diff --git a/profiles/opencode.nix b/profiles/opencode.nix
index bbc097f..4f01b5d 100644
--- a/profiles/opencode.nix
+++ b/profiles/opencode.nix
@@ -67,6 +67,10 @@
 			source = ./opencode/tool;
 			recursive = true;
 		};
+		"opencode/plugin" = {
+			source = ./opencode/plugin;
+			recursive = true;
+		};
 		"opencode/oh-my-opencode.json".text =
 			builtins.toJSON {
 				"$schema" = "https://raw.githubusercontent.com/code-yeongyu/oh-my-opencode/master/assets/oh-my-opencode.schema.json";
diff --git a/profiles/opencode/plugin/block-git.ts b/profiles/opencode/plugin/block-git.ts
new file mode 100644
index 0000000..acafd04
--- /dev/null
+++ b/profiles/opencode/plugin/block-git.ts
@@ -0,0 +1,18 @@
+import type { Plugin } from "@opencode-ai/plugin";
+
+const GIT_PATTERN = /(?:^|[;&|]\s*|&&\s*|\|\|\s*|\$\(\s*|`\s*)git\s/;
+
+export const BlockGitPlugin: Plugin = async () => {
+	return {
+		"tool.execute.before": async (input, output) => {
+			if (input.tool === "bash") {
+				const command = output.args.command as string;
+				if (GIT_PATTERN.test(command)) {
+					throw new Error(
+						"This project uses jj, only use `jj` commands, not `git`.",
+					);
+				}
+			}
+		},
+	};
+};