Dry Run

A dry run is the general concept of previewing what an action would do before it actually happens, without committing anything. Nearly every tool in BalanceMCP that writes to the ledger — categorizing transactions, posting an entry, reversing one, locking a period — supports exactly this pattern.

Worth being precise about the actual mechanism rather than the informal name: the tools that write to the ledger use a parameter literally called confirm, not "dryRun." Called with confirm left at its default (false), a tool returns a preview of exactly what it would do — the accounts, the amounts, the direction — without writing anything. Called with confirm set to true, it actually performs the write. Every tool that posts, reverses, categorizes, or locks uses this same parameter name deliberately, so a model calling different tools doesn't have to guess between different conventions — the one exception is create_book, which has no confirm parameter at all and creates the book on its first call, since there's no preceding ledger state a preview could check.

A dry run genuinely reduces risk, but it isn't an ironclad guarantee that a subsequent confirm will succeed identically. The preview and the actual write run as two separate passes, not one locked transaction spanning both — something can change in the gap between them, like an account being archived, which can make a clean-looking preview fail differently once actually confirmed.

Practically, a dry run is the moment worth actually reading rather than approving reflexively, especially for a large batch — catching an obviously wrong pattern in the preview costs nothing, while catching the same mistake after confirming means reversing entries instead of simply adjusting the request.