diff --git a/Makefile b/Makefile
index cd5ba44..c1ea720 100644
--- a/Makefile
+++ b/Makefile
@@ -1,5 +1,9 @@
 export PATH := bin:$(PATH)
 
+.PHONY: debug
+debug:
+	node builder/build.js python riju-lang-python.deb
+
 .PHONY: build-image
 build-image:
 	docker build . -f docker/Dockerfile.build -t riju:build
diff --git a/build/build.js b/build/build.js
deleted file mode 100644
index e69de29..0000000
diff --git a/builder/build.js b/builder/build.js
new file mode 100644
index 0000000..64a4e2f
--- /dev/null
+++ b/builder/build.js
@@ -0,0 +1,95 @@
+const child_process = require("child_process");
+const fs = require("fs").promises;
+const path = require("path");
+const process = require("process");
+
+const tmp = require("tmp-promise");
+const YAML = require("yaml");
+
+// The build scripts in the language configs assume a specific build
+// environment, with these parameters:
+//
+// * the working directory starts out empty
+// * the ${pkg} environment variable has been set to an absolute path
+//   to the directory where the package should be built
+// * we are using bash with 'set -euxo pipefail'
+
+// Read the YAML config file for the language with the given string ID
+// and return it as an object.
+async function readLangConfig(lang) {
+  return YAML.parse(await fs.readFile(`langs/${lang}.yaml`, "utf-8"));
+}
+
+// Given a shell command as a string, execute it with Bash.
+async function runCommand(cmd) {
+  return new Promise((resolve, reject) => {
+    const proc = child_process.spawn("bash", ["-c", ...cmd]);
+    proc.on("error", reject);
+    proc.on("close", (code) => {
+      if (code === 0) {
+        resolve();
+      } else {
+        reject(new Error(`command exited with code ${code}`));
+      }
+    });
+  });
+}
+
+// Given a language config object, assuming that the environment has
+// already been set up properly (see top of this file for details),
+// run all the commands needed to build a package, and put the
+// resulting deb file into debPath.
+async function buildPackage(langConfig, debPath) {
+  const {
+    id,
+    name,
+    install: { apt, pip, manual },
+  } = langConfig;
+  const timestamp = new Date().getTime();
+  let debianControlData = `\
+Package: riju-lang-${id}
+Version: ${timestamp}
+Architecture: amd64
+Maintainer: Radon Rosborough <radon.neon@gmail.com>
+Description: The ${name} language packaged for Riju
+`;
+  if (apt.length > 0) {
+    debianControlData += `\
+Depends: ${apt.join(", ")}
+`;
+  }
+  await fs.mkdir("DEBIAN");
+  await fs.writeFile("DEBIAN/control", debianControlData);
+  await runCommand([
+    "fakeroot",
+    "dpkg-deb",
+    "--build",
+    process.env.pkg,
+    debPath,
+  ]);
+}
+
+async function main() {
+  const args = process.argv.slice(2);
+  if (args.length !== 2) {
+    console.error("usage: build.js LANG DEB");
+    process.exit(1);
+  }
+  let [lang, debPath] = args;
+  debPath = path.join(process.cwd(), debPath);
