diff --git a/.dockerignore b/.dockerignore
new file mode 100644
index 0000000..93f3c0d
--- /dev/null
+++ b/.dockerignore
@@ -0,0 +1,12 @@
+# Rust build artifacts — by far the largest directory, not needed at build time.
+target/
+
+# Not used by the Dockerfile (builder/ is mounted as a volume at runtime).
+builder/
+docs/
+infra/
+proxy/
+plan.md
+
+# Never send version-control metadata.
+.git/