diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
new file mode 100644
index 0000000..754d3d0
--- /dev/null
+++ b/.github/workflows/ci.yml
@@ -0,0 +1,33 @@
+name: CI
+
+on:
+  push:
+    branches: [main]
+  pull_request:
+    branches: [main]
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        sdk: [stable, beta]
+    steps:
+      - uses: actions/checkout@v4
+      - uses: dart-lang/setup-dart@v1
+        with:
+          sdk: ${{ matrix.sdk }}
+      - run: dart pub get
+      - run: dart analyze
+      - run: dart test
+      - run: dart format --set-exit-if-changed .
+
+  publish-check:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: dart-lang/setup-dart@v1
+        with:
+          sdk: stable
+      - run: dart pub get
+      - run: dart pub publish --dry-run
diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..a909c98
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,27 @@
+# Dart/Flutter
+.dart_tool/
+.packages
+build/
+pubspec.lock
+doc/api/
+
+# IDE
+.idea/
+*.iml
+.vscode/
+
+# OS
+.DS_Store
+Thumbs.db
+
+# AI agents
+.claude/
+.vscode/*
+.codex/
+.cursor/
+.aider/
+.aider.chat.history.md
+.continue/
+.windsurf/
+.gemini/
+.codeium/
diff --git a/CHANGELOG.md b/CHANGELOG.md
new file mode 100644
index 0000000..f3add7a
--- /dev/null
+++ b/CHANGELOG.md
@@ -0,0 +1,16 @@
+# Changelog
+
+All notable changes to this project will be documented in this file.
+
+## 1.0.0
+
+### Added
+
+- Umm al-Qura (UAQ) engine: table-driven conversion for Hijri years 1318-1500
+- FCNA engine: astronomical new moon calculation using Meeus Ch. 49
+- Pluggable engine registry with `registerCalendar()` and `getCalendar()`
+- Top-level convenience functions: `toHijri()`, `toGregorian()`, `isValidHijriDate()`, `daysInHijriMonth()`
+- Hijri month names in long, medium, and short forms
+- Hijri weekday names in long, short, and numeric forms
+- Full 184-entry Umm al-Qura reference table (1318-1501 H)
+- Zero external dependencies
diff --git a/README.md b/README.md
new file mode 100644
index 0000000..7ae51aa
--- /dev/null
+++ b/README.md
@@ -0,0 +1,134 @@
+# hijri_core
+
+[![pub package](https://img.shields.io/pub/v/hijri_core.svg)](https://pub.dev/packages/hijri_core)
+[![CI](https://github.com/acamarata/hijri-core-dart/actions/workflows/ci.yml/badge.svg)](https://github.com/acamarata/hijri-core-dart/actions/workflows/ci.yml)
+[![License: MIT](https://img.shields.io/badge/License-MIT-blue.svg)](LICENSE)
+
+Hijri/Gregorian calendar conversion for Dart and Flutter. Zero dependencies.
+
+## Installation
+
+```yaml
+dependencies:
+  hijri_core: ^1.0.0
+```
+
+## Quick Start
+
+```dart
+import 'package:hijri_core/hijri_core.dart';
+
+// Gregorian to Hijri (Umm al-Qura by default)
+final hijri = toHijri(DateTime.utc(2025, 3, 1));
+print('${hijri!.hy}/${hijri.hm}/${hijri.hd}'); // 1446/9/1
+
+// Hijri to Gregorian
+final greg = toGregorian(1446, 9, 1);
+print(greg!.toIso8601String().substring(0, 10)); // 2025-03-01
+
+// Use FCNA calendar instead
+final fcna = toHijri(
+  DateTime.utc(2025, 3, 1),
+  options: const ConversionOptions(calendar: 'fcna'),
+);
+
+// Validate a Hijri date
+final valid = isValidHijriDate(1444, 9, 1); // true
+
+// Days in a Hijri month
+final days = daysInHijriMonth(1444, 9); // 29
+```
+
+## API
+
+### Top-Level Functions
+
+| Function | Description |
+| --- | --- |
+| `toHijri(DateTime date, {ConversionOptions? options})` | Convert Gregorian to Hijri. Returns `HijriDate?`. |
+| `toGregorian(int hy, int hm, int hd, {ConversionOptions? options})` | Convert Hijri to Gregorian. Returns `DateTime?` (UTC). |
+| `isValidHijriDate(int hy, int hm, int hd, {ConversionOptions? options})` | Check if a Hijri date is valid. Returns `bool`. |
+| `daysInHijriMonth(int hy, int hm, {ConversionOptions? options})` | Days in a Hijri month (29 or 30). Throws `RangeError` if out of range. |
+
+### Registry Functions
+
+| Function | Description |
+| --- | --- |
+| `registerCalendar(String name, CalendarEngine engine)` | Register a custom calendar engine. |
+| `getCalendar(String name)` | Retrieve a registered engine by name. |
+| `listCalendars()` | List all registered engine names. |
+
+### Data
+
+| Export | Description |
+| --- | --- |
+| `hDatesTable` | 184-entry Umm al-Qura reference table (Hijri 1318-1501). |
+| `hmLong`, `hmMedium`, `hmShort` | Hijri month names (12 entries each). |
+| `hwLong`, `hwShort`, `hwNumeric` | Hijri weekday names (7 entries each). |
+
+## Engines
+
+### UAQ (Umm al-Qura)
+
+The official Saudi Arabian Islamic calendar. Table-driven conversions covering Hijri years 1318-1500 (Gregorian 1900-2076). Returns `null` for dates outside that range.
+
+This is the default engine.
+
+### FCNA (Fiqh Council of North America)
+
+Astronomical calculation using Meeus Chapter 49 new moon algorithm. The FCNA criterion: if the new moon conjunction occurs before 12:00 noon UTC on day D, the new Hijri month begins at midnight starting day D+1. Otherwise it begins at midnight starting day D+2.
+
+No fixed date range. Works for any Hijri year >= 1.
+
+```dart
+final h = toHijri(
+  DateTime.utc(2025, 3, 1),
+  options: const ConversionOptions(calendar: 'fcna'),
+);
+```
+
+## Custom Engine
+
+Implement the `CalendarEngine` abstract class and register it:
+
+```dart
+class MyEngine extends CalendarEngine {
+  @override
+  String get id => 'custom';
+
+  @override
+  HijriDate? toHijri(DateTime date) { /* ... */ }
+
+  @override
+  DateTime? toGregorian(int hy, int hm, int hd) { /* ... */ }
+
+  @override
+  bool isValid(int hy, int hm, int hd) { /* ... */ }
+
+  @override
+  int daysInMonth(int hy, int hm) { /* ... */ }
+}
+
+registerCalendar('custom', MyEngine());
+
+final h = toHijri(
+  DateTime.utc(2025, 1, 1),
+  options: const ConversionOptions(calendar: 'custom'),
+);
+```
+
+## Compatibility
+
+- Dart SDK >= 3.7.0
+- Works with Flutter
+- Zero external dependencies
+
+## Related Packages
+
+- [hijri-core](https://www.npmjs.com/package/hijri-core) (TypeScript/npm)
+- [nrel-spa](https://www.npmjs.com/package/nrel-spa) (Solar position algorithm)
+- [pray-calc](https://www.npmjs.com/package/pray-calc) (Islamic prayer times)
+
+## License
+
+MIT. Copyright (c) 2026 Aric Camarata.
diff --git a/analysis_options.yaml b/analysis_options.yaml
new file mode 100644
index 0000000..572dd23
--- /dev/null
+++ b/analysis_options.yaml
@@ -0,0 +1 @@
+include: package:lints/recommended.yaml
diff --git a/lib/hijri_core.dart b/lib/hijri_core.dart
new file mode 100644
index 0000000..3f5b06f
--- /dev/null
+++ b/lib/hijri_core.dart
@@ -0,0 +1,28 @@
+/// Hijri/Gregorian calendar conversion for Dart and Flutter.
+///
+/// Pluggable engine system with built-in Umm al-Qura (UAQ) and FCNA calendars.
+/// Zero dependencies.
+library;
+
+// Types
+export 'src/types.dart';
+
+// Constants
+export 'src/constants.dart';
+
+// Data
+export 'src/data.dart';
+
+// Registry
+export 'src/registry.dart';
+
+// Names
+export 'src/names/months.dart';
+export 'src/names/weekdays.dart';
+
+// Engines (for direct access)
+export 'src/engines/uaq.dart' show uaqEngine;
+export 'src/engines/fcna.dart' show fcnaEngine;
+
+// Top-level convenience API
+export 'src/hijri_core_api.dart';
diff --git a/lib/src/constants.dart b/lib/src/constants.dart
new file mode 100644
index 0000000..c21c0e7
--- /dev/null
+++ b/lib/src/constants.dart
@@ -0,0 +1,5 @@
+/// Milliseconds in one day.
+const int msPerDay = 86400000;
+
+/// Number of months in a Hijri year.
