DuckDB UI vs H2 Database Engine

DuckDB UI is a free browser interface for a local DuckDB instance, added through the ui extension. Start it with `duckdb -ui` or `CALL start_ui()`; it opens in the default browser and is served by an HTTP server embedded in DuckDB, available by default at `http://localhost:4213`. The interface includes a SQL notebook with autocomplete and keyboard shortcuts, a catalog browser, a table explorer with column statistics, and a results viewer with sorting and filtering. The native DuckDB process gives it access to local cores, memory, and files. Queries run locally by default, and queries and data stay on the computer. Connecting to MotherDuck is optional and requires signing in. The UI is built and maintained by MotherDuck. The local server retrieves interface files from ui.duckdb.org, so alternate configured URLs should be trusted because the application can access loaded DuckDB data. The UI cannot be run directly against a read-only database and does not currently support windows_arm64.

H2 Database Engine is a free SQL database written in Java. It runs in embedded, server or mixed modes, with databases held on disk or in memory. H2 supports standard SQL and JDBC; server mode also accepts JDBC or ODBC over TCP/IP. A browser-based Console provides autocomplete. Listed database capabilities include transactions, multi-version concurrency and row-level locking, with JSON data support and high availability listed. Compatibility modes cover IBM DB2, Apache Derby, HSQLDB, MS SQL Server, MySQL, Oracle and PostgreSQL. Database files can use AES-128 encryption, while remote JDBC connections can use TLS. H2 is available for Linux, macOS and Windows, as an API, and for self-hosted or web deployment. It is dual licensed under MPL 2.0 or EPL 1.0, allowing integration into and distribution with commercial applications. The JAR is described as around 2.5 MB. The plan costs nothing.