Format on Save

BMO can format files immediately after agent file mutations write bytes to the workspace. The formatter runs before workspace history and read snapshots are recorded, so the next edit sees the same bytes that are on disk.

Format on save is opt-in:

[options.format_on_save]
enabled = true
fail_on_error = false

[[options.format_on_save.rules]]
id = "go"
extensions = [".go"]
command = "gofumpt -w {{path}}"
timeout_seconds = 30

Rules match by file extension, case-insensitively, and the first matching rule wins. Command templates support {{path}} for the absolute file path and {{cwd}} for the workspace directory. The built-in Go rule tries gofumpt -w and falls back to gofmt -w when gofumpt is unavailable.

The default is fail-open. If a formatter is missing, times out, or exits non-zero, the file mutation still succeeds and BMO records a bounded metadata event. Set fail_on_error = true for repositories that prefer failed writes over unformatted content.

These save points run formatters: write, edit, multiedit, semantic LSP symbol edits, and staged_accept / staged_accept_all. apply_patch proposals format when accepted, not while they are only staged.

Inspect the detached configuration posture with:

bmo config show-format-on-save --format=json