Index: iknow-api/Controllers/DbHealthController.cs
===================================================================
--- iknow-api/Controllers/DbHealthController.cs	(revision ea405569ef29f56fbfc4d77708b6b3faf9286097)
+++ iknow-api/Controllers/DbHealthController.cs	(revision ea405569ef29f56fbfc4d77708b6b3faf9286097)
@@ -0,0 +1,49 @@
+using iknow_api.Data;
+using Microsoft.AspNetCore.Mvc;
+using Microsoft.EntityFrameworkCore;
+
+namespace iknow_api.Controllers;
+
+[ApiController]
+[Route("[controller]")]
+public class DbHealthController(AppDbContext db) : ControllerBase
+{
+    /// <summary>
+    /// Verifies that the SSH tunnel is up, the DB credentials work, and that
+    /// the entity mapping matches the schema created by sql/ddl.sql.
+    /// </summary>
+    [HttpGet]
+    public async Task<IActionResult> Get()
+    {
+        try
+        {
+            // EF projects SqlQuery onto a column named "Value", hence the alias.
+            var version = await db.Database
+                .SqlQuery<string>($"SELECT version() AS \"Value\"")
+                .SingleAsync();
+
+            return Ok(new
+            {
+                connected = true,
+                server = version,
+                counts = new
+                {
+                    users = await db.User.CountAsync(),
+                    subjects = await db.Subjects.CountAsync(),
+                    enrolledSemesters = await db.EnrolledSemesters.CountAsync(),
+                    semesterSubjects = await db.SemesterSubjects.CountAsync(),
+                    passedSubjects = await db.PassedSubjects.CountAsync(),
+                }
+            });
+        }
+        catch (Exception ex)
+        {
+            return StatusCode(503, new
+            {
+                connected = false,
+                error = ex.Message,
+                hint = "Is tunnel_scripta.cmd running and listening on localhost:9999?"
+            });
+        }
+    }
+}