Relay

Move data between databases, then prove nothing was lost.

Relay is a free, open-source desktop app for data migration. Connect your databases, see your infrastructure, and migrate from one database to another, same schema or not, same engine or not. Relay suggests which column goes where, runs the migration, then checks it row by row and hands you a signable report. No scripts, no YAML.

It is for anyone who has to move data: a solo developer copying production to staging, a team switching ERPs, a company moving to a new database.

What it does

1. Connect your databases (PostgreSQL, Supabase, SQL Server, MySQL, SQLite) and files (CSV, Parquet). Credentials go to the system keychain and never leave your machine.
2. See a map of your infrastructure: databases, tables, columns, volumes, links between tables.
3. Pick a source and a target, with the same schema (copy prod to staging) or a different one (a client table on PostgreSQL to a customers table on SQL Server, with renamed columns). Relay creates the tables of an empty target.
4. Validate the mappings Relay suggests. Nothing is applied until a human approves it.
5. Migrate: a dry run first, then a write in a single transaction.
6. Prove it: four families of checks (completeness, fidelity, business rules, referential integrity) give each row a verdict, Pass, Review or Fail. Decisions on gaps are remembered across runs.

Options for any migration: keep only a consistent subset of the data, and anonymize personal data, on by default from production to a non-production target.

Download

Builds for macOS (Apple silicon), Windows and Linux are published on the Releases page of this repository. The app updates itself.

The macOS build is only ad hoc signed: on first launch, macOS blocks it. Allow it in System Settings → Privacy & Security → "Open Anyway".

Build from source

Requirements: Bun and uv (the engine runs on Python 3.14; uv installs it).

bun install                      # once, from the repository root
bun run desktop                  # run the desktop app

cd engine
uv sync --all-extras             # engine and database drivers
uv run pytest && uv run ruff check . && uv run ty check

The engine needs neither Java nor Spark. See engine/README.md for the engine and its developer CLI, and apps/desktop/README.md for the app and packaging.

Repository layout

Path	Content
engine/	The engine (Python, Polars): read, transform, write, verify; plus a developer CLI
apps/desktop/	The desktop app (Electron, Next.js), the main interface
apps/web/	The web app, later
apps/landing/	The landing page
packages/ui/	@relay/ui, the shared design system (shadcn/ui, Tailwind CSS)
packages/contract/	The results schema shared by the engine and the apps
supabase/	Database schema for optional team accounts
relay-brand/	Logos
docs/	Technical documentation

Documentation

• Architecture
• Mapping specification
• Results model
• Source catalog, for the CLI
• Performance at scale
• Roadmap

Contributions are welcome: see CONTRIBUTING.md.

License

Apache License 2.0. Copyright 2026 Bastien Cochet.