diff --git a/package.json b/package.json
index f42783cc..fb061caa 100644
--- a/package.json
+++ b/package.json
@@ -7,6 +7,7 @@
     "doc": "doc"
   },
   "scripts": {
+    "check-types": "tsc --version",
     "test": "node_modules/.bin/impunity --entry-point src/main.js --force-esm-dirs lib/ src/",
     "start": "node scripts/serve-local.js",
     "build": "node --experimental-modules scripts/build.mjs",
@@ -32,6 +33,7 @@
     "cheerio": "^1.0.0-rc.3",
     "commander": "^6.0.0",
     "core-js": "^3.6.5",
+    "fake-indexeddb": "^3.1.2",
     "finalhandler": "^1.1.1",
     "impunity": "^1.0.0",
     "mdn-polyfills": "^5.20.0",
@@ -52,6 +54,7 @@
     "base64-arraybuffer": "^0.2.0",
     "bs58": "^4.0.1",
     "olm": "https://packages.matrix.org/npm/olm/olm-3.1.4.tgz",
-    "text-encoding": "^0.7.0"
+    "text-encoding": "^0.7.0",
+    "typescript": "^4.0.3"
   }
 }
diff --git a/tsconfig.json b/tsconfig.json
new file mode 100644
index 00000000..c5f53e4d
--- /dev/null
+++ b/tsconfig.json
@@ -0,0 +1,16 @@
+{
+  "compilerOptions": {
+  	"target": "es2020",
+  	"lib": ["es2020", "dom"],
+  	"allowJs": true,
+  	"checkJs": true,
+  	"noEmit": true,
+  	"strict": true,
+  	"strictNullChecks": true,
+  	"strictFunctionTypes": true,
+  	"noImplicitAny": true,
+  	"noImplicitReturns": true,
+  	"noImplicitThis": true
+  },
+  "files": ["src/main.js"]
+}
diff --git a/yarn.lock b/yarn.lock
index f1b9a4be..50798ace 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -952,6 +952,11 @@ base-x@^3.0.2:
   dependencies:
     safe-buffer "^5.0.1"
 
+base64-arraybuffer-es6@^0.6.0:
+  version "0.6.0"
+  resolved "https://registry.yarnpkg.com/base64-arraybuffer-es6/-/base64-arraybuffer-es6-0.6.0.tgz#036f79f57588dca0018de7792ddf149299382007"
+  integrity sha512-57nLqKj4ShsDwFJWJsM4sZx6u60WbCge35rWRSevUwqxDtRwwxiKAO800zD2upPv4CfdWjQp//wSLar35nDKvA==
+
 base64-arraybuffer@^0.2.0:
   version "0.2.0"
   resolved "https://registry.yarnpkg.com/base64-arraybuffer/-/base64-arraybuffer-0.2.0.tgz#4b944fac0191aa5907afe2d8c999ccc57ce80f45"
@@ -1070,6 +1075,11 @@ core-js-compat@^3.6.2:
     browserslist "^4.8.5"
     semver "7.0.0"
 
+core-js@^2.5.3:
+  version "2.6.11"
+  resolved "https://registry.yarnpkg.com/core-js/-/core-js-2.6.11.tgz#38831469f9922bded8ee21c9dc46985e0399308c"
+  integrity sha512-5wjnpaT/3dV+XB4borEsnAYQchn00XSgTAWKDkEqv+K8KevjbzmofK6hfJ9TZIlpj2N0xQpazy7PiRQiWHqzWg==
+
 core-js@^3.6.5:
   version "3.6.5"
   resolved "https://registry.yarnpkg.com/core-js/-/core-js-3.6.5.tgz#7395dc273af37fb2e50e9bd3d9fe841285231d1a"
@@ -1157,6 +1167,13 @@ domelementtype@^2.0.1:
   resolved "https://registry.yarnpkg.com/domelementtype/-/domelementtype-2.0.1.tgz#1f8bdfe91f5a78063274e803b4bdcedf6e94f94d"
   integrity sha512-5HOHUDsYZWV8FGWN0Njbr/Rn7f/eWSQi1v7+HsUVwXgn8nWWlL64zKDkS0n8ZmQ3mlWOMuXOnR+7Nx/5tMO5AQ==
 
+domexception@^1.0.1:
+  version "1.0.1"
+  resolved "https://registry.yarnpkg.com/domexception/-/domexception-1.0.1.tgz#937442644ca6a31261ef36e3ec677fe805582c90"
+  integrity sha512-raigMkn7CJNNo6Ihro1fzG7wr3fHuYVytzquZKX5n0yizGsTcYgzdIUwj1X9pK0VvjeihV+XiclP+DjwbsSKug==
+  dependencies:
+    webidl-conversions "^4.0.2"
+
 domhandler@^2.3.0:
   version "2.4.2"
   resolved "https://registry.yarnpkg.com/domhandler/-/domhandler-2.4.2.tgz#8805097e933d65e85546f726d60f5eb88b44f803"
@@ -1250,6 +1267,14 @@ extend@^3.0.1:
   resolved "https://registry.yarnpkg.com/extend/-/extend-3.0.2.tgz#f8b1136b4071fbd8eb140aff858b1019ec2915fa"
   integrity sha512-fjquC59cD7CyW6urNXK0FBufkZcoiGG80wTuPujX590cB5Ttln20E2UB4S/WARVqhXffZl2LNgS+gQdPIIim/g==
 
