diff --git a/README.md b/README.md
index 96bf7ed..b50bccb 100644
--- a/README.md
+++ b/README.md
@@ -1 +1,26 @@
 # dotfiles
+
+<!-- LINE-COUNT-START -->
+This repo has **20,055** lines of technical debt.
+
+| File Type | Lines | Percentage |
+|-----------|------:|-----------:|
+| .py | 11,441 | 57.0% |
+| .nix | 4,471 | 22.3% |
+| .yaml | 1,121 | 5.6% |
+| .html | 1,009 | 5.0% |
+| .json | 555 | 2.8% |
+| .yml | 479 | 2.4% |
+| .toml | 290 | 1.4% |
+| .css | 212 | 1.1% |
+| .gitignore | 199 | 1.0% |
+| .md | 75 | 0.4% |
+| .cfg | 73 | 0.4% |
+| .sh | 48 | 0.2% |
+| .mako | 36 | 0.2% |
+| .LICENSE | 21 | 0.1% |
+| .conf | 17 | 0.1% |
+| .Gemfile | 4 | 0.0% |
+| .svg | 3 | 0.0% |
+| .new | 1 | 0.0% |
+<!-- LINE-COUNT-END -->
diff --git a/tools/line_counter.py b/tools/line_counter.py
new file mode 100644
index 0000000..bb906fe
--- /dev/null
+++ b/tools/line_counter.py
@@ -0,0 +1,86 @@
+"""Count lines of code in the repository, grouped by file type."""
+
+from __future__ import annotations
+
+import subprocess
+from collections import defaultdict
+from pathlib import Path
+
+
+def get_tracked_files() -> list[str]:
+    """Get all git-tracked files."""
+    result = subprocess.run(
+        ["git", "ls-files"],  # noqa: S603, S607
+        capture_output=True,
+        text=True,
+        check=True,
+    )
+    return [f for f in result.stdout.strip().splitlines() if f]
+
+
+def count_lines(filepath: str) -> int:
+    """Count lines in a file, returning 0 for binary files."""
+    try:
+        return len(Path(filepath).read_text(encoding="utf-8").splitlines())
+    except (UnicodeDecodeError, OSError):
+        return 0
+
+
+def count_lines_by_type() -> dict[str, int]:
+    """Count lines grouped by file extension."""
+    lines_by_type: dict[str, int] = defaultdict(int)
+    for filepath in get_tracked_files():
+        ext = Path(filepath).suffix.lstrip(".")
+        if not ext:
+            ext = Path(filepath).name
+        lines_by_type[ext] += count_lines(filepath)
+    # Exclude binary/non-code files
+    for key in ("png", "lock"):
+        lines_by_type.pop(key, None)
+    return dict(sorted(lines_by_type.items(), key=lambda x: x[1], reverse=True))
+
+
+def format_report() -> str:
+    """Generate a formatted line count report."""
+    lines_by_type = count_lines_by_type()
+    total = sum(lines_by_type.values())
+
+    lines = [
+        f"This repo has **{total:,}** lines of technical debt.",
+        "",
+        "| File Type | Lines | Percentage |",
+        "|-----------|------:|-----------:|",
+    ]
+    for ext, count in lines_by_type.items():
+        if count > 0:
+            pct = count / total * 100
+            prefix = "." if not ext.startswith(".") else ""
+            lines.append(f"| {prefix}{ext} | {count:,} | {pct:.1f}% |")
+
+    return "\n".join(lines)
+
+
+def update_readme() -> None:
+    """Update README.md with the line count report."""
+    readme_path = Path("README.md")
+    report = format_report()
+
+    start_marker = "<!-- LINE-COUNT-START -->"
+    end_marker = "<!-- LINE-COUNT-END -->"
+
+    content = readme_path.read_text(encoding="utf-8")
+
+    section = f"{start_marker}\n{report}\n{end_marker}"
+
+    if start_marker in content:
+        start = content.index(start_marker)
+        end = content.index(end_marker) + len(end_marker)
+        content = content[:start] + section + content[end:]
+    else:
+        content = content.rstrip() + "\n\n" + section + "\n"
+
+    readme_path.write_text(content, encoding="utf-8")
+
+
+if __name__ == "__main__":
+    update_readme()