+const int monthsPerYear = 12;
diff --git a/lib/src/data.dart b/lib/src/data.dart
new file mode 100644
index 0000000..f7cf18e
--- /dev/null
+++ b/lib/src/data.dart
@@ -0,0 +1,192 @@
+import 'types.dart';
+
+/// Umm al-Qura reference table: Hijri years 1318-1501.
+/// Each entry records the 1 Muharram Gregorian date and a 12-bit days-per-month
+/// bitmask. Bit i (0-indexed from bit 0) corresponds to month i+1: 1 = 30 days,
+/// 0 = 29 days. The final sentinel entry (hy 1501, dpm 0) marks the upper bound.
+final List<HijriYearRecord> hDatesTable = const [
+  HijriYearRecord(hy: 1318, dpm: 0x02ea, gy: 1900, gm: 4, gd: 30),
+  HijriYearRecord(hy: 1319, dpm: 0x06e9, gy: 1901, gm: 4, gd: 19),
+  HijriYearRecord(hy: 1320, dpm: 0x0ed2, gy: 1902, gm: 4, gd: 9),
+  HijriYearRecord(hy: 1321, dpm: 0x0ea4, gy: 1903, gm: 3, gd: 30),
+  HijriYearRecord(hy: 1322, dpm: 0x0d4a, gy: 1904, gm: 3, gd: 18),
+  HijriYearRecord(hy: 1323, dpm: 0x0a96, gy: 1905, gm: 3, gd: 7),
+  HijriYearRecord(hy: 1324, dpm: 0x0536, gy: 1906, gm: 2, gd: 24),
+  HijriYearRecord(hy: 1325, dpm: 0x0ab5, gy: 1907, gm: 2, gd: 13),
+  HijriYearRecord(hy: 1326, dpm: 0x0daa, gy: 1908, gm: 2, gd: 3),
+  HijriYearRecord(hy: 1327, dpm: 0x0ba4, gy: 1909, gm: 1, gd: 23),
+  HijriYearRecord(hy: 1328, dpm: 0x0b49, gy: 1910, gm: 1, gd: 12),
+  HijriYearRecord(hy: 1329, dpm: 0x0a93, gy: 1911, gm: 1, gd: 1),
+  HijriYearRecord(hy: 1330, dpm: 0x052b, gy: 1911, gm: 12, gd: 21),
+  HijriYearRecord(hy: 1331, dpm: 0x0a57, gy: 1912, gm: 12, gd: 9),
+  HijriYearRecord(hy: 1332, dpm: 0x04b6, gy: 1913, gm: 11, gd: 29),
+  HijriYearRecord(hy: 1333, dpm: 0x0ab5, gy: 1914, gm: 11, gd: 18),
+  HijriYearRecord(hy: 1334, dpm: 0x05aa, gy: 1915, gm: 11, gd: 8),
+  HijriYearRecord(hy: 1335, dpm: 0x0d55, gy: 1916, gm: 10, gd: 27),
+  HijriYearRecord(hy: 1336, dpm: 0x0d2a, gy: 1917, gm: 10, gd: 17),
+  HijriYearRecord(hy: 1337, dpm: 0x0a56, gy: 1918, gm: 10, gd: 6),
+  HijriYearRecord(hy: 1338, dpm: 0x04ae, gy: 1919, gm: 9, gd: 25),
+  HijriYearRecord(hy: 1339, dpm: 0x095d, gy: 1920, gm: 9, gd: 13),
+  HijriYearRecord(hy: 1340, dpm: 0x02ec, gy: 1921, gm: 9, gd: 3),
+  HijriYearRecord(hy: 1341, dpm: 0x06d5, gy: 1922, gm: 8, gd: 23),
+  HijriYearRecord(hy: 1342, dpm: 0x06aa, gy: 1923, gm: 8, gd: 13),
+  HijriYearRecord(hy: 1343, dpm: 0x0555, gy: 1924, gm: 8, gd: 1),
+  HijriYearRecord(hy: 1344, dpm: 0x04ab, gy: 1925, gm: 7, gd: 21),
+  HijriYearRecord(hy: 1345, dpm: 0x095b, gy: 1926, gm: 7, gd: 10),
+  HijriYearRecord(hy: 1346, dpm: 0x02ba, gy: 1927, gm: 6, gd: 30),
+  HijriYearRecord(hy: 1347, dpm: 0x0575, gy: 1928, gm: 6, gd: 18),
+  HijriYearRecord(hy: 1348, dpm: 0x0bb2, gy: 1929, gm: 6, gd: 8),
+  HijriYearRecord(hy: 1349, dpm: 0x0764, gy: 1930, gm: 5, gd: 29),
+  HijriYearRecord(hy: 1350, dpm: 0x0749, gy: 1931, gm: 5, gd: 18),
+  HijriYearRecord(hy: 1351, dpm: 0x0655, gy: 1932, gm: 5, gd: 6),
+  HijriYearRecord(hy: 1352, dpm: 0x02ab, gy: 1933, gm: 4, gd: 25),
+  HijriYearRecord(hy: 1353, dpm: 0x055b, gy: 1934, gm: 4, gd: 14),
+  HijriYearRecord(hy: 1354, dpm: 0x0ada, gy: 1935, gm: 4, gd: 4),
+  HijriYearRecord(hy: 1355, dpm: 0x06d4, gy: 1936, gm: 3, gd: 24),
+  HijriYearRecord(hy: 1356, dpm: 0x0ec9, gy: 1937, gm: 3, gd: 13),
+  HijriYearRecord(hy: 1357, dpm: 0x0d92, gy: 1938, gm: 3, gd: 3),
+  HijriYearRecord(hy: 1358, dpm: 0x0d25, gy: 1939, gm: 2, gd: 20),
+  HijriYearRecord(hy: 1359, dpm: 0x0a4d, gy: 1940, gm: 2, gd: 9),
+  HijriYearRecord(hy: 1360, dpm: 0x02ad, gy: 1941, gm: 1, gd: 28),
+  HijriYearRecord(hy: 1361, dpm: 0x056d, gy: 1942, gm: 1, gd: 17),
+  HijriYearRecord(hy: 1362, dpm: 0x0b6a, gy: 1943, gm: 1, gd: 7),
+  HijriYearRecord(hy: 1363, dpm: 0x0b52, gy: 1943, gm: 12, gd: 28),
+  HijriYearRecord(hy: 1364, dpm: 0x0aa5, gy: 1944, gm: 12, gd: 16),
+  HijriYearRecord(hy: 1365, dpm: 0x0a4b, gy: 1945, gm: 12, gd: 5),
+  HijriYearRecord(hy: 1366, dpm: 0x0497, gy: 1946, gm: 11, gd: 24),
+  HijriYearRecord(hy: 1367, dpm: 0x0937, gy: 1947, gm: 11, gd: 13),
+  HijriYearRecord(hy: 1368, dpm: 0x02b6, gy: 1948, gm: 11, gd: 2),
+  HijriYearRecord(hy: 1369, dpm: 0x0575, gy: 1949, gm: 10, gd: 22),
+  HijriYearRecord(hy: 1370, dpm: 0x0d6a, gy: 1950, gm: 10, gd: 12),
+  HijriYearRecord(hy: 1371, dpm: 0x0d52, gy: 1951, gm: 10, gd: 2),
+  HijriYearRecord(hy: 1372, dpm: 0x0a96, gy: 1952, gm: 9, gd: 20),
+  HijriYearRecord(hy: 1373, dpm: 0x092d, gy: 1953, gm: 9, gd: 9),
+  HijriYearRecord(hy: 1374, dpm: 0x025d, gy: 1954, gm: 8, gd: 29),
+  HijriYearRecord(hy: 1375, dpm: 0x04dd, gy: 1955, gm: 8, gd: 18),
+  HijriYearRecord(hy: 1376, dpm: 0x0ada, gy: 1956, gm: 8, gd: 7),
+  HijriYearRecord(hy: 1377, dpm: 0x05d4, gy: 1957, gm: 7, gd: 28),
+  HijriYearRecord(hy: 1378, dpm: 0x0da9, gy: 1958, gm: 7, gd: 17),
+  HijriYearRecord(hy: 1379, dpm: 0x0d52, gy: 1959, gm: 7, gd: 7),
