diff --git a/.dockerignore b/.dockerignore
new file mode 100644
index 0000000..f7bbb97
--- /dev/null
+++ b/.dockerignore
@@ -0,0 +1,18 @@
+# The image build installs its own deps (npm ci, pip install) inside the stages, so none of
+# these belong in the build context. Keeps the context small and the build fast.
+.git
+**/node_modules
+**/.venv
+**/__pycache__
+**/.pytest_cache
+**/.mypy_cache
+backend/tests
+backend/static
+deploy/*.s9pk
+deploy/javascript
+*.xlsx
+SECURITY-AUDIT.md
+*.md
+!README.md
+.DS_Store
+**/.DS_Store