diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..3feb78a
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1 @@
+*.egg-info/
diff --git a/pyproject.toml b/pyproject.toml
index ee17f34..7c99962 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -7,7 +7,10 @@ requires-python = ">=3.11"
 dependencies = []
 
 [project.optional-dependencies]
-dev = ["pytest>=8.0"]
+dev = [
+  "pytest>=8.0",
+  "matplotlib>=3.8",
+]
 
 [build-system]
 requires = ["setuptools>=42", "wheel"]
diff --git a/src/cli.py b/src/cli.py
index 090c619..46bf5d3 100644
--- a/src/cli.py
+++ b/src/cli.py
@@ -1,6 +1,7 @@
 import sys
 import click
 from src.mood_logger import log_mood, latest_entries
+from src.plot import show as plot_show
 
 @click.group()
 def cli():
@@ -23,5 +24,10 @@ def latest(n):
     for e in entries:
         click.echo(f"{e.date}: {e.rating} – {e.note or ''}")
 
+@cli.command()
+def plot():
+    """Plot the last 30 mood ratings."""
+    plot_show()
+
 if __name__ == "__main__":
     cli()
diff --git a/src/mood_logger.py b/src/mood_logger.py
index 261130a..29d87b4 100644
--- a/src/mood_logger.py
+++ b/src/mood_logger.py
@@ -50,3 +50,15 @@ def latest_entries(
         for row in rows
     ]
     return entries[-n:]
+
+def load_entries(*, file_path: str = "mood.csv") -> List[MoodEntry]:
+    """Return all mood entries from the CSV file."""
+    path = Path(file_path)
+    if not path.exists():
+        return []
+    with path.open(newline="") as csvfile:
+        rows = list(csv.DictReader(csvfile))
+    return [
+        MoodEntry(row["date"], int(row["rating"]), row.get("note") or None)
+        for row in rows
+    ]
diff --git a/src/plot.py b/src/plot.py
new file mode 100644
index 0000000..d8ac3f7
--- /dev/null
+++ b/src/plot.py
@@ -0,0 +1,18 @@
+from datetime import datetime
+from matplotlib import pyplot as plt
+from .mood_logger import load_entries
+
+
+def show(*, file_path: str = "mood.csv") -> None:
+    """Display a line chart of the last 30 mood entries."""
+    entries = load_entries(file_path=file_path)[-30:]
+    if not entries:
+        return
+    dates = [datetime.fromisoformat(e.date) for e in entries]
+    ratings = [e.rating for e in entries]
+    plt.plot(dates, ratings, marker="o")
+    plt.xlabel("Date")
+    plt.ylabel("Rating")
+    plt.gcf().autofmt_xdate()
+    plt.tight_layout()
+    plt.show()
diff --git a/tests/test_plot.py b/tests/test_plot.py
new file mode 100644
index 0000000..67a3e00
--- /dev/null
+++ b/tests/test_plot.py
@@ -0,0 +1,20 @@
+import os
+import matplotlib.pyplot as plt
+from src.plot import show
+from src.mood_logger import log_mood
+import pytest
+
+@pytest.mark.skipif(os.getenv("CI") == "true", reason="Skip on CI")
+def test_show_calls_pyplot_show(tmp_path, monkeypatch):
+    file = tmp_path / "mood.csv"
+    for rating in range(3):
+        log_mood(rating + 1, file_path=str(file))
+
+    called = []
+
+    def fake_show():
+        called.append(True)
+
+    monkeypatch.setattr(plt, "show", fake_show)
+    show(file_path=str(file))
+    assert called