+  HijriYearRecord(hy: 1380, dpm: 0x0aaa, gy: 1960, gm: 6, gd: 25),
+  HijriYearRecord(hy: 1381, dpm: 0x04d6, gy: 1961, gm: 6, gd: 14),
+  HijriYearRecord(hy: 1382, dpm: 0x09b6, gy: 1962, gm: 6, gd: 3),
+  HijriYearRecord(hy: 1383, dpm: 0x0374, gy: 1963, gm: 5, gd: 24),
+  HijriYearRecord(hy: 1384, dpm: 0x0769, gy: 1964, gm: 5, gd: 12),
+  HijriYearRecord(hy: 1385, dpm: 0x0752, gy: 1965, gm: 5, gd: 2),
+  HijriYearRecord(hy: 1386, dpm: 0x06a5, gy: 1966, gm: 4, gd: 21),
+  HijriYearRecord(hy: 1387, dpm: 0x054b, gy: 1967, gm: 4, gd: 10),
+  HijriYearRecord(hy: 1388, dpm: 0x0aab, gy: 1968, gm: 3, gd: 29),
+  HijriYearRecord(hy: 1389, dpm: 0x055a, gy: 1969, gm: 3, gd: 19),
+  HijriYearRecord(hy: 1390, dpm: 0x0ad5, gy: 1970, gm: 3, gd: 8),
+  HijriYearRecord(hy: 1391, dpm: 0x0dd2, gy: 1971, gm: 2, gd: 26),
+  HijriYearRecord(hy: 1392, dpm: 0x0da4, gy: 1972, gm: 2, gd: 16),
+  HijriYearRecord(hy: 1393, dpm: 0x0d49, gy: 1973, gm: 2, gd: 4),
+  HijriYearRecord(hy: 1394, dpm: 0x0a95, gy: 1974, gm: 1, gd: 24),
+  HijriYearRecord(hy: 1395, dpm: 0x052d, gy: 1975, gm: 1, gd: 13),
+  HijriYearRecord(hy: 1396, dpm: 0x0a5d, gy: 1976, gm: 1, gd: 2),
+  HijriYearRecord(hy: 1397, dpm: 0x055a, gy: 1976, gm: 12, gd: 22),
+  HijriYearRecord(hy: 1398, dpm: 0x0ad5, gy: 1977, gm: 12, gd: 11),
+  HijriYearRecord(hy: 1399, dpm: 0x06aa, gy: 1978, gm: 12, gd: 1),
+  HijriYearRecord(hy: 1400, dpm: 0x0695, gy: 1979, gm: 11, gd: 20),
+  HijriYearRecord(hy: 1401, dpm: 0x052b, gy: 1980, gm: 11, gd: 8),
+  HijriYearRecord(hy: 1402, dpm: 0x0a57, gy: 1981, gm: 10, gd: 28),
+  HijriYearRecord(hy: 1403, dpm: 0x04ae, gy: 1982, gm: 10, gd: 18),
+  HijriYearRecord(hy: 1404, dpm: 0x0976, gy: 1983, gm: 10, gd: 7),
+  HijriYearRecord(hy: 1405, dpm: 0x056c, gy: 1984, gm: 9, gd: 26),
+  HijriYearRecord(hy: 1406, dpm: 0x0b55, gy: 1985, gm: 9, gd: 15),
+  HijriYearRecord(hy: 1407, dpm: 0x0aaa, gy: 1986, gm: 9, gd: 5),
+  HijriYearRecord(hy: 1408, dpm: 0x0a55, gy: 1987, gm: 8, gd: 25),
+  HijriYearRecord(hy: 1409, dpm: 0x04ad, gy: 1988, gm: 8, gd: 13),
+  HijriYearRecord(hy: 1410, dpm: 0x095d, gy: 1989, gm: 8, gd: 2),
+  HijriYearRecord(hy: 1411, dpm: 0x02da, gy: 1990, gm: 7, gd: 23),
+  HijriYearRecord(hy: 1412, dpm: 0x05d9, gy: 1991, gm: 7, gd: 12),
+  HijriYearRecord(hy: 1413, dpm: 0x0db2, gy: 1992, gm: 7, gd: 1),
+  HijriYearRecord(hy: 1414, dpm: 0x0ba4, gy: 1993, gm: 6, gd: 21),
+  HijriYearRecord(hy: 1415, dpm: 0x0b4a, gy: 1994, gm: 6, gd: 10),
+  HijriYearRecord(hy: 1416, dpm: 0x0a55, gy: 1995, gm: 5, gd: 30),
+  HijriYearRecord(hy: 1417, dpm: 0x02b5, gy: 1996, gm: 5, gd: 18),
+  HijriYearRecord(hy: 1418, dpm: 0x0575, gy: 1997, gm: 5, gd: 7),
+  HijriYearRecord(hy: 1419, dpm: 0x0b6a, gy: 1998, gm: 4, gd: 27),
+  HijriYearRecord(hy: 1420, dpm: 0x0bd2, gy: 1999, gm: 4, gd: 17),
+  HijriYearRecord(hy: 1421, dpm: 0x0bc4, gy: 2000, gm: 4, gd: 6),
+  HijriYearRecord(hy: 1422, dpm: 0x0b89, gy: 2001, gm: 3, gd: 26),
+  HijriYearRecord(hy: 1423, dpm: 0x0a95, gy: 2002, gm: 3, gd: 15),
+  HijriYearRecord(hy: 1424, dpm: 0x052d, gy: 2003, gm: 3, gd: 4),
+  HijriYearRecord(hy: 1425, dpm: 0x05ad, gy: 2004, gm: 2, gd: 21),
+  HijriYearRecord(hy: 1426, dpm: 0x0b6a, gy: 2005, gm: 2, gd: 10),
+  HijriYearRecord(hy: 1427, dpm: 0x06d4, gy: 2006, gm: 1, gd: 31),
+  HijriYearRecord(hy: 1428, dpm: 0x0dc9, gy: 2007, gm: 1, gd: 20),
+  HijriYearRecord(hy: 1429, dpm: 0x0d92, gy: 2008, gm: 1, gd: 10),
+  HijriYearRecord(hy: 1430, dpm: 0x0aa6, gy: 2008, gm: 12, gd: 29),
+  HijriYearRecord(hy: 1431, dpm: 0x0956, gy: 2009, gm: 12, gd: 18),
+  HijriYearRecord(hy: 1432, dpm: 0x02ae, gy: 2010, gm: 12, gd: 7),
+  HijriYearRecord(hy: 1433, dpm: 0x056d, gy: 2011, gm: 11, gd: 26),
+  HijriYearRecord(hy: 1434, dpm: 0x036a, gy: 2012, gm: 11, gd: 15),
+  HijriYearRecord(hy: 1435, dpm: 0x0b55, gy: 2013, gm: 11, gd: 4),
+  HijriYearRecord(hy: 1436, dpm: 0x0aaa, gy: 2014, gm: 10, gd: 25),
+  HijriYearRecord(hy: 1437, dpm: 0x094d, gy: 2015, gm: 10, gd: 14),
+  HijriYearRecord(hy: 1438, dpm: 0x049d, gy: 2016, gm: 10, gd: 2),
+  HijriYearRecord(hy: 1439, dpm: 0x095d, gy: 2017, gm: 9, gd: 21),
+  HijriYearRecord(hy: 1440, dpm: 0x02ba, gy: 2018, gm: 9, gd: 11),
+  HijriYearRecord(hy: 1441, dpm: 0x05b5, gy: 2019, gm: 8, gd: 31),
+  HijriYearRecord(hy: 1442, dpm: 0x05aa, gy: 2020, gm: 8, gd: 20),
+  HijriYearRecord(hy: 1443, dpm: 0x0d55, gy: 2021, gm: 8, gd: 9),
+  HijriYearRecord(hy: 1444, dpm: 0x0a9a, gy: 2022, gm: 7, gd: 30),
+  HijriYearRecord(hy: 1445, dpm: 0x092e, gy: 2023, gm: 7, gd: 19),
+  HijriYearRecord(hy: 1446, dpm: 0x026e, gy: 2024, gm: 7, gd: 7),
+  HijriYearRecord(hy: 1447, dpm: 0x055d, gy: 2025, gm: 6, gd: 26),
+  HijriYearRecord(hy: 1448, dpm: 0x0ada, gy: 2026, gm: 6, gd: 16),
+  HijriYearRecord(hy: 1449, dpm: 0x06d4, gy: 2027, gm: 6, gd: 6),