+  const langConfig = await readLangConfig(lang);
+  await tmp.withDir(async (o) => {
+    const buildDir = o.path;
+    await tmp.withDir(async (o) => {
+      const pkgDir = o.path;
+      process.chdir(buildDir);
+      process.env.pkg = pkgDir;
+      await buildPackage(langConfig, debPath);
+    });
+  });
+}
+
+main().catch((err) => {
+  console.error(err);
+  process.exit(1);
+});
diff --git a/build/debug.js b/builder/debug.js
similarity index 100%
rename from build/debug.js
rename to builder/debug.js
diff --git a/langs/python.yaml b/langs/python.yaml
index c2df720..608d390 100644
--- a/langs/python.yaml
+++ b/langs/python.yaml
@@ -15,11 +15,11 @@ install:
   manual:
     - |
       xml="$(curl -sSL "https://pvsc.blob.core.windows.net/python-language-server-stable?restype=container&comp=list&prefix=Python-Language-Server-linux-x64")"
-      nupkg="$(echo "$xml" | grep -Eo 'https://[^<]+\.nupkg' | tail -n1)"
-      wget "${nupkg}"
-      unzip -d /opt/mspyls Python-Language-Server-linux-x64.*.nupkg
-      chmod +x /opt/mspyls/Microsoft.Python.LanguageServer
-      ln -s /opt/mspyls/Microsoft.Python.LanguageServer /usr/local/bin/Microsoft.Python.LanguageServer
+      url="$(echo "${xml}" | grep -Eo 'https://[^<]+\.nupkg' | tail -n1)"
+      wget "${url}"
+      unzip -d "${pkg}/opt/mspyls" Python-Language-Server-linux-x64.*.nupkg
+      chmod +x "${pkg}/opt/mspyls/Microsoft.Python.LanguageServer"
+      ln -s "${pkg}/opt/mspyls/Microsoft.Python.LanguageServer" /usr/local/bin/Microsoft.Python.LanguageServer
 
 repl: >-
   python3 -u
diff --git a/package.json b/package.json
index 7b0e167..d414df1 100644
--- a/package.json
+++ b/package.json
@@ -4,6 +4,7 @@
   "license": "MIT",
   "private": true,
   "dependencies": {
+    "tmp-promise": "^3.0.2",
     "yaml": "^1.10.0"
   }
 }
diff --git a/yarn.lock b/yarn.lock
index a24537e..5ecae73 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -2,6 +2,99 @@
 # yarn lockfile v1
 
 
+balanced-match@^1.0.0:
+  version "1.0.0"
+  resolved "https://registry.yarnpkg.com/balanced-match/-/balanced-match-1.0.0.tgz#89b4d199ab2bee49de164ea02b89ce462d71b767"
+  integrity sha1-ibTRmasr7kneFk6gK4nORi1xt2c=
+
+brace-expansion@^1.1.7:
+  version "1.1.11"
+  resolved "https://registry.yarnpkg.com/brace-expansion/-/brace-expansion-1.1.11.tgz#3c7fcbf529d87226f3d2f52b966ff5271eb441dd"
+  integrity sha512-iCuPHDFgrHX7H2vEI/5xpz07zSHB00TpugqhmYtVmMO6518mCuRMoOYFldEBl0g187ufozdaHgWKcYFb61qGiA==
+  dependencies:
+    balanced-match "^1.0.0"
+    concat-map "0.0.1"
+
+concat-map@0.0.1:
+  version "0.0.1"
+  resolved "https://registry.yarnpkg.com/concat-map/-/concat-map-0.0.1.tgz#d8a96bd77fd68df7793a73036a3ba0d5405d477b"
+  integrity sha1-2Klr13/Wjfd5OnMDajug1UBdR3s=
+
+fs.realpath@^1.0.0:
+  version "1.0.0"
+  resolved "https://registry.yarnpkg.com/fs.realpath/-/fs.realpath-1.0.0.tgz#1504ad2523158caa40db4a2787cb01411994ea4f"
