diff --git a/firebase.json b/firebase.json
index 060c76ca..29b08290 100644
--- a/firebase.json
+++ b/firebase.json
@@ -1,5 +1,6 @@
 {
   "functions": {
-    "predeploy": "npm --prefix \"$RESOURCE_DIR\" run build"
+    "predeploy": "npm --prefix \"$RESOURCE_DIR\" run build",
+    "runtime": "nodejs12"
   }
 }
diff --git a/functions/README.md b/functions/README.md
new file mode 100644
index 00000000..51db0793
--- /dev/null
+++ b/functions/README.md
@@ -0,0 +1,48 @@
+**NOTE: Adapted from One Word's /functions doc. Fix any errors you see!**
+
+# Firestore Cloud Functions
+
+This is code that doesn't make sense on the frontend client, e.g.
+
+- Long-running or slow operation (database)
+- Tasks that need to be run every so often (syncing email list to Mailjet)
+- Anything we should't trust to clients (secrets, auth)
+
+If you want to make and test changes, you'll have to do a bit of setup...
+
+## Installing
+
+Adapted from https://firebase.google.com/docs/functions/get-started
+
+0. `$ cd functions` to switch to this folder
+1. `$ yarn global add firebase-tools` to install the Firebase CLI globally
+2. `$ yarn` to install JS dependencies
+3. `$ firebase functions:config:get > .runtimeconfig.json` to cache secrets for local dev (TODO: maybe not for Manifold)
+4. `$ firebase use dev` to choose the dev project
+
+## Developing locally
+
+1. `$ firebase login` if you aren't logged into Firebase via commandline yet.
+2. `$ yarn dev` to spin up the emulators
+   The Emulator UI is at http://localhost:4000; the functions are hosted on :5001.
+   Note: You have to kill and restart emulators when you change code; no hot reload =(
+3. Connect to emulators by enabling `functions.useEmulator('localhost', 5001)`
+
+## Debugging
+
+- Find local logs directly in the shell that ran `$ yarn dev`
+- Find deployed logs [here](https://console.firebase.google.com/project/mantic-markets/functions/logs?search=&&severity=DEBUG)
+
+## Deploying
+
+0. `$ firebase use prod` to switch to prod
+1. `$ yarn deploy` to push your changes live!
+   (Future TODO: auto-deploy functions on Git push)
+
+## Secrets management
+
+Secrets are strings that shouldn't be checked into Git (eg API keys, passwords). We store these using [environment config on Firebase Functions](https://firebase.google.com/docs/functions/config-env). Some useful workflows:
+
+- Set a secret: `$ firebase functions:config:set stripe.test_secret="THE-API-KEY"`
+- Preview all secrets: `$ firebase functions:config:get`
+- Cache for local dev:`$ firebase functions:config:get > .runtimeconfig.json`
diff --git a/functions/package.json b/functions/package.json
index a9763944..20991499 100644
--- a/functions/package.json
+++ b/functions/package.json
@@ -9,9 +9,6 @@
     "deploy": "firebase deploy --only functions",
     "logs": "firebase functions:log"
   },
-  "engines": {
-    "node": "14"
-  },
   "main": "lib/functions/src/index.js",
   "dependencies": {
     "fetch": "1.1.0",