+  HijriYearRecord(hy: 1450, dpm: 0x06a5, gy: 2028, gm: 5, gd: 25),
+  HijriYearRecord(hy: 1451, dpm: 0x054b, gy: 2029, gm: 5, gd: 14),
+  HijriYearRecord(hy: 1452, dpm: 0x0a97, gy: 2030, gm: 5, gd: 3),
+  HijriYearRecord(hy: 1453, dpm: 0x054e, gy: 2031, gm: 4, gd: 23),
+  HijriYearRecord(hy: 1454, dpm: 0x0aae, gy: 2032, gm: 4, gd: 11),
+  HijriYearRecord(hy: 1455, dpm: 0x05ac, gy: 2033, gm: 4, gd: 1),
+  HijriYearRecord(hy: 1456, dpm: 0x0ba9, gy: 2034, gm: 3, gd: 21),
+  HijriYearRecord(hy: 1457, dpm: 0x0d92, gy: 2035, gm: 3, gd: 11),
+  HijriYearRecord(hy: 1458, dpm: 0x0b25, gy: 2036, gm: 2, gd: 28),
+  HijriYearRecord(hy: 1459, dpm: 0x064b, gy: 2037, gm: 2, gd: 16),
+  HijriYearRecord(hy: 1460, dpm: 0x0cab, gy: 2038, gm: 2, gd: 5),
+  HijriYearRecord(hy: 1461, dpm: 0x055a, gy: 2039, gm: 1, gd: 26),
+  HijriYearRecord(hy: 1462, dpm: 0x0b55, gy: 2040, gm: 1, gd: 15),
+  HijriYearRecord(hy: 1463, dpm: 0x06d2, gy: 2041, gm: 1, gd: 4),
+  HijriYearRecord(hy: 1464, dpm: 0x0ea5, gy: 2041, gm: 12, gd: 24),
+  HijriYearRecord(hy: 1465, dpm: 0x0e4a, gy: 2042, gm: 12, gd: 14),
+  HijriYearRecord(hy: 1466, dpm: 0x0a95, gy: 2043, gm: 12, gd: 3),
+  HijriYearRecord(hy: 1467, dpm: 0x052d, gy: 2044, gm: 11, gd: 21),
+  HijriYearRecord(hy: 1468, dpm: 0x0aad, gy: 2045, gm: 11, gd: 10),
+  HijriYearRecord(hy: 1469, dpm: 0x036c, gy: 2046, gm: 10, gd: 31),
+  HijriYearRecord(hy: 1470, dpm: 0x0759, gy: 2047, gm: 10, gd: 20),
+  HijriYearRecord(hy: 1471, dpm: 0x06d2, gy: 2048, gm: 10, gd: 9),
+  HijriYearRecord(hy: 1472, dpm: 0x0695, gy: 2049, gm: 9, gd: 28),
+  HijriYearRecord(hy: 1473, dpm: 0x052d, gy: 2050, gm: 9, gd: 17),
+  HijriYearRecord(hy: 1474, dpm: 0x0a5b, gy: 2051, gm: 9, gd: 6),
+  HijriYearRecord(hy: 1475, dpm: 0x04ba, gy: 2052, gm: 8, gd: 26),
+  HijriYearRecord(hy: 1476, dpm: 0x09ba, gy: 2053, gm: 8, gd: 15),
+  HijriYearRecord(hy: 1477, dpm: 0x03b4, gy: 2054, gm: 8, gd: 5),
+  HijriYearRecord(hy: 1478, dpm: 0x0b69, gy: 2055, gm: 7, gd: 25),
+  HijriYearRecord(hy: 1479, dpm: 0x0b52, gy: 2056, gm: 7, gd: 14),
+  HijriYearRecord(hy: 1480, dpm: 0x0aa6, gy: 2057, gm: 7, gd: 3),
+  HijriYearRecord(hy: 1481, dpm: 0x04b6, gy: 2058, gm: 6, gd: 22),
+  HijriYearRecord(hy: 1482, dpm: 0x096d, gy: 2059, gm: 6, gd: 11),
+  HijriYearRecord(hy: 1483, dpm: 0x02ec, gy: 2060, gm: 5, gd: 31),
+  HijriYearRecord(hy: 1484, dpm: 0x06d9, gy: 2061, gm: 5, gd: 20),
+  HijriYearRecord(hy: 1485, dpm: 0x0eb2, gy: 2062, gm: 5, gd: 10),
+  HijriYearRecord(hy: 1486, dpm: 0x0d54, gy: 2063, gm: 4, gd: 30),
+  HijriYearRecord(hy: 1487, dpm: 0x0d2a, gy: 2064, gm: 4, gd: 18),
+  HijriYearRecord(hy: 1488, dpm: 0x0a56, gy: 2065, gm: 4, gd: 7),
+  HijriYearRecord(hy: 1489, dpm: 0x04ae, gy: 2066, gm: 3, gd: 27),
+  HijriYearRecord(hy: 1490, dpm: 0x096d, gy: 2067, gm: 3, gd: 16),
+  HijriYearRecord(hy: 1491, dpm: 0x0d6a, gy: 2068, gm: 3, gd: 5),
+  HijriYearRecord(hy: 1492, dpm: 0x0b54, gy: 2069, gm: 2, gd: 23),
+  HijriYearRecord(hy: 1493, dpm: 0x0b29, gy: 2070, gm: 2, gd: 12),
+  HijriYearRecord(hy: 1494, dpm: 0x0a93, gy: 2071, gm: 2, gd: 1),
+  HijriYearRecord(hy: 1495, dpm: 0x052b, gy: 2072, gm: 1, gd: 21),
+  HijriYearRecord(hy: 1496, dpm: 0x0a57, gy: 2073, gm: 1, gd: 9),
+  HijriYearRecord(hy: 1497, dpm: 0x0536, gy: 2073, gm: 12, gd: 30),
+  HijriYearRecord(hy: 1498, dpm: 0x0ab5, gy: 2074, gm: 12, gd: 19),
+  HijriYearRecord(hy: 1499, dpm: 0x06aa, gy: 2075, gm: 12, gd: 9),
+  HijriYearRecord(hy: 1500, dpm: 0x0e93, gy: 2076, gm: 11, gd: 27),
+  HijriYearRecord(hy: 1501, dpm: 0, gy: 2077, gm: 11, gd: 17),
+];
diff --git a/lib/src/engines/fcna.dart b/lib/src/engines/fcna.dart
new file mode 100644
index 0000000..9956336
--- /dev/null
+++ b/lib/src/engines/fcna.dart
@@ -0,0 +1,313 @@
+// FCNA engine: Fiqh Council of North America / ISNA calendar.
+//
+// The FCNA criterion: if the new moon conjunction occurs before 12:00 noon UTC
+// on day D, the new Hijri month begins at midnight starting day D+1. If at or
+// after 12:00 UTC, the month begins at midnight starting day D+2.
+//
+// New moon times come from Jean Meeus, Astronomical Algorithms (2nd ed.),
+// Chapter 49, accurate to within a few minutes for 1000-3000 CE.
+
+import 'dart:math' as math;
+
+import '../constants.dart';
+import '../data.dart';
+import '../types.dart';
+
+// ---- Constants ----
+
+const double _synodic = 29.530588861; // Mean synodic month (days)
+const double _jde0 =
+    2451550.09766; // Meeus k=0 (2nd ed. Ch.49: 2451550.09765; 0.864 s diff)
+const double _jdeUnix = 2440587.5; // JDE of Unix epoch 1970-01-01 00:00 UTC
+const double _toRad = math.pi / 180;
+
+// Approximate k index of 1 Muharram 1 AH in Meeus numbering.
+// Islamic epoch JDE ~1948438.5 -> k ~= (1948438.5 - _jde0) / _synodic ~= -17037.