+  integrity sha1-FQStJSMVjKpA20onh8sBQRmU6k8=
+
+glob@^7.1.3:
+  version "7.1.6"
+  resolved "https://registry.yarnpkg.com/glob/-/glob-7.1.6.tgz#141f33b81a7c2492e125594307480c46679278a6"
+  integrity sha512-LwaxwyZ72Lk7vZINtNNrywX0ZuLyStrdDtabefZKAY5ZGJhVtgdznluResxNmPitE0SAO+O26sWTHeKSI2wMBA==
+  dependencies:
+    fs.realpath "^1.0.0"
+    inflight "^1.0.4"
+    inherits "2"
+    minimatch "^3.0.4"
+    once "^1.3.0"
+    path-is-absolute "^1.0.0"
+
+inflight@^1.0.4:
+  version "1.0.6"
+  resolved "https://registry.yarnpkg.com/inflight/-/inflight-1.0.6.tgz#49bd6331d7d02d0c09bc910a1075ba8165b56df9"
+  integrity sha1-Sb1jMdfQLQwJvJEKEHW6gWW1bfk=
+  dependencies:
+    once "^1.3.0"
+    wrappy "1"
+
+inherits@2:
+  version "2.0.4"
+  resolved "https://registry.yarnpkg.com/inherits/-/inherits-2.0.4.tgz#0fa2c64f932917c3433a0ded55363aae37416b7c"
+  integrity sha512-k/vGaX4/Yla3WzyMCvTQOXYeIHvqOKtnqBduzTHpzpQZzAskKMhZ2K+EnBiSM9zGSoIFeMpXKxa4dYeZIQqewQ==
+
+minimatch@^3.0.4:
+  version "3.0.4"
+  resolved "https://registry.yarnpkg.com/minimatch/-/minimatch-3.0.4.tgz#5166e286457f03306064be5497e8dbb0c3d32083"
+  integrity sha512-yJHVQEhyqPLUTgt9B83PXu6W3rx4MvvHvSUvToogpwoGDOUQ+yDrR0HRot+yOCdCO7u4hX3pWft6kWBBcqh0UA==
+  dependencies:
+    brace-expansion "^1.1.7"
+
+once@^1.3.0:
+  version "1.4.0"
+  resolved "https://registry.yarnpkg.com/once/-/once-1.4.0.tgz#583b1aa775961d4b113ac17d9c50baef9dd76bd1"
+  integrity sha1-WDsap3WWHUsROsF9nFC6753Xa9E=
+  dependencies:
+    wrappy "1"
+
+path-is-absolute@^1.0.0:
+  version "1.0.1"
+  resolved "https://registry.yarnpkg.com/path-is-absolute/-/path-is-absolute-1.0.1.tgz#174b9268735534ffbc7ace6bf53a5a9e1b5c5f5f"
+  integrity sha1-F0uSaHNVNP+8es5r9TpanhtcX18=
+
+rimraf@^3.0.0:
+  version "3.0.2"
+  resolved "https://registry.yarnpkg.com/rimraf/-/rimraf-3.0.2.tgz#f1a5402ba6220ad52cc1282bac1ae3aa49fd061a"
+  integrity sha512-JZkJMZkAGFFPP2YqXZXPbMlMBgsxzE8ILs4lMIX/2o0L9UBw9O/Y3o6wFw/i9YLapcUJWwqbi3kdxIPdC62TIA==
+  dependencies:
+    glob "^7.1.3"
+
+tmp-promise@^3.0.2:
+  version "3.0.2"
+  resolved "https://registry.yarnpkg.com/tmp-promise/-/tmp-promise-3.0.2.tgz#6e933782abff8b00c3119d63589ca1fb9caaa62a"
+  integrity sha512-OyCLAKU1HzBjL6Ev3gxUeraJNlbNingmi8IrHHEsYH8LTmEuhvYfqvhn2F/je+mjf4N58UmZ96OMEy1JanSCpA==
+  dependencies:
+    tmp "^0.2.0"
+
+tmp@^0.2.0:
+  version "0.2.1"
+  resolved "https://registry.yarnpkg.com/tmp/-/tmp-0.2.1.tgz#8457fc3037dcf4719c251367a1af6500ee1ccf14"
+  integrity sha512-76SUhtfqR2Ijn+xllcI5P1oyannHNHByD80W1q447gU3mp9G9PSpGdWmjUOHRDPiHYacIk66W7ubDTuPF3BEtQ==
+  dependencies:
+    rimraf "^3.0.0"
+
+wrappy@1:
+  version "1.0.2"
+  resolved "https://registry.yarnpkg.com/wrappy/-/wrappy-1.0.2.tgz#b5243d8f3ec1aa35f1364605bc0d1036e30ab69f"
+  integrity sha1-tSQ9jz7BqjXxNkYFvA0QNuMKtp8=
+
 yaml@^1.10.0:
   version "1.10.0"
   resolved "https://registry.yarnpkg.com/yaml/-/yaml-1.10.0.tgz#3b593add944876077d4d683fee01081bd9fff31e"