diff --git a/apps/api/src/modules/search/domain/search-query.js b/apps/api/src/modules/search/domain/search-query.js
new file mode 100644
index 0000000..f71cdb0
--- /dev/null
+++ b/apps/api/src/modules/search/domain/search-query.js
@@ -0,0 +1,70 @@
+function requiredString(value, fieldName) {
+  if (typeof value !== 'string') {
+    throw new Error(`${fieldName} must be a string.`);
+  }
+
+  return value;
+}
+
+export function normalizeSearchQuery(value) {
+  return requiredString(value, 'Search query')
+    .trim()
+    .normalize('NFKC')
+    .replace(/[^\p{L}\p{N}\s]+/gu, ' ')
+    .replace(/\s+/g, ' ')
+    .toLowerCase();
+}
+
+export function createSearchQuery({
+  query = '',
+  category,
+  minPriceMinor,
+  maxPriceMinor,
+  page = 1,
+  limit = 20,
+  includeSold = false,
+}) {
+  const text = normalizeSearchQuery(query);
+
+  if (!Number.isInteger(page) || page < 1) {
+    throw new Error('page must be >= 1');
+  }
+
+  if (!Number.isInteger(limit) || limit < 1 || limit > 100) {
+    throw new Error('limit must be between 1 and 100');
+  }
+
+  if (typeof minPriceMinor !== 'undefined' && (!Number.isInteger(minPriceMinor) || minPriceMinor < 0)) {
+    throw new Error('minPriceMinor must be a non-negative integer');
+  }
+
+  if (typeof maxPriceMinor !== 'undefined' && (!Number.isInteger(maxPriceMinor) || maxPriceMinor < 0)) {
+    throw new Error('maxPriceMinor must be a non-negative integer');
+  }
+
+  if (
+    typeof minPriceMinor !== 'undefined' &&
+    typeof maxPriceMinor !== 'undefined' &&
+    minPriceMinor > maxPriceMinor
+  ) {
+    throw new Error('minPriceMinor must be <= maxPriceMinor');
+  }
+
+  return {
+    text,
+    ...(typeof category === 'string' && category.trim().length > 0 ? { category: category.trim() } : {}),
+    ...(typeof minPriceMinor === 'number' ? { minPriceMinor } : {}),
+    ...(typeof maxPriceMinor === 'number' ? { maxPriceMinor } : {}),
+    page,
+    limit,
+    includeSold,
+  };
+}
+
+export function buildSearchFilters({ includeSold = false, status = 'AVAILABLE', sort = ['recently_added'] }) {
+  return {
+    status: includeSold ? 'ALL' : status,
+    includeSold,
+    sort,
+  };
+}
diff --git a/apps/api/tests/domain/search-query.test.js b/apps/api/tests/domain/search-query.test.js
new file mode 100644
index 0000000..7fc06ba
--- /dev/null
+++ b/apps/api/tests/domain/search-query.test.js
@@ -0,0 +1,46 @@
+import assert from 'node:assert/strict';
+import test from 'node:test';
+
+import {
+  buildSearchFilters,
+  createSearchQuery,
+  normalizeSearchQuery,
+} from '../../src/modules/search/domain/search-query.js';
+
+test('normalizes a public search query and keeps filter values within bounds', () => {
+  const query = createSearchQuery({
+    query: '  Charizard   ex  ',
+    category: 'Cards',
+    minPriceMinor: 1000,
+    maxPriceMinor: 5000,
+    page: 1,
+    limit: 20,
+    includeSold: false,
+  });
+
+  assert.equal(query.text, 'charizard ex');
+  assert.equal(query.category, 'Cards');
+  assert.equal(query.minPriceMinor, 1000);
+  assert.equal(query.maxPriceMinor, 5000);
+  assert.equal(query.page, 1);
+  assert.equal(query.limit, 20);
+  assert.equal(query.includeSold, false);
+});
+
+test('rejects invalid pagination and price boundaries', () => {
+  assert.throws(() => createSearchQuery({ query: 'abc', page: 0, limit: 20 }), /page must be >= 1/);
+  assert.throws(() => createSearchQuery({ query: 'abc', minPriceMinor: 5000, maxPriceMinor: 1000 }), /minPriceMinor must be <= maxPriceMinor/);
+  assert.throws(() => createSearchQuery({ query: 'abc', limit: 0 }), /limit must be between 1 and 100/);
+});
+
+test('builds a public query filter set that hides sold items by default', () => {
+  const filters = buildSearchFilters({ includeSold: false });
+
+  assert.equal(filters.status, 'AVAILABLE');
+  assert.equal(filters.includeSold, false);
+  assert.deepEqual(filters.sort, ['recently_added']);
+});
+
+test('normalizes whitespace and punctuation in free-text search terms', () => {
+  assert.equal(normalizeSearchQuery('  Pikachu #199 / holo  '), 'pikachu 199 holo');
+});