+const int _kEpoch = -17037;
+
+// ---- Meeus Chapter 49: corrected new moon JDE ----
+
+double _newMoonJDE(double k) {
+  final t = k / 1236.85;
+  final t2 = t * t;
+  final t3 = t2 * t;
+  final t4 = t3 * t;
+
+  double jde =
+      _jde0 +
+      _synodic * k +
+      0.00015437 * t2 -
+      0.00000015 * t3 +
+      0.00000000073 * t4;
+
+  final m = (2.5534 + 29.1053567 * k - 0.0000014 * t2 - 0.00000011 * t3) % 360;
+
+  final mprime =
+      (201.5643 +
+          385.81693528 * k +
+          0.0107582 * t2 +
+          0.00001238 * t3 -
+          0.000000058 * t4) %
+      360;
+
+  final f =
+      (160.7108 +
+          390.67050284 * k -
+          0.0016118 * t2 -
+          0.00000227 * t3 +
+          0.000000011 * t4) %
+      360;
+
+  final omega =
+      (124.7746 - 1.56375588 * k + 0.0020672 * t2 + 0.00000215 * t3) % 360;
+
+  final e = 1 - 0.002516 * t - 0.0000074 * t2;
+  final e2 = e * e;
+
+  final mRad = m * _toRad;
+  final mpRad = mprime * _toRad;
+  final fRad = f * _toRad;
+  final oRad = omega * _toRad;
+
+  jde +=
+      -0.4072 * math.sin(mpRad) +
+      0.17241 * e * math.sin(mRad) +
+      0.01608 * math.sin(2 * mpRad) +
+      0.01039 * math.sin(2 * fRad) +
+      0.00739 * e * math.sin(mpRad - mRad) -
+      0.00514 * e * math.sin(mpRad + mRad) +
+      0.00208 * e2 * math.sin(2 * mRad) -
+      0.00111 * math.sin(mpRad - 2 * fRad) -
+      0.00057 * math.sin(mpRad + 2 * fRad) +
+      0.00056 * e * math.sin(2 * mpRad + mRad) -
+      0.00042 * math.sin(3 * mpRad) +
+      0.00042 * e * math.sin(mRad + 2 * fRad) +
+      0.00038 * e * math.sin(mRad - 2 * fRad) -
+      0.00024 * e * math.sin(2 * mpRad - mRad) -
+      0.00017 * math.sin(oRad) -
+      0.00007 * math.sin(mpRad + 2 * mRad) +
+      0.00004 * math.sin(2 * mpRad - 2 * fRad) +
+      0.00004 * math.sin(3 * mRad) +
+      0.00003 * math.sin(mpRad + mRad - 2 * fRad) +
+      0.00003 * math.sin(2 * mpRad + 2 * fRad) -
+      0.00003 * math.sin(mpRad + mRad + 2 * fRad) +
+      0.00003 * math.sin(mpRad - mRad + 2 * fRad) -
+      0.00002 * math.sin(mpRad - mRad - 2 * fRad) -
+      0.00002 * math.sin(3 * mpRad + mRad) +
+      0.00002 * math.sin(4 * mpRad);
+
+  final a1 = (299.77 + 0.107408 * k - 0.009173 * t2) * _toRad;
+  final a2 = (251.88 + 0.016321 * k) * _toRad;
+  final a3 = (251.83 + 26.651886 * k) * _toRad;
+  final a4 = (349.42 + 36.412478 * k) * _toRad;
+  final a5 = (84.66 + 18.206239 * k) * _toRad;
+  final a6 = (141.74 + 53.303771 * k) * _toRad;
+  final a7 = (207.14 + 2.453732 * k) * _toRad;
+  final a8 = (154.84 + 7.30686 * k) * _toRad;
+  final a9 = (34.52 + 27.261239 * k) * _toRad;
+  final a10 = (207.19 + 0.121824 * k) * _toRad;
+  final a11 = (291.34 + 1.844379 * k) * _toRad;
+  final a12 = (161.72 + 24.198154 * k) * _toRad;
+  final a13 = (239.56 + 25.513099 * k) * _toRad;
+  final a14 = (331.55 + 3.592518 * k) * _toRad;
+
+  jde +=
+      0.000325 * math.sin(a1) +
+      0.000165 * math.sin(a2) +
+      0.000164 * math.sin(a3) +
+      0.000126 * math.sin(a4) +
+      0.00011 * math.sin(a5) +
+      0.000062 * math.sin(a6) +
+      0.00006 * math.sin(a7) +
+      0.000056 * math.sin(a8) +
+      0.000047 * math.sin(a9) +
+      0.000042 * math.sin(a10) +
+      0.00004 * math.sin(a11) +
+      0.000037 * math.sin(a12) +
+      0.000035 * math.sin(a13) +
+      0.000023 * math.sin(a14);
+
+  return jde;
+}
+
+// ---- JDE / UTC conversion ----
+
+double _jdeToUtcMs(double jde) {
+  return (jde - _jdeUnix) * msPerDay;
+}
+
+double _utcMsToKApprox(double ms) {
+  final jde = ms / msPerDay + _jdeUnix;
+  return (jde - _jde0) / _synodic;
+}
+
+// ---- Find nearest corrected new moon ----
+
+// Searches k0-2 through k0+2 to handle any estimation error.
+double _nearestNewMoonMs(double anchorMs) {
+  final k0 = _utcMsToKApprox(anchorMs).round();
+  double bestMs = 0;
+  double bestDist = double.infinity;
+
+  for (int k = k0 - 2; k <= k0 + 2; k++) {
+    final ms = _jdeToUtcMs(_newMoonJDE(k.toDouble()));
+    final dist = (ms - anchorMs).abs();
+    if (dist < bestDist) {
+      bestDist = dist;
+      bestMs = ms;
+    }
+  }
+
+  return bestMs;
+}
+
+// ---- FCNA criterion ----
+
+// Returns the midnight UTC ms that starts the new FCNA Hijri month.
+double _fcnaCriterionMs(double conjMs) {
+  final midnight = (conjMs / msPerDay).floor() * msPerDay;
+  final noon = midnight + 12 * 3600000;
+  return (conjMs < noon ? midnight + msPerDay : midnight + 2 * msPerDay)
+      .toDouble();
+}
+
+// ---- UAQ anchor ----
+
+// Returns the UTC ms of the UAQ month start for (hy, hm).
+// In-range years (1318-1500 H): binary-search table, sum dpm day counts.
+// Out-of-range years: estimate from Islamic epoch + mean synodic month count.
+double _uaqAnchorMs(int hy, int hm) {
+  int lo = 0;
+  int hi = hDatesTable.length - 1;
+  int found = -1;
+
+  while (lo <= hi) {
+    final mid = (lo + hi) >>> 1;
+    final midHy = hDatesTable[mid].hy;
+    if (midHy == hy) {
+      found = mid;
+      break;
+    } else if (midHy < hy) {
+      lo = mid + 1;
+    } else {
+      hi = mid - 1;
+    }
+  }
+
+  if (found != -1 && hDatesTable[found].dpm != 0) {
+    final r = hDatesTable[found];
+    int days = 0;
+    for (int i = 0; i < hm - 1; i++) {
+      days += (r.dpm >> i) & 1 == 1 ? 30 : 29;
+    }
+    return (DateTime.utc(r.gy, r.gm, r.gd).millisecondsSinceEpoch +
+            days * msPerDay)
+        .toDouble();
+  }
+
+  final monthsFromEpoch = (hy - 1) * monthsPerYear + (hm - 1);
+  final kApprox = _kEpoch + monthsFromEpoch;
+  return _jdeToUtcMs(_newMoonJDE(kApprox.toDouble()));
+}
+
+// ---- FCNA month start ----
+
+double _fcnaMonthStartMs(int hy, int hm) {
+  final anchor = _uaqAnchorMs(hy, hm);
+  final conjMs = _nearestNewMoonMs(anchor);
+  return _fcnaCriterionMs(conjMs);
+}
+
+// ---- FCNA month length ----
+
+int _fcnaDaysInMonth(int hy, int hm) {
+  if (hm < 1 || hm > monthsPerYear) {
+    throw RangeError('month must be 1-12, got $hm');
+  }
+  final thisStart = _fcnaMonthStartMs(hy, hm);
+  final nextHy = hm < monthsPerYear ? hy : hy + 1;
+  final nextHm = hm < monthsPerYear ? hm + 1 : 1;
+  final nextStart = _fcnaMonthStartMs(nextHy, nextHm);
+  return ((nextStart - thisStart) / msPerDay).round();
+}
+
+// ---- FCNA Gregorian -> Hijri ----
+
+HijriDate? _fcnaToHijri(DateTime date) {
+  // FCNA criterion is UTC-based, so UTC date components ensure correct round-trips.
+  final inputMs =
+      DateTime.utc(
+        date.year,
+        date.month,
+        date.day,
+      ).millisecondsSinceEpoch.toDouble();
+
+  final kApprox = _utcMsToKApprox(inputMs - 15 * msPerDay);
+  final k0 = kApprox.floor();
+
+  for (int ki = k0 - 1; ki <= k0 + 1; ki++) {
+    final conjMs = _jdeToUtcMs(_newMoonJDE(ki.toDouble()));
+    final monthStart = _fcnaCriterionMs(conjMs);
+
+    if (monthStart > inputMs) continue;
+
+    final nextConjMs = _jdeToUtcMs(_newMoonJDE((ki + 1).toDouble()));
+    final nextMonthStart = _fcnaCriterionMs(nextConjMs);
+
+    if (inputMs < nextMonthStart) {
+      final monthsFromEpoch = ki - _kEpoch;
+      int hy = monthsFromEpoch ~/ monthsPerYear + 1;
+      int hm = (monthsFromEpoch % monthsPerYear) + 1;
+      if (hm <= 0) {
+        hm += monthsPerYear;
+        hy--;
+      }
+      if (hy < 1) return null;
+
+      final hd = ((inputMs - monthStart) / msPerDay).round() + 1;
+      return HijriDate(hy: hy, hm: hm, hd: hd);
+    }
+  }
+
+  return null;
+}
+
+// ---- FCNA Hijri -> Gregorian ----
+
+DateTime? _fcnaToGregorian(int hy, int hm, int hd) {
+  if (hy < 1 || hm < 1 || hm > monthsPerYear || hd < 1) return null;
+  final days = _fcnaDaysInMonth(hy, hm);
+  if (hd > days) return null;
+  final startMs = _fcnaMonthStartMs(hy, hm);
+  return DateTime.fromMillisecondsSinceEpoch(
+    (startMs + (hd - 1) * msPerDay).round(),
+    isUtc: true,
+  );
+}
+
+// ---- FCNA validation ----
+
+bool _fcnaIsValid(int hy, int hm, int hd) {
+  if (hy < 1 || hm < 1 || hm > monthsPerYear || hd < 1) return false;
+  return hd <= _fcnaDaysInMonth(hy, hm);
+}
+
+/// The FCNA (Fiqh Council of North America) calendar engine.
