diff --git a/Makefile b/Makefile
index 5b8208e..a46692b 100644
--- a/Makefile
+++ b/Makefile
@@ -65,6 +65,10 @@ serve-docs: $(VENV)
 manpage: $(VENV)
 	help2man $(BIN)/blag --no-info -n "blog-aware, static site generator" -o debian/blag.1
 
+.PHONY: benchmark
+benchmark: $(VENV)
+	$(BIN)/pytest --no-cov -capture=no -rA tests/benchmark.py
+
 .PHONY: clean
 clean:
 	rm -rf build dist *.egg-info
diff --git a/blag/blag.py b/blag/blag.py
index ed6db15..9f87cc1 100644
--- a/blag/blag.py
+++ b/blag/blag.py
@@ -323,6 +323,18 @@ def process_markdown(
     for src, dst in convertibles:
         logger.debug(f"Processing {src}")
 
+        # see first if the dst actually needs re-building. for that we compare
+        # the mtimes and assume mtime_dst > mtime_src means that it needs not
+        # to be rebuilt
+        if os.path.exists(f"{output_dir}/{dst}"):
+            mtime_src = os.stat(f"{input_dir}/{src}").st_mtime
+            mtime_dst = os.stat(f"{output_dir}/{dst}").st_mtime
+            if mtime_dst >= mtime_src:
+                logger.debug(
+                    "Skipping, as target exists and is newer than source."
+                )
+                continue
+
         with open(f"{input_dir}/{src}") as fh:
             body = fh.read()
 
diff --git a/tests/benchmark.py b/tests/benchmark.py
new file mode 100644
index 0000000..9dbc309
--- /dev/null
+++ b/tests/benchmark.py
@@ -0,0 +1,37 @@
+"""Benchmark the performance of the blag build command."""
+
+import logging
+import os
+from argparse import Namespace
+
+from pytest import LogCaptureFixture
+
+import blag
+from blag.blag import build
+
+
+def test_performance(args: Namespace, caplog: LogCaptureFixture) -> None:
+    """Test performance of the build command."""
+    caplog.set_level(logging.ERROR)
+
+    FILES = 10000
+    print(f"Generating {FILES} markdown files")
+    # create random markdown files in the content directory
+    with open(os.path.join(blag.__path__[0], "content", "testpage.md")) as fh:
+        markdown = fh.read()
+    for i in range(FILES):
+        with open(f"content/{i}.md", "w") as f:
+            f.write(markdown)
+            f.write(str(i))
+
+    from time import time
+
+    t = time()
+    build(args)
+    t_first = time() - t
+
+    t = time()
+    build(args)
+    t_second = time() - t
+    print(f"First run: {t_first:.2f}s, second run: {t_second:.2f}s")
+    print(f"Speedup: {t_first/t_second:.2f}")