diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000000..7e64d2be1c
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,7 @@
+__pycache__/
+*.py[cod]
+*.egg-info/
+dist/
+build/
+.venv/
+.pytest_cache/
diff --git a/README.md b/README.md
index a1f92f5862..ee4f55622e 100644
--- a/README.md
+++ b/README.md
@@ -1 +1,29 @@
-See you later
\ No newline at end of file
+# Calendar Adapter
+
+This project provides a small Python package that wraps the
+[lunar-python](https://pypi.org/project/lunar-python/) ephemeris in a normalized
+``CalendarAdapter`` facade. The adapter derives BaZi pillars while applying
+solar-term new year (节气换年) rules and handling the ``晚子时`` rollover so that the
+late Zi hour advances the day pillar as expected.
+
+## Getting started
+
+```bash
+python -m venv .venv
+source .venv/bin/activate
+pip install -e .
+pytest
+```
+
+## Example
+
+```python
+from datetime import datetime
+from calendar_adapter import CalendarAdapter
+
+adapter = CalendarAdapter()
+result = adapter.compute_bazi(datetime(2024, 2, 4, 23, 45))
+
+print(result.text)              # e.g. "甲辰癸卯甲子辛亥"
+print(result.metadata.to_dict())  # structured metadata with solar-term context
+```
diff --git a/pyproject.toml b/pyproject.toml
new file mode 100644
index 0000000000..5d32968884
--- /dev/null
+++ b/pyproject.toml
@@ -0,0 +1,24 @@
+[build-system]
+requires = ["setuptools>=68", "wheel"]
+build-backend = "setuptools.build_meta"
+
+[project]
+name = "calendar-adapter"
+version = "0.1.0"
+description = "Calendar adapter that derives BaZi pillars using lunar-python."
+readme = "README.md"
+requires-python = ">=3.10"
+authors = [{ name = "cto.new", email = "engineering@cto.new" }]
+dependencies = [
+    "lunar-python>=1.4,<2.0",
+]
+
+[tool.setuptools]
+package-dir = {"" = "src"}
+
+[tool.setuptools.packages.find]
+where = ["src"]
+
+[tool.pytest.ini_options]
+testpaths = ["tests"]
+addopts = "-q"
diff --git a/src/calendar_adapter/__init__.py b/src/calendar_adapter/__init__.py
new file mode 100644
index 0000000000..1dfaec0cd7
--- /dev/null
+++ b/src/calendar_adapter/__init__.py
@@ -0,0 +1,19 @@
+"""Calendar adapter facade around :mod:`lunar_python` BaZi utilities."""
+
+from .adapter import (
+    BaZiMetadata,
+    BaZiResult,
+    CalendarAdapter,
+    Pillar,
+    SolarTermBoundary,
+    SolarTermInfo,
+)
+
+__all__ = [
+    "BaZiMetadata",
+    "BaZiResult",
+    "CalendarAdapter",
+    "Pillar",
+    "SolarTermBoundary",
+    "SolarTermInfo",
+]
diff --git a/src/calendar_adapter/adapter.py b/src/calendar_adapter/adapter.py
new file mode 100644
index 0000000000..fb78e12634
--- /dev/null
+++ b/src/calendar_adapter/adapter.py
@@ -0,0 +1,261 @@
+from __future__ import annotations
+
+import importlib.metadata
+from dataclasses import dataclass
+from datetime import datetime
+from typing import Dict, Optional
+
+from zoneinfo import ZoneInfo
+
+from lunar_python import JieQi, Lunar, Solar
+
+_DEFAULT_TIMEZONE = ZoneInfo("Asia/Shanghai")
+
+
+@dataclass(frozen=True)
+class Pillar:
+    """Normalized representation of a single Heavenly Stem / Earthly Branch pair."""
+
+    stem: str
+    branch: str
+
+    @property
+    def text(self) -> str:
+        """Concatenated representation of the pillar, e.g. ``癸卯``."""
+
+        return f"{self.stem}{self.branch}"
+
+    def to_dict(self) -> Dict[str, str]:
+        """Serialize the pillar into a dictionary structure."""
