diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
new file mode 100644
index 0000000..3c0a2ed
--- /dev/null
+++ b/.github/workflows/ci.yml
@@ -0,0 +1,36 @@
+name: CI
+
+on:
+  push:
+    branches: [main]
+  pull_request:
+    branches: [main]
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        python-version: ["3.10", "3.11", "3.12", "3.13"]
+
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: actions/setup-python@v5
+        with:
+          python-version: ${{ matrix.python-version }}
+
+      - name: Install uv
+        uses: astral-sh/setup-uv@v4
+
+      - name: Install dependencies
+        run: uv sync --group dev
+
+      - name: Lint
+        run: uv run ruff check chatgpt_export_tool tests
+
+      - name: Format check
+        run: uv run ruff format --check chatgpt_export_tool tests
+
+      - name: Test
+        run: uv run pytest --cov=chatgpt_export_tool --cov-report=term-missing
diff --git a/.github/workflows/publish.yml b/.github/workflows/publish.yml
new file mode 100644
index 0000000..d7becf6
--- /dev/null
+++ b/.github/workflows/publish.yml
@@ -0,0 +1,28 @@
+name: Publish to PyPI
+
+on:
+  release:
+    types: [published]
+
+permissions:
+  id-token: write
+
+jobs:
+  publish:
+    runs-on: ubuntu-latest
+    environment: pypi
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: actions/setup-python@v5
+        with:
+          python-version: "3.13"
+
+      - name: Install build tools
+        run: pip install build
+
+      - name: Build package
+        run: python -m build
+
+      - name: Publish to PyPI
+        uses: pypa/gh-action-pypi-publish@release/v1
diff --git a/chatgpt_export_tool/commands/analyze.py b/chatgpt_export_tool/commands/analyze.py
index 28a9590..b2d429c 100644
--- a/chatgpt_export_tool/commands/analyze.py
+++ b/chatgpt_export_tool/commands/analyze.py
@@ -1,7 +1,7 @@
 """Analyze command for chatgpt_export_tool."""
 
 import argparse
-from datetime import datetime
+from datetime import datetime, timezone
 from pathlib import Path
 from typing import Optional
 
@@ -11,6 +11,7 @@
     AnalyzeConfig,
     format_analysis_text,
 )
+from chatgpt_export_tool.core.config.models import DEFAULT_TIME_FORMAT
 from chatgpt_export_tool.core.file_utils import get_file_size
 from chatgpt_export_tool.core.parser import JSONParser
 from chatgpt_export_tool.core.utils import format_size
@@ -54,11 +55,15 @@ def _execute(self) -> None:
         results = parser.analyze(verbose=self.logger.level <= 20)
         results["file_size"] = format_size(file_size)
         results["filepath"] = self.filepath
-        results["analysis_date"] = datetime.now().strftime("%H:%M %d-%m-%Y")
+        time_format = DEFAULT_TIME_FORMAT
+        results["analysis_date"] = datetime.now(tz=timezone.utc).strftime(time_format)
 
         output = format_analysis_text(
             results,
-            AnalyzeConfig(include_fields=self.include_fields),
+            AnalyzeConfig(
+                include_fields=self.include_fields,
+                time_format=time_format,
+            ),
         )
 
         if self.output_file:
diff --git a/chatgpt_export_tool/core/analysis_formatter.py b/chatgpt_export_tool/core/analysis_formatter.py
index 86453eb..5dfd8e4 100644
--- a/chatgpt_export_tool/core/analysis_formatter.py
+++ b/chatgpt_export_tool/core/analysis_formatter.py
@@ -16,9 +16,11 @@ class AnalyzeConfig:
 
     Attributes:
         include_fields: Whether to include field coverage details.
+        time_format: strftime format for date/time display.
     """
 
     include_fields: bool = False
+    time_format: str = "%H:%M %d-%m-%Y"
 
 
 def format_analysis_text(
@@ -56,8 +58,10 @@ def format_analysis_text(
     lines.append(f"Total message nodes in mappings: {results['message_count']:,}")
 
     if results.get("min_date") is not None and results.get("max_date") is not None:
-        lines.append(f"From: {format_timestamp(results['min_date'])}")
-        lines.append(f"To: {format_timestamp(results['max_date'])}")
+        lines.append(
+            f"From: {format_timestamp(results['min_date'], config.time_format)}"
+        )
+        lines.append(f"To: {format_timestamp(results['max_date'], config.time_format)}")
 
     lines.append("")
 
diff --git a/chatgpt_export_tool/core/output/paths.py b/chatgpt_export_tool/core/output/paths.py
index 65e7a0b..1fb5e21 100644
--- a/chatgpt_export_tool/core/output/paths.py
+++ b/chatgpt_export_tool/core/output/paths.py
@@ -94,4 +94,6 @@ def get_unique_filepath(
             candidate = filepath.with_name(f"{filepath.stem}_{suffix}{filepath.suffix}")
             if candidate not in used_paths and not candidate.exists():
                 return candidate
-        raise RuntimeError(f"Could not find unique path for {filepath} after 10000 attempts")
+        raise RuntimeError(
+            f"Could not find unique path for {filepath} after 10000 attempts"
+        )
diff --git a/chatgpt_export_tool/core/transcript/access.py b/chatgpt_export_tool/core/transcript/access.py
index 4b117ab..f375955 100644
--- a/chatgpt_export_tool/core/transcript/access.py
+++ b/chatgpt_export_tool/core/transcript/access.py
@@ -1,6 +1,6 @@
 """Shared read-only helpers for conversation structures."""
 
-from datetime import datetime
+from datetime import datetime, timezone
 from typing import Any, Iterator, Optional
 
 from .thread import (
@@ -86,7 +86,9 @@ def get_date_group_key(conversation: dict[str, Any]) -> Optional[str]:
         return None
 
     try:
-        return datetime.fromtimestamp(float(create_time)).strftime("%Y-%m-%d")
+        return datetime.fromtimestamp(float(create_time), tz=timezone.utc).strftime(
+            "%Y-%m-%d"
+        )
     except (TypeError, ValueError, OSError):
         return None
 
diff --git a/chatgpt_export_tool/core/utils.py b/chatgpt_export_tool/core/utils.py
index 8240089..fd069d0 100644
--- a/chatgpt_export_tool/core/utils.py
+++ b/chatgpt_export_tool/core/utils.py
@@ -1,6 +1,6 @@
 """Small shared formatting helpers."""
 
-from datetime import datetime
+from datetime import datetime, timezone
 
 
 def format_size(size_bytes: int) -> str:
@@ -21,14 +21,14 @@ def format_size(size_bytes: int) -> str:
 
 
 def format_timestamp(timestamp: float, time_format: str = "%H:%M %d-%m-%Y") -> str:
-    """Format a Unix timestamp to human-readable date string.
+    """Format a Unix timestamp to a UTC date string.
 
     Args:
         timestamp: Unix timestamp (seconds since epoch). May be float, int, or Decimal.
+        time_format: strftime format string.
 
     Returns:
-        Formatted date string.
+        Formatted UTC date string.
     """
-    # Handle Decimal values from JSON parser
-    dt = datetime.fromtimestamp(float(timestamp))
+    dt = datetime.fromtimestamp(float(timestamp), tz=timezone.utc)
     return dt.strftime(time_format)