diff --git a/backend/src/langs.ts b/backend/src/langs.ts
index fd1afe1..3b76f32 100644
--- a/backend/src/langs.ts
+++ b/backend/src/langs.ts
@@ -395,6 +395,17 @@ int main() {
 `,
     skip: ["lsp"],
   },
+  cat: {
+    aliases: ["cat-language"],
+    name: "Cat",
+    repl: "NODE_PATH=/opt/cat node /opt/cat/repl.js",
+    input: "123 234 mul",
+    main: "main.cat",
+    run: "NODE_PATH=/opt/cat node /opt/cat/repl.js main.cat",
+    hello: "72,101,108,108,111,44,32,119,111,114,108,100,33,10",
+    template: `72 101 108 108 111 44 32 119 111 114 108 100 33 10
+`,
+  },
   ceylon: {
     name: "Ceylon",
     main: "source/main.ceylon",
diff --git a/scripts/docker-install-phase6.bash b/scripts/docker-install-phase6.bash
index eac280c..4c30a43 100755
--- a/scripts/docker-install-phase6.bash
+++ b/scripts/docker-install-phase6.bash
@@ -25,6 +25,12 @@ wget -nv https://www.ioccc.org/2012/tromp/tromp.c
 clang tromp.c -Wno-everything -DInt=long -DX=8 -DA=500000 -o /usr/local/bin/tromp
 rm tromp.c
 
+# Cat
+git clone https://github.com/cdiggins/cat-language.git /opt/cat
+pushd /opt/cat >/dev/null
+npm install
+popd >/dev/null
+
 # Erlang
 git clone https://github.com/erlang-ls/erlang_ls.git
 pushd erlang_ls >/dev/null
diff --git a/scripts/docker-install-phase7.bash b/scripts/docker-install-phase7.bash
index 420214e..6a58887 100755
--- a/scripts/docker-install-phase7.bash
+++ b/scripts/docker-install-phase7.bash
@@ -130,6 +130,29 @@ while True:
 EOF
 chmod +x /usr/local/bin/brainf-repl
 
+# Cat
+tee /opt/cat/repl.js >/dev/null <<"EOF"
+const fs = require("fs");
+const repl = require("repl");
+
+const args = process.argv.slice(2);
+if (args.length > 1) {
+  console.error("usage: repl.js [FILE]");
+  process.exit(1);
+}
+
+const program = args.length === 1 ? fs.readFileSync(args[0], "utf-8") : null;
+
+const cat = require("cat");
+const ce = new cat.CatLanguage.CatEvaluator();
+
+if (program !== null) {
+  ce.eval(program);
+}
+
+repl.start({prompt: "cat> ", eval: (cmd, context, filename, callback) => callback(null, ce.eval(cmd))});
+EOF
+
 # Haskell
 mkdir -p /opt/haskell
 tee /opt/haskell/hie.yaml >/dev/null <<"EOF"