pgmagmig

pgmagmig is a PostgreSQL migration tool with an integrated schema differ, powered by PGlite (PostgreSQL compiled to WASM).

Schema extraction, DDL generation, diffing, and diff validation all run in-process against PGlite. No external PostgreSQL server is required for any of these operations. A real PostgreSQL server is only needed when actually applying migrations to a database.

What pgmagmig does

• Extracts a database schema into a JSON representation by querying PostgreSQL system catalogs.
• Generates DDL from a schema, producing readable CREATE TABLE statements with defaults, constraints, and foreign keys inlined.
• Diffs two schemas and produces the DDL to transform one into the other, with structured hazard annotations on destructive or lock-heavy statements.
• Validates every generated diff by applying it to an in-process PGlite instance and comparing the result to the expected schema.
• Drafts migration files in YAML format, with up and down SQL, automatically validated in both directions.
• Runs migrations against a real PostgreSQL database, with per-migration transactions, branch switching, and rollback support.
• Exposes an ephemeral PGlite via Unix socket or TCP, so any tool that speaks PostgreSQL (Prisma, sqlc, pgtyped, psql) can work against your migration-defined schema without a running database server.

Why PGlite?

PGlite is real PostgreSQL 17 compiled to WASM. It’s not an approximation or a compatibility layer. The system catalogs, type system, DDL parsing, and expression evaluation are identical to a full PostgreSQL server. This means pgmagmig’s schema extraction and diff validation are tested against the same engine your production database runs.

The practical benefit: you can extract, diff, and validate schemas on your laptop, in CI, or anywhere Node.js runs, without provisioning a PostgreSQL instance.