+final CalendarEngine fcnaEngine = _FcnaEngine();
+
+class _FcnaEngine extends CalendarEngine {
+  @override
+  String get id => 'fcna';
+
+  @override
+  HijriDate? toHijri(DateTime date) => _fcnaToHijri(date);
+
+  @override
+  DateTime? toGregorian(int hy, int hm, int hd) => _fcnaToGregorian(hy, hm, hd);
+
+  @override
+  bool isValid(int hy, int hm, int hd) => _fcnaIsValid(hy, hm, hd);
+
+  @override
+  int daysInMonth(int hy, int hm) => _fcnaDaysInMonth(hy, hm);
+}
diff --git a/lib/src/engines/uaq.dart b/lib/src/engines/uaq.dart
new file mode 100644
index 0000000..1fe7a74
--- /dev/null
+++ b/lib/src/engines/uaq.dart
@@ -0,0 +1,141 @@
+// UAQ engine: Umm al-Qura calendar (official Saudi Arabian Islamic calendar).
+//
+// Conversions are table-driven. The reference table covers Hijri years 1318-1500
+// (Gregorian 1900-2076). Each entry records the Gregorian date of 1 Muharram and
+// a 12-bit days-per-month bitmask. Dates outside that window return null.
+
+import '../constants.dart';
+import '../data.dart';
+import '../types.dart';
+
+/// Binary search for a Hijri year entry in the UAQ table.
+///
+/// Returns the entry whose [hy] matches exactly, or null if the year is not
+/// present in the table. The table covers Hijri years 1318 through 1501
+/// (the final entry is a sentinel with dpm == 0).
+HijriYearRecord? _findYearEntry(int hy) {
+  int lo = 0;
+  int hi = hDatesTable.length - 1;
+
+  while (lo <= hi) {
+    final mid = (lo + hi) >>> 1;
+    final midHy = hDatesTable[mid].hy;
+    if (midHy == hy) return hDatesTable[mid];
+    if (midHy < hy) {
+      lo = mid + 1;
+    } else {
+      hi = mid - 1;
+    }
+  }
+  return null;
+}
+
+/// Compute UTC milliseconds since epoch for a Gregorian date.
+int _dateUtcMs(int year, int month, int day) {
+  return DateTime.utc(year, month, day).millisecondsSinceEpoch;
+}
+
+HijriDate? _uaqToHijri(DateTime date) {
+  final inputUtc = _dateUtcMs(date.year, date.month, date.day);
+
+  // Binary search: find the last table entry whose Gregorian start date <= input.
+  int lo = 0;
+  int hi = hDatesTable.length - 1;
+  int found = -1;
+
+  while (lo <= hi) {
+    final mid = (lo + hi) >>> 1;
+    final entry = hDatesTable[mid];
+    final entryUtc = _dateUtcMs(entry.gy, entry.gm, entry.gd);
+
+    if (entryUtc <= inputUtc) {
+      found = mid;
+      lo = mid + 1;
+    } else {
+      hi = mid - 1;
+    }
+  }
+
+  // dpm == 0 is the sentinel entry (hy 1501) marking the upper bound.
+  if (found == -1 || hDatesTable[found].dpm == 0) return null;
+
+  final record = hDatesTable[found];
+  final startUtc = _dateUtcMs(record.gy, record.gm, record.gd);
+  int remaining = ((inputUtc - startUtc) / msPerDay).round();
+  int hijriMonth = 0;
+
+  for (int i = 0; i < monthsPerYear; i++) {
+    final dim = (record.dpm >> i) & 1 == 1 ? 30 : 29;
+    if (remaining < dim) {
+      hijriMonth = i + 1;
+      break;
+    }
+    remaining -= dim;
+  }
+
+  if (hijriMonth == 0) return null;
+
+  return HijriDate(hy: record.hy, hm: hijriMonth, hd: remaining + 1);
+}
+
+DateTime? _uaqToGregorian(int hy, int hm, int hd) {
+  if (!_uaqIsValid(hy, hm, hd)) return null;
+
+  final record = _findYearEntry(hy);
+  if (record == null) return null;
+
+  int totalDays = 0;
+  for (int i = 0; i < hm - 1; i++) {
+    totalDays += (record.dpm >> i) & 1 == 1 ? 30 : 29;
+  }
+  totalDays += hd - 1;
+
+  return DateTime.fromMillisecondsSinceEpoch(
+    _dateUtcMs(record.gy, record.gm, record.gd) + totalDays * msPerDay,
+    isUtc: true,
+  );
+}
+
+bool _uaqIsValid(int hy, int hm, int hd) {
+  if (hm < 1 || hm > monthsPerYear || hd < 1) return false;
+
+  final record = _findYearEntry(hy);
+  if (record == null || record.dpm == 0) return false;
+
+  final dim = (record.dpm >> (hm - 1)) & 1 == 1 ? 30 : 29;
+  return hd <= dim;
+}
+
+int _uaqDaysInMonth(int hy, int hm) {
+  if (hm < 1 || hm > monthsPerYear) {
+    throw RangeError('month must be 1-12, got $hm');
+  }
+
+  final record = _findYearEntry(hy);
+  if (record == null || record.dpm == 0) {
+    throw RangeError(
+      'Hijri year $hy is outside the UAQ table range (1318-1500).',
+    );
+  }
+  return (record.dpm >> (hm - 1)) & 1 == 1 ? 30 : 29;
+}
+
+/// The Umm al-Qura calendar engine.
+final CalendarEngine uaqEngine = _UaqEngine();
+
+class _UaqEngine extends CalendarEngine {
+  @override
+  String get id => 'uaq';
+
+  @override
+  HijriDate? toHijri(DateTime date) => _uaqToHijri(date);
+
+  @override
+  DateTime? toGregorian(int hy, int hm, int hd) => _uaqToGregorian(hy, hm, hd);
+
+  @override
+  bool isValid(int hy, int hm, int hd) => _uaqIsValid(hy, hm, hd);
+
+  @override
+  int daysInMonth(int hy, int hm) => _uaqDaysInMonth(hy, hm);
+}
diff --git a/lib/src/hijri_core_api.dart b/lib/src/hijri_core_api.dart
new file mode 100644
index 0000000..a0f4c48
--- /dev/null
+++ b/lib/src/hijri_core_api.dart
@@ -0,0 +1,51 @@
+import 'engines/fcna.dart';
+import 'engines/uaq.dart';
+import 'registry.dart';
+import 'types.dart';
+
+// Register built-in engines at first access.
+bool _registered = false;
+
+void _ensureRegistered() {
+  if (!_registered) {
+    registerCalendar('uaq', uaqEngine);
+    registerCalendar('fcna', fcnaEngine);
+    _registered = true;
+  }
+}
+
+/// Convert a Gregorian [DateTime] to a Hijri date.
+///
+/// Uses the UAQ (Umm al-Qura) calendar by default. Pass
+/// `ConversionOptions(calendar: 'fcna')` or any registered calendar name
+/// via [options] to use a different engine.
+///
+/// Returns null if the date is out of range for the selected engine.
+HijriDate? toHijri(DateTime date, {ConversionOptions? options}) {
+  _ensureRegistered();
+  return getCalendar(options?.calendar ?? 'uaq').toHijri(date);
+}
+
+/// Convert a Hijri date to a Gregorian [DateTime] (UTC).
+///
+/// Uses the UAQ calendar by default.
+///
+/// Returns null if the input is invalid or out of range.
+DateTime? toGregorian(int hy, int hm, int hd, {ConversionOptions? options}) {
+  _ensureRegistered();
+  return getCalendar(options?.calendar ?? 'uaq').toGregorian(hy, hm, hd);
+}
+
+/// Check whether a Hijri date is valid for the given calendar engine.
+bool isValidHijriDate(int hy, int hm, int hd, {ConversionOptions? options}) {
+  _ensureRegistered();
+  return getCalendar(options?.calendar ?? 'uaq').isValid(hy, hm, hd);
+}
+
+/// Return the number of days in a given Hijri month (29 or 30).
+///
+/// Throws [RangeError] if the month or year is out of range.
+int daysInHijriMonth(int hy, int hm, {ConversionOptions? options}) {
+  _ensureRegistered();
+  return getCalendar(options?.calendar ?? 'uaq').daysInMonth(hy, hm);
+}
diff --git a/lib/src/names/months.dart b/lib/src/names/months.dart
new file mode 100644
index 0000000..bc983b4
--- /dev/null
+++ b/lib/src/names/months.dart
@@ -0,0 +1,48 @@
+/// Hijri month names in long form.
+/// Index 0 = Muharram (month 1), index 11 = Dhul Hijjah (month 12).
+const List<String> hmLong = [
+  'Muharram', // 1
+  'Safar', // 2
+  "Rabi'l Awwal", // 3
+  "Rabi'l Thani", // 4
+  'Jumadal Awwal', // 5
+  'Jumadal Thani', // 6
+  'Rajab', // 7
+  "Sha'ban", // 8
+  'Ramadan', // 9
+  'Shawwal', // 10
+  "Dhul Qi'dah", // 11
+  'Dhul Hijjah', // 12
+];
+
+/// Hijri month names in medium form.
