. The same wrong assumption spotted after execution can mean undoing writes already made, digging up an old version of an overwritten file, or sorting out what changed across an entire folder.

The same review reflex applies to the approval level chosen for the task, detailed in the next lesson: a plan read carefully in manual mode beats a plan skimmed in automatic mode.