+
+        return {
+            "stem": self.stem,
+            "branch": self.branch,
+            "text": self.text,
+        }
+
+
+@dataclass(frozen=True)
+class SolarTermInfo:
+    """Snapshot of a solar term occurrence."""
+
+    name: str
+    moment: datetime
+
+    def to_dict(self) -> Dict[str, str]:
+        return {
+            "name": self.name,
+            "moment": self.moment.isoformat(),
+        }
+
+
+@dataclass(frozen=True)
+class SolarTermBoundary:
+    """Describes how a solar term boundary (e.g. 立春) impacts the calculation."""
+
+    name: str
+    moment: datetime
+    applied_year: int
+    has_passed: bool
+
+    def to_dict(self) -> Dict[str, object]:
+        return {
+            "name": self.name,
+            "moment": self.moment.isoformat(),
+            "applied_year": self.applied_year,
+            "has_passed": self.has_passed,
+        }
+
+
+@dataclass(frozen=True)
+class BaZiMetadata:
+    """Additional context returned alongside the BaZi pillars."""
+
+    solar_moment: datetime
+    timezone: str
+    solar_term_year: int
+    solar_term_year_shifted: bool
+    solar_term_boundary: SolarTermBoundary
+    current_solar_term: Optional[SolarTermInfo]
+    next_solar_term: Optional[SolarTermInfo]
+    late_zi_hour_applied: bool
+    sect: int
+    library: str
+    library_version: str
+    lunar_year: int
+    lunar_month: int
+    lunar_day: int
+    is_leap_month: bool
+
+    def to_dict(self) -> Dict[str, object]:
+        return {
+            "solar": {
+                "moment": self.solar_moment.isoformat(),
+                "timezone": self.timezone,
+            },
+            "lunar": {
+                "year": self.lunar_year,
+                "month": self.lunar_month,
+                "day": self.lunar_day,
+                "is_leap_month": self.is_leap_month,
+            },
+            "solar_term_year": self.solar_term_year,
+            "solar_term_year_shifted": self.solar_term_year_shifted,
+            "solar_terms": {
+                "year_boundary": self.solar_term_boundary.to_dict(),
+                "current": None if self.current_solar_term is None else self.current_solar_term.to_dict(),
+                "next": None if self.next_solar_term is None else self.next_solar_term.to_dict(),
+            },
+            "late_zi_hour_applied": self.late_zi_hour_applied,
+            "sect": self.sect,
+            "source": {
+                "library": self.library,
+                "version": self.library_version,
+            },
+        }
+
+
+@dataclass(frozen=True)
+class BaZiResult:
+    """Container for the computed BaZi pillars and contextual metadata."""
+
+    pillars: Dict[str, Pillar]
+    metadata: BaZiMetadata
+
+    @property
+    def text(self) -> str:
+        """Return the canonical four-pillar string (year→hour)."""
+
+        order = ("year", "month", "day", "hour")
+        return "".join(self.pillars[key].text for key in order if key in self.pillars)
+
+    def to_dict(self) -> Dict[str, object]:
+        """Serialize the result to a JSON-friendly structure."""
+
+        return {
+            "pillars": {key: pillar.to_dict() for key, pillar in self.pillars.items()},
+            "metadata": self.metadata.to_dict(),
+            "text": self.text,
+        }
+
+
+class CalendarAdapter:
+    """High-level facade for producing BaZi pillars via :mod:`lunar_python`."""
+
+    def __init__(self, timezone: str | ZoneInfo = _DEFAULT_TIMEZONE) -> None:
+        if isinstance(timezone, str):
+            timezone = ZoneInfo(timezone)
+        self._timezone: ZoneInfo = timezone
+        self._library_version = importlib.metadata.version("lunar-python")
+
+    def compute_bazi(self, moment: datetime, sect: int = 1) -> BaZiResult:
+        """Compute the BaZi pillars for a moment in time.
+
+        Args:
+            moment: Datetime to evaluate. Naive datetimes are assumed to already be
+                expressed in the adapter's timezone.
+            sect: 八字流派 selection. ``1`` applies the traditional late 子时 rollover
+                that advances the day pillar after midnight, ``2`` keeps the day pillar
+                anchored to the previous day.
+
+        Returns:
+            :class:`BaZiResult` containing normalized pillars and metadata.
