diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index 7578d12f..81b049dc 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -103,20 +103,34 @@ See the section about [deployment][deployment] for more information.
 
 [deployment]: https://facebook.github.io/create-react-app/docs/deployment
 
-### `./tools/serve.py`
 
-WebBluetooth requires https. So to locally test the result of `yarn build`,
-run `./tools/serve.py` then point a web browser to <https://localhost:8443>
-(don't leave out https!).
+## Running the app locally
 
-Usually using `yarn start` is more convenient for local development, but this is
-particularly useful for testing changes on an Android device, for example. On
-remote devices, replace `localhost` with the hostname or IP address of the
-computer running the `./tools/serve.py` script.
+For most development work, running `yarn start` will suffice (see above).
+However, there are some features, like the service worker, that are disabled in
+this environment. To test the site as if it was deployed in production, we can
+serve up the output of `yarn build` instead.
 
-This server uses a self-signed certificate, so the browser will complain that
-the site is not secure. This warning can be ignored by clicking the *Advanced*
-button and then click the link to proceed to the site.
+This app uses "powerful web features" so requires a secure (https) connection.
+So for local testing without https, we need to follow
+<https://www.chromium.org/Home/chromium-security/deprecating-powerful-features-on-insecure-origins/#testing-powerful-features>.
+
+To serve the website, run:
+
+    yarn build
+    python3 -m http.server --directory build
+
+Note: the usual `npx serve` doesn't properly serve parts of the site so we use
+Python instead.
+
+Then at `chrome://flags/#unsafely-treat-insecure-origin-as-secure`, add:
+
+    http://localhost:8000
+
+and restart Chromium.
+
+The first link above also has info on how to use port forwarding to test on
+Android devices.
 
 ## Learn More
 
diff --git a/tools/serve.py b/tools/serve.py
deleted file mode 100755
index 7006d596..00000000
--- a/tools/serve.py
+++ /dev/null
@@ -1,34 +0,0 @@
-#!/usr/bin/env python3
-
-"""
-Serve local build with https for testing.
-
-This is useful, e.g. for Android (WebBluetooth doesn't work without https).
-
-Usage:
-
-    yarn build
-    ./tools/serve.py
-
-Browse to https://localhost:8443 on the local machine or
-https://<name-or-address>:8443 on a remote device.
-
-The browser will complain about the self-signed certificate, but this can be
-bypassed (click "Advanced" in browser).
-"""
-
-from http.server import HTTPServer, SimpleHTTPRequestHandler
-from pathlib import Path
-import os
-import ssl
-
-THIS_DIR = Path(__file__).parent
-TEST_CERT = (THIS_DIR / 'test.pem').absolute()
-BUILD_DIR = (THIS_DIR / '..' / 'build').absolute()
-
-# HTTPServer serves the current directory.
-os.chdir(BUILD_DIR)
-
-httpd = HTTPServer(('', 8443), SimpleHTTPRequestHandler)
-httpd.socket = ssl.wrap_socket(httpd.socket, certfile=TEST_CERT, server_side=True)
-httpd.serve_forever()
diff --git a/tools/test.pem b/tools/test.pem
deleted file mode 100644
index 85319120..00000000
--- a/tools/test.pem
+++ /dev/null
@@ -1,48 +0,0 @@
------BEGIN PRIVATE KEY-----
-MIIEvwIBADANBgkqhkiG9w0BAQEFAASCBKkwggSlAgEAAoIBAQDLpTko58nNd2cE
-q8MaB1Wv4xren/xiNomDwf44QK9jZGzvHqnXCKTQ0KsLxtZt7Ne6PU1WdIA3bf6/
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-i1rIWU10+ajud5ynlIS55IP2mxIi38GrtZ4NXpl9JxsRBZ16hiGneV7msCUCgYEA
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-AVMgdBof4DtucX+v+sLxuHAppA==
------END PRIVATE KEY-----
------BEGIN CERTIFICATE-----
-MIIDSzCCAjOgAwIBAgIUM9tef51ph3HVoJqF1h7ch5XmOQowDQYJKoZIhvcNAQEL
-BQAwNTELMAkGA1UEBhMCQVUxEzARBgNVBAgMClNvbWUtU3RhdGUxETAPBgNVBAoM
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-Qlai98tuzS49ekXd/dL6lXZi8z7c9Necj21mMgePKQ==
------END CERTIFICATE-----