+fake-indexeddb@^3.1.2:
+  version "3.1.2"
+  resolved "https://registry.yarnpkg.com/fake-indexeddb/-/fake-indexeddb-3.1.2.tgz#8073a12ed3b254f7afc064f3cc2629f0110a5303"
+  integrity sha512-W60eRBrE8r9o/EePyyUc63sr2I/MI9p3zVwLlC1WI1xdmQVqqM6+wec9KDWDz2EZyvJKhrDvy3cGC6hK8L1pfg==
+  dependencies:
+    realistic-structured-clone "^2.0.1"
+    setimmediate "^1.0.5"
+
 finalhandler@^1.1.1:
   version "1.1.2"
   resolved "https://registry.yarnpkg.com/finalhandler/-/finalhandler-1.1.2.tgz#b7e7d000ffd11938d0fdb053506f6ebabe9f587d"
@@ -1421,6 +1446,11 @@ levenary@^1.1.1:
   dependencies:
     leven "^3.1.0"
 
+lodash.sortby@^4.7.0:
+  version "4.7.0"
+  resolved "https://registry.yarnpkg.com/lodash.sortby/-/lodash.sortby-4.7.0.tgz#edd14c824e2cc9c1e0b0a1b42bb5210516a42438"
+  integrity sha1-7dFMgk4sycHgsKG0K7UhBRakJDg=
+
 lodash@^4.15.0:
   version "4.17.15"
   resolved "https://registry.yarnpkg.com/lodash/-/lodash-4.17.15.tgz#b447f6670a0455bbfeedd11392eff330ea097548"
@@ -1654,6 +1684,11 @@ postcss@^7.0.2, postcss@^7.0.26, postcss@^7.0.32:
     source-map "^0.6.1"
     supports-color "^6.1.0"
 
+punycode@^2.1.1:
+  version "2.1.1"
+  resolved "https://registry.yarnpkg.com/punycode/-/punycode-2.1.1.tgz#b58b010ac40c22c5657616c8d2c2c02c7bf479ec"
+  integrity sha512-XRsRjdf+j5ml+y/6GKHPZbrF/8p2Yga0JPtdqTIY2Xe5ohJPD9saDJJLPvp9+NSBprVvevdXZybnj2cv8OEd0A==
+
 range-parser@~1.2.1:
   version "1.2.1"
   resolved "https://registry.yarnpkg.com/range-parser/-/range-parser-1.2.1.tgz#3cf37023d199e1c24d1a55b84800c2f3e6468031"
@@ -1675,6 +1710,16 @@ readable-stream@^3.1.1:
     string_decoder "^1.1.1"
     util-deprecate "^1.0.1"
 
+realistic-structured-clone@^2.0.1:
+  version "2.0.2"
+  resolved "https://registry.yarnpkg.com/realistic-structured-clone/-/realistic-structured-clone-2.0.2.tgz#2f8ec225b1f9af20efc79ac96a09043704414959"
+  integrity sha512-5IEvyfuMJ4tjQOuKKTFNvd+H9GSbE87IcendSBannE28PTrbolgaVg5DdEApRKhtze794iXqVUFKV60GLCNKEg==
+  dependencies:
+    core-js "^2.5.3"
+    domexception "^1.0.1"
+    typeson "^5.8.2"
+    typeson-registry "^1.0.0-alpha.20"
+
 regenerate-unicode-properties@^8.2.0:
   version "8.2.0"
   resolved "https://registry.yarnpkg.com/regenerate-unicode-properties/-/regenerate-unicode-properties-8.2.0.tgz#e5de7111d655e7ba60c057dbe9ff37c87e65cdec"
@@ -1813,6 +1858,11 @@ serve-static@^1.13.2:
     parseurl "~1.3.3"
     send "0.17.1"
 
+setimmediate@^1.0.5:
+  version "1.0.5"
+  resolved "https://registry.yarnpkg.com/setimmediate/-/setimmediate-1.0.5.tgz#290cbb232e306942d7d7ea9b83732ab7856f8285"
+  integrity sha1-KQy7Iy4waULX1+qbg3Mqt4VvgoU=
+
 setprototypeof@1.1.1:
   version "1.1.1"
   resolved "https://registry.yarnpkg.com/setprototypeof/-/setprototypeof-1.1.1.tgz#7e95acb24aa92f5885e0abef5ba131330d4ae683"
@@ -1879,6 +1929,32 @@ toidentifier@1.0.0:
   resolved "https://registry.yarnpkg.com/toidentifier/-/toidentifier-1.0.0.tgz#7e1be3470f1e77948bc43d94a3c8f4d7752ba553"
   integrity sha512-yaOH/Pk/VEhBWWTlhI+qXxDFXlejDGcQipMlyxda9nthulaxLZUNcUqFxokp0vcYnvteJln5FNQDRrxj3YcbVw==
 