+        """
+
+        if sect not in (1, 2):
+            raise ValueError("sect must be either 1 or 2")
+
+        local_moment = self._ensure_timezone(moment)
+        solar = Solar.fromYmdHms(
+            local_moment.year,
+            local_moment.month,
+            local_moment.day,
+            local_moment.hour,
+            local_moment.minute,
+            local_moment.second,
+        )
+        lunar = Lunar.fromSolar(solar)
+        eight_char = lunar.getEightChar()
+        eight_char.setSect(sect)
+
+        pillars = {
+            "year": Pillar(eight_char.getYearGan(), eight_char.getYearZhi()),
+            "month": Pillar(eight_char.getMonthGan(), eight_char.getMonthZhi()),
+            "day": Pillar(eight_char.getDayGan(), eight_char.getDayZhi()),
+            "hour": Pillar(eight_char.getTimeGan(), eight_char.getTimeZhi()),
+        }
+
+        li_chun_solar = lunar.getJieQiTable()["立春"]
+        li_chun_moment = self._solar_to_datetime(li_chun_solar)
+        has_passed_li_chun = local_moment >= li_chun_moment
+        solar_term_year = (
+            li_chun_moment.year if has_passed_li_chun else li_chun_moment.year - 1
+        )
+        solar_term_year_shifted = solar_term_year != local_moment.year
+
+        metadata = BaZiMetadata(
+            solar_moment=local_moment,
+            timezone=self._timezone_key,
+            solar_term_year=solar_term_year,
+            solar_term_year_shifted=solar_term_year_shifted,
+            solar_term_boundary=SolarTermBoundary(
+                name="立春",
+                moment=li_chun_moment,
+                applied_year=solar_term_year,
+                has_passed=has_passed_li_chun,
+            ),
+            current_solar_term=self._jieqi_to_info(lunar.getPrevJie()),
+            next_solar_term=self._jieqi_to_info(lunar.getNextJie()),
+            late_zi_hour_applied=self._is_late_zi_hour(local_moment, sect),
+            sect=sect,
+            library="lunar_python",
+            library_version=self._library_version,
+            lunar_year=lunar.getYear(),
+            lunar_month=abs(lunar.getMonth()),
+            lunar_day=lunar.getDay(),
+            is_leap_month=lunar.getMonth() < 0,
+        )
+
+        return BaZiResult(pillars=pillars, metadata=metadata)
+
+    def _ensure_timezone(self, moment: datetime) -> datetime:
+        if moment.tzinfo is None:
+            return moment.replace(tzinfo=self._timezone)
+        return moment.astimezone(self._timezone)
+
+    @property
+    def _timezone_key(self) -> str:
+        return getattr(self._timezone, "key", str(self._timezone))
+
+    def _solar_to_datetime(self, solar: Solar) -> datetime:
+        return datetime(
+            solar.getYear(),
+            solar.getMonth(),
+            solar.getDay(),
+            solar.getHour(),
+            solar.getMinute(),
+            solar.getSecond(),
+            tzinfo=self._timezone,
+        )
+
+    def _jieqi_to_info(self, jieqi: Optional[JieQi]) -> Optional[SolarTermInfo]:
+        if jieqi is None:
+            return None
+        solar = jieqi.getSolar()
+        return SolarTermInfo(name=jieqi.getName(), moment=self._solar_to_datetime(solar))
+
+    @staticmethod
+    def _is_late_zi_hour(moment: datetime, sect: int) -> bool:
+        """Determine whether the supplied moment falls into the late 子时 window.
+
+        Sect 1 advances the day pillar once the clock passes midnight, while sect 2 keeps
+        the day pillar anchored to the preceding date. We flag the late 子时 window when the
+        hour is between 00:00 and 00:59 inclusive for sect 1, or when the flow switches at
+        23:00 for sect 2.
+        """
+
+        if sect == 1:
+            return moment.hour == 0
+        # Sect 2 keeps the day pillar anchored, so we consider 23:00-23:59 as the rollover
+        # window for completeness.
