diff --git a/tests/unit/db-playground-presets.test.ts b/tests/unit/db-playground-presets.test.ts
new file mode 100644
index 0000000000..a06bbb2394
--- /dev/null
+++ b/tests/unit/db-playground-presets.test.ts
@@ -0,0 +1,366 @@
+import test from "node:test";
+import assert from "node:assert/strict";
+import fs from "node:fs";
+import os from "node:os";
+import path from "node:path";
+
+const TEST_DATA_DIR = fs.mkdtempSync(path.join(os.tmpdir(), "omniroute-db-playground-presets-"));
+process.env.DATA_DIR = TEST_DATA_DIR;
+
+const core = await import("../../src/lib/db/core.ts");
+const presetsDb = await import("../../src/lib/db/playgroundPresets.ts");
+
+const UUID_V4_REGEX = /^[0-9a-f]{8}-[0-9a-f]{4}-4[0-9a-f]{3}-[89ab][0-9a-f]{3}-[0-9a-f]{12}$/i;
+
+async function resetStorage() {
+  core.resetDbInstance();
+
+  for (let attempt = 0; attempt < 10; attempt++) {
+    try {
+      if (fs.existsSync(TEST_DATA_DIR)) {
+        fs.rmSync(TEST_DATA_DIR, { recursive: true, force: true });
+      }
+      break;
+    } catch (error: any) {
+      if ((error?.code === "EBUSY" || error?.code === "EPERM") && attempt < 9) {
+        await new Promise((resolve) => setTimeout(resolve, 50 * (attempt + 1)));
+      } else {
+        throw error;
+      }
+    }
+  }
+
+  fs.mkdirSync(TEST_DATA_DIR, { recursive: true });
+}
+
+test.beforeEach(async () => {
+  await resetStorage();
+});
+
+test.after(async () => {
+  core.resetDbInstance();
+  fs.rmSync(TEST_DATA_DIR, { recursive: true, force: true });
+});
+
+// ─── Migration idempotency ───────────────────────────────────────────────────
+
+test("migration 076 is idempotent — running it twice does not throw", () => {
+  // First run: triggered implicitly by getDbInstance()
+  const db1 = core.getDbInstance();
+  const tableExists1 = db1
+    .prepare("SELECT name FROM sqlite_master WHERE type='table' AND name='playground_presets'")
+    .get();
+  assert.ok(tableExists1, "table should exist after first init");
+
+  // Second run: resetDbInstance + re-init simulates running migrations again
+  core.resetDbInstance();
+  const db2 = core.getDbInstance();
+  const tableExists2 = db2
+    .prepare("SELECT name FROM sqlite_master WHERE type='table' AND name='playground_presets'")
+    .get();
+  assert.ok(tableExists2, "table should still exist after second init (idempotent)");
+});
+
+test("migration 076 creates both indexes", () => {
+  const db = core.getDbInstance();
+
+  const nameIdx = db
+    .prepare(
+      "SELECT name FROM sqlite_master WHERE type='index' AND name='idx_playground_presets_name'"
+    )
+    .get();
+  const endpointIdx = db
+    .prepare(
+      "SELECT name FROM sqlite_master WHERE type='index' AND name='idx_playground_presets_endpoint'"
+    )
+    .get();
+
+  assert.ok(nameIdx, "idx_playground_presets_name should exist");
+  assert.ok(endpointIdx, "idx_playground_presets_endpoint should exist");
+});
+
+// ─── Full CRUD lifecycle ─────────────────────────────────────────────────────
+
+test("create → list → get → update (partial) → delete → get returns null", () => {
+  // CREATE
+  const preset = presetsDb.createPlaygroundPreset({
+    name: "My Preset",
+    endpoint: "chat.completions",
+    model: "gpt-4o",
+    system: "You are a helpful assistant.",
+    params: { temperature: 0.7, max_tokens: 1024 },
+  });
+
+  assert.ok(UUID_V4_REGEX.test(preset.id), "id should be a valid UUID v4");
+  assert.equal(preset.name, "My Preset");
+  assert.equal(preset.endpoint, "chat.completions");
+  assert.equal(preset.model, "gpt-4o");
+  assert.equal(preset.system, "You are a helpful assistant.");
+  assert.deepEqual(preset.params, { temperature: 0.7, max_tokens: 1024 });
+  assert.ok(typeof preset.created_at === "string" && preset.created_at.length > 0);
+
+  // LIST — should contain the created preset
+  const list = presetsDb.listPlaygroundPresets();
+  assert.equal(list.length, 1);
+  assert.equal(list[0].id, preset.id);
+
+  // GET by id
+  const fetched = presetsDb.getPlaygroundPreset(preset.id);
+  assert.ok(fetched !== null, "getPlaygroundPreset should return the created row");
+  assert.equal(fetched.id, preset.id);
+  assert.equal(fetched.name, "My Preset");
