Godwit Sync is a command-line tool for migrating and continuously syncing data between S3-compatible object stores and local filesystems, in three directions: filesystem-to-S3, S3-to-filesystem, and S3-to-S3. Before any transfer it builds an editable SQLite plan listing the exact objects and byte counts that will move; run it with --plan-only to inspect or edit the plan first. Incremental runs move only objects whose size, ETag, or mtime changed since the last completed run. A killed run re-plans pending and failed objects instead of skipping them. Every run is verifiable: real per-object MD5 checksums (not just ETags), on-demand checksum verification with plan verify, a status REST endpoint, Prometheus metrics, and automation-friendly exit codes for cron and CI. Transfers are parallel with multipart uploads and partial-upload recovery, resumable from the exact checkpoint after a crash, rate-limited on reads and writes, and true stream-to-stream (object data is never staged or cached on local disk). Migrations are version-aware, moving every object version rather than only the latest, and object metadata and tags are preserved exactly as stored at the source. Godwit Sync works with any S3-compatible endpoint on both sides, including AWS S3, MinIO, Cloudflare R2, Backblaze B2, Wasabi, and DigitalOcean Spaces, plus self-hosted storage such as RustFS, Garage, SeaweedFS, versitygw, and QNAP QuObjects. It is compatible with immutable Object Lock (WORM) target buckets. The license is validated locally and offline, and data moves directly between source and destination without passing through Godwit Sync servers. Available for Linux, macOS, Windows, and FreeBSD, plus official Docker images.