Write hand-authored SQL migrations for data seeding or DDL that `drizzle-kit generate` doesn't support, and validate migration-history consistency with `drizzle-kit check`/`up`.

Documented steps

1. Run `npx drizzle-kit generate --custom --name=<name>` (e.g. `npx drizzle-kit generate --custom --name=seed-users`) to create an empty migration folder `drizzle/<timestamp>_<name>/` with a blank `migration.sql` — no schema diffing occurs for a custom migration.
2. Manually edit the generated `migration.sql` with your own SQL, e.g. seed data: `INSERT INTO "users" ("name") VALUES('Dan'); INSERT INTO "users" ("name") VALUES('Andrew');` or DDL not yet supported by Drizzle Kit.
3. Apply it like any normal migration: `npx drizzle-kit migrate` (or the programmatic `migrate(db)` call from `drizzle-orm/<driver>/migrator`).
4. Per the current docs, only raw `.sql` custom migrations are supported — JavaScript/TypeScript migration or seeding scripts are not yet supported (tracked in GitHub discussion #2832 at the time of writing).
5. Run `npx drizzle-kit check` (requires only `dialect`, e.g. `npx drizzle-kit check --dialect=postgresql`) to detect race conditions/collisions in the generated migration history — most useful in CI and when multiple developers alter the schema on separate branches.
6. If Drizzle Kit ships a breaking change to its internal snapshot JSON format, run `npx drizzle-kit up --dialect=<dialect>` to upgrade existing snapshot files in the `out` folder to the new version.
7. Reference: https://orm.drizzle.team/docs/kit-custom-migrations https://orm.drizzle.team/docs/drizzle-kit-generate https://orm.drizzle.team/docs/drizzle-kit-check https://orm.drizzle.team/docs/drizzle-kit-up