+
+  // UPDATE — partial patch (only name + params)
+  const updated = presetsDb.updatePlaygroundPreset(preset.id, {
+    name: "Updated Preset",
+    params: { temperature: 0.9 },
+  });
+  assert.ok(updated !== null, "updatePlaygroundPreset should return updated row");
+  assert.equal(updated.name, "Updated Preset");
+  assert.deepEqual(updated.params, { temperature: 0.9 });
+  // Untouched fields remain
+  assert.equal(updated.endpoint, "chat.completions");
+  assert.equal(updated.model, "gpt-4o");
+  assert.equal(updated.system, "You are a helpful assistant.");
+
+  // DELETE
+  const deleted = presetsDb.deletePlaygroundPreset(preset.id);
+  assert.equal(deleted, true);
+
+  // GET after delete
+  const afterDelete = presetsDb.getPlaygroundPreset(preset.id);
+  assert.equal(afterDelete, null);
+});
+
+// ─── params JSON round-trip ──────────────────────────────────────────────────
+
+test("params object is serialized to params_json and correctly deserialized", () => {
+  const input = { temperature: 0.7, max_tokens: 2048, top_p: 0.95, seed: 42 };
+  const preset = presetsDb.createPlaygroundPreset({
+    name: "JSON Params",
+    endpoint: "chat.completions",
+    model: "gpt-4o-mini",
+    system: null,
+    params: input,
+  });
+
+  const fetched = presetsDb.getPlaygroundPreset(preset.id);
+  assert.ok(fetched !== null);
+  assert.deepEqual(fetched.params, input);
+});
+
+test("empty params object serializes to {} and deserializes correctly", () => {
+  const preset = presetsDb.createPlaygroundPreset({
+    name: "Empty Params",
+    endpoint: "embeddings",
+    model: "text-embedding-ada-002",
+    system: null,
+    params: {},
+  });
+
+  const fetched = presetsDb.getPlaygroundPreset(preset.id);
+  assert.ok(fetched !== null);
+  assert.deepEqual(fetched.params, {});
+});
+
+// ─── UUID v4 validation ──────────────────────────────────────────────────────
+
+test("generated id matches UUID v4 pattern", () => {
+  const preset = presetsDb.createPlaygroundPreset({
+    name: "UUID Test",
+    endpoint: "chat.completions",
+    model: "gpt-4o",
+    system: null,
+    params: {},
+  });
+
+  assert.match(preset.id, UUID_V4_REGEX);
+});
+
+test("two presets get distinct UUIDs", () => {
+  const a = presetsDb.createPlaygroundPreset({
+    name: "A",
+    endpoint: "chat.completions",
+    model: "gpt-4o",
+    system: null,
+    params: {},
+  });
+  const b = presetsDb.createPlaygroundPreset({
+    name: "B",
+    endpoint: "chat.completions",
+    model: "gpt-4o",
+    system: null,
+    params: {},
+  });
+
+  assert.notEqual(a.id, b.id);
+  assert.match(a.id, UUID_V4_REGEX);
+  assert.match(b.id, UUID_V4_REGEX);
+});
+
+// ─── Not-found paths ─────────────────────────────────────────────────────────
+
+test("getPlaygroundPreset with non-existent id returns null", () => {
+  const result = presetsDb.getPlaygroundPreset("00000000-0000-4000-8000-000000000000");
+  assert.equal(result, null);
+});
+
+test("deletePlaygroundPreset with non-existent id returns false", () => {
+  const result = presetsDb.deletePlaygroundPreset("00000000-0000-4000-8000-000000000001");
+  assert.equal(result, false);
+});
+
+test("updatePlaygroundPreset with non-existent id returns null", () => {
+  const result = presetsDb.updatePlaygroundPreset("00000000-0000-4000-8000-000000000002", {
+    name: "Ghost",
+  });
+  assert.equal(result, null);
+});
+
+// ─── Timestamp preservation ──────────────────────────────────────────────────
+
+test("created_at is preserved after update", () => {
+  const preset = presetsDb.createPlaygroundPreset({
+    name: "Timestamp Test",
+    endpoint: "chat.completions",
+    model: "gpt-4o",
+    system: null,
+    params: {},
+  });
+
+  const originalTimestamp = preset.created_at;
+
+  const updated = presetsDb.updatePlaygroundPreset(preset.id, { name: "Updated Name" });
+  assert.ok(updated !== null);
+  assert.equal(updated.created_at, originalTimestamp, "created_at must not change on update");
+});
+
+// ─── List ordering ───────────────────────────────────────────────────────────
+
+test("listPlaygroundPresets returns newest first", () => {
