mmk dry-run

Shows what mmk up or mmk down would do, without doing it.

npx mmk dry-run <up|down> [file] [options]

Examples

npx mmk dry-run up                # what would mmk up run?
npx mmk dry-run up <file>         # would this file run?
npx mmk dry-run down              # what would mmk down undo?
npx mmk dry-run down --steps 2    # what would the last two be?

What it does

It works out the same list of files the real command would, prints it, and stops. It reads the history, but never writes and never takes the lock, so it's safe against production even while a deploy is running.

$ npx mmk dry-run up
Loaded config from mmk.config.js
◎ Dry-run  Would apply: 3
┌─────────────────────────────────────────────┬─────────┬───────┬────────────┬──────────┬────────┐
│ Migration                                   │ Status  │ Batch │ Applied At │ Checksum │ Author │
├─────────────────────────────────────────────┼─────────┼───────┼────────────┼──────────┼────────┤
│ 20261012090000-add-users-email-index.js     │ pending │       │            │ —        │        │
├─────────────────────────────────────────────┼─────────┼───────┼────────────┼──────────┼────────┤
│ 20261012091500-backfill-order-status.js     │ pending │       │            │ —        │        │
├─────────────────────────────────────────────┼─────────┼───────┼────────────┼──────────┼────────┤
│ 20261014103000-add-orders-customer-index.js │ pending │       │            │ —        │        │
└─────────────────────────────────────────────┴─────────┴───────┴────────────┴──────────┴────────┘

$ npx mmk dry-run down --steps 2
◎ Dry-run  Would revert: 2
┌─────────────────────────────────────────────┬─────────┬───────┬─────────────────────┬──────────┬──────────┐
│ Migration                                   │ Status  │ Batch │ Applied At          │ Checksum │ Author   │
├─────────────────────────────────────────────┼─────────┼───────┼─────────────────────┼──────────┼──────────┤
│ 20261014103000-add-orders-customer-index.js │ applied │ 3     │ 2026-10-15 22:47:26 │ ok       │ Asha Rao │
├─────────────────────────────────────────────┼─────────┼───────┼─────────────────────┼──────────┼──────────┤
│ 20261012091500-backfill-order-status.js     │ applied │ 2     │ 2026-10-15 22:47:26 │ ok       │ Asha Rao │
└─────────────────────────────────────────────┴─────────┴───────┴─────────────────────┴──────────┴──────────┘

For down, the rows are in the order they'd be undone.

Because it predicts the real command, it also fails when the real command would. For example, with a namespace whose older records haven't been adopted yet, it refuses with NAMESPACE_UNADOPTED instead of listing applied migrations as pending.

Options

Option	What it does
up or down	Required. Which command to preview.
[file]	Preview just this file.
--steps <n>	With down: preview undoing the last n files.
--json	Print the rows as JSON.

The global flags work here too.

Make it a habit

Put npx mmk dry-run up right before npx mmk up in your deploy job. It costs a second, and the job log then shows exactly what was about to run.