Run one read-only query on an app's database

Runs one SELECT on the app's own database and returns at most 50 rows, to see what is in it while building or debugging. It only reads: anything that writes or changes the schema is refused, and the query runs as a subquery with the row limit outside it. Email addresses and phone numbers in the result are masked, long text is cut and binary values show only their size. Per-user tables can be read here (the project owns the data); every query is logged in the project's activity, without its SQL. At most 120 queries per hour per project.