diff --git a/.gitattributes b/.gitattributes
new file mode 100644
index 00000000..5bad95e0
--- /dev/null
+++ b/.gitattributes
@@ -0,0 +1,21 @@
+# Exclude build/test files from archive (reduce package size)
+/.github            export-ignore
+/.phive             export-ignore
+/build              export-ignore
+/docs               export-ignore
+/ext                export-ignore
+/resources          export-ignore
+/tests              export-ignore
+/tests_old          export-ignore
+/.editorconfig      export-ignore
+/.gitattributes     export-ignore
+/.gitignore         export-ignore
+/.php-cs-fixer.php  export-ignore
+/captainhook.json   export-ignore
+/install-runtime.sh export-ignore
+/package.json       export-ignore
+/phpstan.neon       export-ignore
+/phpunit.xml.dist   export-ignore
+
+# Configure diff output
+*.php diff=php