+tr46@^2.0.2:
+  version "2.0.2"
+  resolved "https://registry.yarnpkg.com/tr46/-/tr46-2.0.2.tgz#03273586def1595ae08fedb38d7733cee91d2479"
+  integrity sha512-3n1qG+/5kg+jrbTzwAykB5yRYtQCTqOGKq5U5PE3b0a1/mzo6snDhjGS0zJVJunO0NrT3Dg1MLy5TjWP/UJppg==
+  dependencies:
+    punycode "^2.1.1"
+
+typescript@^4.0.3:
+  version "4.0.3"
+  resolved "https://registry.yarnpkg.com/typescript/-/typescript-4.0.3.tgz#153bbd468ef07725c1df9c77e8b453f8d36abba5"
+  integrity sha512-tEu6DGxGgRJPb/mVPIZ48e69xCn2yRmCgYmDugAVwmJ6o+0u1RI18eO7E7WBTLYLaEVVOhwQmcdhQHweux/WPg==
+
+typeson-registry@^1.0.0-alpha.20:
+  version "1.0.0-alpha.38"
+  resolved "https://registry.yarnpkg.com/typeson-registry/-/typeson-registry-1.0.0-alpha.38.tgz#42b19c21997ab80e38b3c67d6c1aad1499fea5b9"
+  integrity sha512-6lt2IhbNT9hyow5hljZqjWtVDXBIaC1X8bBGlBva0Pod2f42g23bVqww09ruquwSC48I8BSSCPi+B2dFHM5ihQ==
+  dependencies:
+    base64-arraybuffer-es6 "^0.6.0"
+    typeson "^5.18.2"
+    whatwg-url "^8.1.0"
+
+typeson@^5.18.2, typeson@^5.8.2:
+  version "5.18.2"
+  resolved "https://registry.yarnpkg.com/typeson/-/typeson-5.18.2.tgz#0d217fc0e11184a66aa7ca0076d9aa7707eb7bc2"
+  integrity sha512-Vetd+OGX05P4qHyHiSLdHZ5Z5GuQDrHHwSdjkqho9NSCYVSLSfRMjklD/unpHH8tXBR9Z/R05rwJSuMpMFrdsw==
+
 unicode-canonical-property-names-ecmascript@^1.0.4:
   version "1.0.4"
   resolved "https://registry.yarnpkg.com/unicode-canonical-property-names-ecmascript/-/unicode-canonical-property-names-ecmascript-1.0.4.tgz#2619800c4c825800efdd8343af7dd9933cbe2818"
@@ -1912,6 +1988,25 @@ util-deprecate@^1.0.1:
   resolved "https://registry.yarnpkg.com/util-deprecate/-/util-deprecate-1.0.2.tgz#450d4dc9fa70de732762fbd2d4a28981419a0ccf"
   integrity sha1-RQ1Nyfpw3nMnYvvS1KKJgUGaDM8=
 
+webidl-conversions@^4.0.2:
+  version "4.0.2"
+  resolved "https://registry.yarnpkg.com/webidl-conversions/-/webidl-conversions-4.0.2.tgz#a855980b1f0b6b359ba1d5d9fb39ae941faa63ad"
+  integrity sha512-YQ+BmxuTgd6UXZW3+ICGfyqRyHXVlD5GtQr5+qjiNW7bF0cqrzX500HVXPBOvgXb5YnzDd+h0zqyv61KUD7+Sg==
+
+webidl-conversions@^6.1.0:
+  version "6.1.0"
+  resolved "https://registry.yarnpkg.com/webidl-conversions/-/webidl-conversions-6.1.0.tgz#9111b4d7ea80acd40f5270d666621afa78b69514"
+  integrity sha512-qBIvFLGiBpLjfwmYAaHPXsn+ho5xZnGvyGvsarywGNc8VyQJUMHJ8OBKGGrPER0okBeMDaan4mNBlgBROxuI8w==
+
+whatwg-url@^8.1.0:
+  version "8.2.2"
+  resolved "https://registry.yarnpkg.com/whatwg-url/-/whatwg-url-8.2.2.tgz#85e7f9795108b53d554cec640b2e8aee2a0d4bfd"
+  integrity sha512-PcVnO6NiewhkmzV0qn7A+UZ9Xx4maNTI+O+TShmfE4pqjoCMwUMjkvoNhNHPTvgR7QH9Xt3R13iHuWy2sToFxQ==
+  dependencies:
+    lodash.sortby "^4.7.0"
+    tr46 "^2.0.2"
+    webidl-conversions "^6.1.0"
+
 wrappy@1:
   version "1.0.2"
   resolved "https://registry.yarnpkg.com/wrappy/-/wrappy-1.0.2.tgz#b5243d8f3ec1aa35f1364605bc0d1036e30ab69f"