+const List<String> hmMedium = [
+  'Muharram',
+  'Safar',
+  'Rabi1',
+  'Rabi2',
+  'Jumada1',
+  'Jumada2',
+  'Rajab',
+  'Shaban',
+  'Ramadan',
+  'Shawwal',
+  'Dhul-Qidah',
+  'Dhul-Hijjah',
+];
+
+/// Hijri month names in short form.
+const List<String> hmShort = [
+  'Muh',
+  'Saf',
+  'Ra1',
+  'Ra2',
+  'Ju1',
+  'Ju2',
+  'Raj',
+  'Shb',
+  'Ram',
+  'Shw',
+  'DhQ',
+  'DhH',
+];
diff --git a/lib/src/names/weekdays.dart b/lib/src/names/weekdays.dart
new file mode 100644
index 0000000..fcce12e
--- /dev/null
+++ b/lib/src/names/weekdays.dart
@@ -0,0 +1,25 @@
+/// Hijri weekday names in long form.
+/// Index 0 = Sunday, index 6 = Saturday (matching DateTime.weekday % 7).
+const List<String> hwLong = [
+  'Yawm al-Ahad', // Sunday
+  'Yawm al-Ithnayn', // Monday
+  "Yawm ath-Thulatha'", // Tuesday
+  "Yawm al-Arba`a'", // Wednesday
+  'Yawm al-Khamis', // Thursday
+  'Yawm al-Jum`a', // Friday
+  'Yawm as-Sabt', // Saturday
+];
+
+/// Hijri weekday names in short form.
+const List<String> hwShort = [
+  'Ahad', // Sunday
+  'Ithn', // Monday
+  'Thul', // Tuesday
+  'Arba', // Wednesday
+  'Kham', // Thursday
+  'Jum`a', // Friday
+  'Sabt', // Saturday
+];
+
+/// Numeric weekday representation: 1 = Sunday, 7 = Saturday.
+const List<int> hwNumeric = [1, 2, 3, 4, 5, 6, 7];
diff --git a/lib/src/registry.dart b/lib/src/registry.dart
new file mode 100644
index 0000000..8cdb524
--- /dev/null
+++ b/lib/src/registry.dart
@@ -0,0 +1,32 @@
+import 'types.dart';
+
+final Map<String, CalendarEngine> _engines = {};
+
+/// Register a calendar engine under the given name.
+///
+/// Once registered, the engine can be selected via [ConversionOptions.calendar]
+/// in any conversion function or retrieved directly with [getCalendar].
+void registerCalendar(String name, CalendarEngine engine) {
+  _engines[name] = engine;
+}
+
+/// Retrieve a registered calendar engine by name.
+///
+/// Throws [StateError] if no engine is registered under that name.
+CalendarEngine getCalendar(String name) {
+  final engine = _engines[name];
+  if (engine == null) {
+    final available = listCalendars().join(', ');
+    throw StateError(
+      'Unknown Hijri calendar: "$name". '
+      'Available: $available. '
+      'Register custom calendars with registerCalendar().',
+    );
+  }
+  return engine;
+}
+
+/// List the names of all registered calendar engines.
+List<String> listCalendars() {
+  return _engines.keys.toList();
+}
diff --git a/lib/src/types.dart b/lib/src/types.dart
new file mode 100644
index 0000000..a9d91a1
--- /dev/null
+++ b/lib/src/types.dart
@@ -0,0 +1,80 @@
+/// A Hijri calendar date with year, month, and day.
+class HijriDate {
+  /// Hijri year.
+  final int hy;
+
+  /// Hijri month (1-12).
+  final int hm;
+
+  /// Hijri day (1-30).
+  final int hd;
+
+  const HijriDate({required this.hy, required this.hm, required this.hd});
+
+  @override
+  bool operator ==(Object other) =>
+      other is HijriDate && hy == other.hy && hm == other.hm && hd == other.hd;
+
+  @override
+  int get hashCode => Object.hash(hy, hm, hd);
+
+  @override
+  String toString() => 'HijriDate(hy: $hy, hm: $hm, hd: $hd)';
+}
+
+/// A row in the Umm al-Qura reference table.
+class HijriYearRecord {
+  /// Hijri year.
+  final int hy;
+
+  /// Days-per-month bitmask. Bit i (0-indexed) corresponds to month i+1:
+  /// 1 = 30 days, 0 = 29 days.
+  final int dpm;
+
+  /// Gregorian year of 1 Muharram.
+  final int gy;
+
+  /// Gregorian month of 1 Muharram (1-based).
+  final int gm;
+
+  /// Gregorian day of 1 Muharram.
+  final int gd;
+
+  const HijriYearRecord({
+    required this.hy,
+    required this.dpm,
+    required this.gy,
+    required this.gm,
+    required this.gd,
+  });
+}
+
+/// Any calendar engine must implement this interface.
+abstract class CalendarEngine {
+  /// Unique identifier for this engine (e.g. 'uaq', 'fcna').
+  String get id;
+
+  /// Convert a Gregorian [DateTime] (UTC) to a Hijri date.
+  /// Returns null for out-of-range input.
+  /// Throws [ArgumentError] for invalid input.
+  HijriDate? toHijri(DateTime date);
+
+  /// Convert a Hijri date to a Gregorian [DateTime] (UTC).
+  /// Returns null for invalid or out-of-range input.
+  DateTime? toGregorian(int hy, int hm, int hd);
+
+  /// Check whether a Hijri date is valid for this engine.
+  bool isValid(int hy, int hm, int hd);
+
+  /// Return the number of days in a given Hijri month (29 or 30).
+  /// Throws [RangeError] if the month or year is out of range.
+  int daysInMonth(int hy, int hm);
+}
+
+/// Options for selecting which calendar engine to use.
+class ConversionOptions {
+  /// Calendar engine name. Defaults to 'uaq'.
+  final String? calendar;
+
+  const ConversionOptions({this.calendar});
+}
diff --git a/pubspec.yaml b/pubspec.yaml
new file mode 100644
index 0000000..15a7ca4
--- /dev/null
+++ b/pubspec.yaml
@@ -0,0 +1,20 @@
+name: hijri_core
+description: >
+  Hijri/Gregorian calendar conversion for Dart and Flutter. Pluggable engine
+  system with built-in Umm al-Qura and FCNA calendars. Zero dependencies.
