Limitations
What's genuinely different by tier, and a few honest gaps worth knowing about up front.
Free resolves only direct (single-hop) trigger/procedure/view/function references — a procedure that calls another procedure needs Standard or Multi to be fully resolved and materialized.
Building test databases from more than one data source at the same time is a Multi-tier feature.
Unlike 00DB (and unlike this tool's own predecessor), SQL Simulator's Docker sandboxes have no idle or max-lifetime self-destruct. A sandbox you build keeps running — and keeps using your container's resources — until you tear it down yourself with Destroy Image, or with your own Docker tooling.
Each sandbox container has one fixed login and one fixed database per engine. Running Preview Image (or Postview Image, or Dry Run) for two data sources that resolve to the same sandbox target at the same time will fail with a clear per-data-source error rather than silently corrupting anything — give each its own Sandbox target (see Technical Overview) if you need them to run concurrently.
SQL Server and Oracle discover object dependencies through each engine's own relational catalogs; PostgreSQL and MySQL rely more on scanning function/procedure body text for some cases. In practice this rarely changes what gets pulled in, but it's worth knowing if a dependency chain in Postgres or MySQL doesn't resolve the way you expect.