+        return moment.hour == 23
diff --git a/tests/test_calendar_adapter.py b/tests/test_calendar_adapter.py
new file mode 100644
index 0000000000..9ebc4ccc1b
--- /dev/null
+++ b/tests/test_calendar_adapter.py
@@ -0,0 +1,92 @@
+from __future__ import annotations
+
+from datetime import datetime
+
+from zoneinfo import ZoneInfo
+
+from calendar_adapter import CalendarAdapter
+
+SHANGHAI = ZoneInfo("Asia/Shanghai")
+
+
+def test_solar_term_boundary_switches_year_pillar() -> None:
+    adapter = CalendarAdapter()
+
+    before_li_chun = datetime(2023, 2, 4, 9, 0, tzinfo=SHANGHAI)
+    after_li_chun = datetime(2023, 2, 4, 11, 0, tzinfo=SHANGHAI)
+
+    result_before = adapter.compute_bazi(before_li_chun)
+    result_after = adapter.compute_bazi(after_li_chun)
+
+    assert result_before.pillars["year"].text == "壬寅"
+    assert result_after.pillars["year"].text == "癸卯"
+
+    assert result_before.metadata.solar_term_year == 2022
+    assert result_after.metadata.solar_term_year == 2023
+
+    assert result_before.metadata.solar_term_year_shifted is True
+    assert result_after.metadata.solar_term_year_shifted is False
+
+    boundary = result_before.metadata.solar_term_boundary
+    assert boundary.name == "立春"
+    assert boundary.moment.hour == 10
+    assert boundary.moment.minute == 42
+    assert boundary.applied_year == 2022
+    assert boundary.has_passed is False
+
+    current_term = result_before.metadata.current_solar_term
+    assert current_term is not None
+    assert current_term.name == "小寒"
+
+    next_term = result_before.metadata.next_solar_term
+    assert next_term is not None
+    assert next_term.name == "立春"
+
+    # After crossing the boundary we should be inside 立春 and looking ahead to 惊蛰
+    current_term_after = result_after.metadata.current_solar_term
+    assert current_term_after is not None
+    assert current_term_after.name == "立春"
+    next_term_after = result_after.metadata.next_solar_term
+    assert next_term_after is not None
+    assert next_term_after.name == "惊蛰"
+
+
+def test_late_zi_hour_advances_day_pillar_and_sets_flag() -> None:
+    adapter = CalendarAdapter()
+
+    before_midnight = datetime(2023, 2, 3, 22, 30, tzinfo=SHANGHAI)
+    late_zi = datetime(2023, 2, 4, 0, 30, tzinfo=SHANGHAI)
+    sect_transition = datetime(2023, 2, 3, 23, 30, tzinfo=SHANGHAI)
+
+    before_result = adapter.compute_bazi(before_midnight)
+    late_result = adapter.compute_bazi(late_zi)
+
+    assert before_result.pillars["day"].text == "壬辰"
+    assert late_result.pillars["day"].text == "癸巳"
+
+    assert before_result.metadata.late_zi_hour_applied is False
+    assert late_result.metadata.late_zi_hour_applied is True
+
+    sect_one_result = adapter.compute_bazi(sect_transition, sect=1)
+    sect_two_result = adapter.compute_bazi(sect_transition, sect=2)
+    assert sect_one_result.pillars["day"].text == "癸巳"
+    assert sect_two_result.pillars["day"].text == "壬辰"
+    assert sect_one_result.metadata.late_zi_hour_applied is False
+    assert sect_two_result.metadata.late_zi_hour_applied is True
+
+    assert late_result.metadata.solar_term_year == 2022
+    assert late_result.metadata.solar_term_boundary.has_passed is False
+
+
+def test_serialization_outputs_normalized_payload() -> None:
+    adapter = CalendarAdapter()
+    sample = datetime(2024, 2, 5, 8, 15, tzinfo=SHANGHAI)
+
+    result = adapter.compute_bazi(sample)
+    payload = result.to_dict()
+
+    assert payload["pillars"]["year"]["text"] == result.pillars["year"].text
+    assert payload["metadata"]["solar"]["timezone"] == "Asia/Shanghai"
+    assert payload["metadata"]["solar_terms"]["year_boundary"]["name"] == "立春"
+    assert payload["metadata"]["source"]["library"] == "lunar_python"
+    assert payload["text"] == result.text