+version: 1.0.0
+repository: https://github.com/acamarata/hijri-core-dart
+issue_tracker: https://github.com/acamarata/hijri-core-dart/issues
+topics:
+  - hijri
+  - islamic
+  - calendar
+  - gregorian
+  - umm-al-qura
+
+environment:
+  sdk: ^3.7.0
+
+dev_dependencies:
+  lints: ^5.0.0
+  test: ^1.25.8
diff --git a/test/hijri_core_test.dart b/test/hijri_core_test.dart
new file mode 100644
index 0000000..606a04c
--- /dev/null
+++ b/test/hijri_core_test.dart
@@ -0,0 +1,351 @@
+import 'package:hijri_core/hijri_core.dart';
+import 'package:test/test.dart';
+
+void main() {
+  // ---- Exports exist ----
+
+  group('exports', () {
+    test('toHijri is callable', () {
+      expect(toHijri, isA<Function>());
+    });
+    test('toGregorian is callable', () {
+      expect(toGregorian, isA<Function>());
+    });
+    test('isValidHijriDate is callable', () {
+      expect(isValidHijriDate, isA<Function>());
+    });
+    test('daysInHijriMonth is callable', () {
+      expect(daysInHijriMonth, isA<Function>());
+    });
+    test('registerCalendar is callable', () {
+      expect(registerCalendar, isA<Function>());
+    });
+    test('getCalendar is callable', () {
+      expect(getCalendar, isA<Function>());
+    });
+    test('listCalendars is callable', () {
+      expect(listCalendars, isA<Function>());
+    });
+    test('hDatesTable has > 180 entries', () {
+      expect(hDatesTable.length, greaterThan(180));
+    });
+    test('hmLong has 12 entries', () {
+      expect(hmLong.length, equals(12));
+    });
+    test('hmMedium has 12 entries', () {
+      expect(hmMedium.length, equals(12));
+    });
+    test('hmShort has 12 entries', () {
+      expect(hmShort.length, equals(12));
+    });
+    test('hwLong has 7 entries', () {
+      expect(hwLong.length, equals(7));
+    });
+    test('hwShort has 7 entries', () {
+      expect(hwShort.length, equals(7));
+    });
+    test('hwNumeric has 7 entries [1..7]', () {
+      expect(hwNumeric, equals([1, 2, 3, 4, 5, 6, 7]));
+    });
+  });
+
+  // ---- UAQ toGregorian ----
+
+  group('UAQ toGregorian', () {
+    test('1444/9/1 = 2023-03-23', () {
+      final d = toGregorian(1444, 9, 1);
+      expect(d, isNotNull);
+      expect(d!.toIso8601String().substring(0, 10), equals('2023-03-23'));
+    });
+    test('1446/9/1 = 2025-03-01', () {
+      final d = toGregorian(1446, 9, 1);
+      expect(d, isNotNull);
+      expect(d!.toIso8601String().substring(0, 10), equals('2025-03-01'));
+    });
+    test('1446/10/1 = 2025-03-30', () {
+      final d = toGregorian(1446, 10, 1);
+      expect(d, isNotNull);
+      expect(d!.toIso8601String().substring(0, 10), equals('2025-03-30'));
+    });
+    test('1318/1/1 = 1900-04-30', () {
+      final d = toGregorian(1318, 1, 1);
+      expect(d, isNotNull);
+      expect(d!.toIso8601String().substring(0, 10), equals('1900-04-30'));
+    });
+  });
+
+  // ---- UAQ toHijri ----
+
+  group('UAQ toHijri', () {
+    test('2023-03-23 = 1444/9/1', () {
+      final h = toHijri(DateTime.utc(2023, 3, 23));
+      expect(h, isNotNull);
+      expect(h!.hy, equals(1444));
+      expect(h.hm, equals(9));
+      expect(h.hd, equals(1));
+    });
+    test('2025-03-01 = 1446/9/1', () {
+      final h = toHijri(DateTime.utc(2025, 3, 1));
+      expect(h, isNotNull);
+      expect(h!.hy, equals(1446));
+      expect(h.hm, equals(9));
+      expect(h.hd, equals(1));
+    });
+  });
+
+  // ---- UAQ isValid ----
+
+  group('UAQ isValid', () {
+    test('1444/9/1 = true', () {
+      expect(isValidHijriDate(1444, 9, 1), isTrue);
+    });
+    test('1317/1/1 = false (before table)', () {
+      expect(isValidHijriDate(1317, 1, 1), isFalse);
+    });
+    test('1501/1/1 = false (sentinel)', () {
+      expect(isValidHijriDate(1501, 1, 1), isFalse);
+    });
+    test('month 0 = false', () {
+      expect(isValidHijriDate(1444, 0, 1), isFalse);
+    });
+    test('month 13 = false', () {
+      expect(isValidHijriDate(1444, 13, 1), isFalse);
+    });
+  });
+
+  // ---- UAQ daysInMonth ----
+
+  group('UAQ daysInMonth', () {
+    test('Ramadan 1444 = 29 days', () {
+      expect(daysInHijriMonth(1444, 9), equals(29));
+    });
+    test('throws for month 0', () {
+      expect(() => daysInHijriMonth(1444, 0), throwsRangeError);
+    });
+    test('throws for month 13', () {
+      expect(() => daysInHijriMonth(1444, 13), throwsRangeError);
+    });
+  });
+
+  // ---- FCNA toGregorian ----
+
+  group('FCNA toGregorian', () {
+    test('1446/9/1 = 2025-03-01', () {
+      final d = toGregorian(
+        1446,
+        9,
+        1,
+        options: const ConversionOptions(calendar: 'fcna'),
+      );
+      expect(d, isNotNull);
+      expect(d!.toIso8601String().substring(0, 10), equals('2025-03-01'));
+    });
+    test('1446/10/1 = 2025-03-30', () {
+      final d = toGregorian(
+        1446,
+        10,
+        1,
+        options: const ConversionOptions(calendar: 'fcna'),
+      );
+      expect(d, isNotNull);
+      expect(d!.toIso8601String().substring(0, 10), equals('2025-03-30'));
+    });
+  });
+
+  // ---- FCNA toHijri ----
+
+  group('FCNA toHijri', () {
+    test('2025-03-01 = 1446/9/1', () {
+      final h = toHijri(
+        DateTime.utc(2025, 3, 1),
+        options: const ConversionOptions(calendar: 'fcna'),
+      );
+      expect(h, isNotNull);
+      expect(h!.hy, equals(1446));
+      expect(h.hm, equals(9));
+      expect(h.hd, equals(1));
+    });
+  });
+
+  // ---- FCNA round-trips ----
+
+  group('FCNA round-trips', () {
+    test('1446/9/1 toGregorian->toHijri', () {
+      final greg = toGregorian(
+        1446,
+        9,
+        1,
+        options: const ConversionOptions(calendar: 'fcna'),
+      );
+      expect(greg, isNotNull);
+      final hijri = toHijri(
+        greg!,
+        options: const ConversionOptions(calendar: 'fcna'),
+      );
+      expect(hijri, isNotNull);
+      expect(hijri!.hy, equals(1446));
+      expect(hijri.hm, equals(9));
+      expect(hijri.hd, equals(1));
+    });
+    test('1446/10/15 toGregorian->toHijri', () {
+      final greg = toGregorian(
+        1446,
+        10,
+        15,
+        options: const ConversionOptions(calendar: 'fcna'),
+      );
+      expect(greg, isNotNull);
+      final hijri = toHijri(
+        greg!,
+        options: const ConversionOptions(calendar: 'fcna'),
+      );
+      expect(hijri, isNotNull);
+      expect(hijri!.hy, equals(1446));
+      expect(hijri.hm, equals(10));
+      expect(hijri.hd, equals(15));
+    });
+  });
+
+  // ---- FCNA isValid ----
+
+  group('FCNA isValid', () {
+    test('1/1/1 = true', () {
+      expect(
+        isValidHijriDate(
+          1,
+          1,
+          1,
+          options: const ConversionOptions(calendar: 'fcna'),
+        ),
+        isTrue,
+      );
+    });
+    test('1600/1/1 = true', () {
+      expect(
+        isValidHijriDate(
+          1600,
+          1,
+          1,
+          options: const ConversionOptions(calendar: 'fcna'),
+        ),
+        isTrue,
+      );
+    });
+    test('0/1/1 = false', () {
+      expect(
+        isValidHijriDate(
+          0,
+          1,
+          1,
+          options: const ConversionOptions(calendar: 'fcna'),
+        ),
+        isFalse,
+      );
+    });
+  });
+
+  // ---- FCNA daysInMonth invalid month ----
+
+  group('FCNA daysInMonth', () {
+    test('throws for month 0', () {
+      expect(
+        () => daysInHijriMonth(
+          1446,
+          0,
+          options: const ConversionOptions(calendar: 'fcna'),
+        ),
+        throwsRangeError,
+      );
+    });
+    test('throws for month 13', () {
+      expect(
+        () => daysInHijriMonth(
+          1446,
+          13,
+          options: const ConversionOptions(calendar: 'fcna'),
+        ),
+        throwsRangeError,
+      );
+    });
+  });
+
+  // ---- Registry ----
+
+  group('registry', () {
+    test('listCalendars includes uaq and fcna', () {
+      final cals = listCalendars();
+      expect(cals, contains('uaq'));
+      expect(cals, contains('fcna'));
+    });
+    test('getCalendar throws for unknown calendar', () {
+      expect(() => getCalendar('nonexistent'), throwsStateError);
+    });
+    test('registerCalendar: custom engine works', () {
+      final mockEngine = _MockEngine();
+      registerCalendar('mock', mockEngine);
+
+      final cals = listCalendars();
+      expect(cals, contains('mock'));
+
+      final h = toHijri(
+        DateTime.utc(2020, 1, 1),
+        options: const ConversionOptions(calendar: 'mock'),
+      );
+      expect(h, isNotNull);
+      expect(h!.hy, equals(999));
+
+      final g = toGregorian(
+        1,
+        1,
+        1,
+        options: const ConversionOptions(calendar: 'mock'),
+      );
+      expect(g, isNotNull);
+      expect(g!.toIso8601String().substring(0, 10), equals('2000-01-01'));
+
+      expect(
+        isValidHijriDate(
+          1,
+          1,
+          1,
+          options: const ConversionOptions(calendar: 'mock'),
+        ),
+        isTrue,
+      );
+      expect(
+        daysInHijriMonth(
+          1,
+          1,
+          options: const ConversionOptions(calendar: 'mock'),
+        ),
+        equals(30),
+      );
+    });
+  });
+
+  // ---- Error cases ----
+
+  group('error cases', () {
+    test('UAQ toGregorian returns null for out-of-range date', () {
+      expect(toGregorian(1317, 1, 1), isNull);
+    });
+  });
+}
+
+class _MockEngine extends CalendarEngine {
+  @override
+  String get id => 'mock';
+
+  @override
+  HijriDate? toHijri(DateTime date) => const HijriDate(hy: 999, hm: 1, hd: 1);
+
+  @override
+  DateTime? toGregorian(int hy, int hm, int hd) => DateTime.utc(2000, 1, 1);
+
+  @override
+  bool isValid(int hy, int hm, int hd) =>
+      hy > 0 && hm >= 1 && hm <= 12 && hd >= 1;
+
+  @override
+  int daysInMonth(int hy, int hm) => 30;
+}