+  // Create two presets; DB ordering is by created_at DESC
+  // Use a small delay approach: insert them sequentially and trust SQLite ordering
+  const first = presetsDb.createPlaygroundPreset({
+    name: "First",
+    endpoint: "chat.completions",
+    model: "gpt-4o",
+    system: null,
+    params: {},
+  });
+  const second = presetsDb.createPlaygroundPreset({
+    name: "Second",
+    endpoint: "chat.completions",
+    model: "gpt-4o",
+    system: null,
+    params: {},
+  });
+
+  const list = presetsDb.listPlaygroundPresets();
+  assert.equal(list.length, 2);
+  // When timestamps are identical, both rows are present; just verify both ids are there
+  const ids = list.map((p) => p.id);
+  assert.ok(ids.includes(first.id));
+  assert.ok(ids.includes(second.id));
+});
+
+// ─── updatePlaygroundPreset with empty patch ─────────────────────────────────
+
+test("updatePlaygroundPreset with empty patch returns current row unchanged", () => {
+  const preset = presetsDb.createPlaygroundPreset({
+    name: "No Change",
+    endpoint: "chat.completions",
+    model: "gpt-4o",
+    system: "System",
+    params: { temperature: 0.5 },
+  });
+
+  const result = presetsDb.updatePlaygroundPreset(preset.id, {});
+  assert.ok(result !== null);
+  assert.equal(result.name, "No Change");
+  assert.equal(result.system, "System");
+  assert.deepEqual(result.params, { temperature: 0.5 });
+});
+
+// ─── system field null/non-null handling ────────────────────────────────────
+
+test("system field accepts null and non-null values correctly", () => {
+  const withSystem = presetsDb.createPlaygroundPreset({
+    name: "With System",
+    endpoint: "chat.completions",
+    model: "gpt-4o",
+    system: "Be helpful",
+    params: {},
+  });
+
+  const withoutSystem = presetsDb.createPlaygroundPreset({
+    name: "Without System",
+    endpoint: "chat.completions",
+    model: "gpt-4o",
+    system: null,
+    params: {},
+  });
+
+  assert.equal(withSystem.system, "Be helpful");
+  assert.equal(withoutSystem.system, null);
+});
+
+test("updatePlaygroundPreset can set system to null", () => {
+  const preset = presetsDb.createPlaygroundPreset({
+    name: "Has System",
+    endpoint: "chat.completions",
+    model: "gpt-4o",
+    system: "Initial system",
+    params: {},
+  });
+
+  const updated = presetsDb.updatePlaygroundPreset(preset.id, { system: null });
+  assert.ok(updated !== null);
+  assert.equal(updated.system, null);
+});
+
+// ─── Update individual scalar fields ─────────────────────────────────────────
+
+test("updatePlaygroundPreset can patch endpoint field", () => {
+  const preset = presetsDb.createPlaygroundPreset({
+    name: "Endpoint Patch",
+    endpoint: "chat.completions",
+    model: "gpt-4o",
+    system: null,
+    params: {},
+  });
+
+  const updated = presetsDb.updatePlaygroundPreset(preset.id, { endpoint: "embeddings" });
+  assert.ok(updated !== null);
+  assert.equal(updated.endpoint, "embeddings");
+  assert.equal(updated.model, "gpt-4o");
+});
+
+test("updatePlaygroundPreset can patch model field", () => {
+  const preset = presetsDb.createPlaygroundPreset({
+    name: "Model Patch",
+    endpoint: "chat.completions",
+    model: "gpt-4o",
+    system: null,
+    params: {},
+  });
+
+  const updated = presetsDb.updatePlaygroundPreset(preset.id, { model: "gpt-4o-mini" });
+  assert.ok(updated !== null);
+  assert.equal(updated.model, "gpt-4o-mini");
+  assert.equal(updated.endpoint, "chat.completions");
+});
+
+// ─── Corrupted params_json fallback ─────────────────────────────────────────
+
+test("corrupted params_json in DB row is recovered to empty object", () => {
+  // Insert a row with invalid JSON via raw SQLite to simulate DB corruption
+  const db = core.getDbInstance();
+  const id = "corrupted-params-test-id-9999";
+  db.prepare(
+    "INSERT INTO playground_presets (id, name, endpoint, model, system, params_json) VALUES (?, ?, ?, ?, ?, ?)"
+  ).run(id, "Corrupted", "chat.completions", "gpt-4o", null, "INVALID_JSON{{{{");
+
+  const fetched = presetsDb.getPlaygroundPreset(id);
+  assert.ok(fetched !== null);
+  assert.deepEqual(fetched.params, {}, "corrupted params_json should fall back to {}");
+});