diff --git a/docs/functions/clean-html-urls.ts b/docs/functions/clean-html-urls.ts
new file mode 100644
index 0000000000..eadd654a68
--- /dev/null
+++ b/docs/functions/clean-html-urls.ts
@@ -0,0 +1,27 @@
+// Redirect legacy *.html URLs to their extensionless equivalents. Runs as an
+// edge function because a wildcard _redirects rule can't force a redirect
+// away from a file that physically exists at the "from" path.
+import { Context } from "@netlify/edge-functions";
+
+const excluded: Set<string> = new Set([
+  "/netlify-forms.html",
+  "/docs/kubernetes-admission-control.html",
+]);
+
+export default async (
+  request: Request,
+  context: Context,
+): Promise<Response | undefined> => {
+  const url: URL = new URL(request.url);
+  const pathname: string = url.pathname;
+
+  if (!pathname.endsWith(".html") || excluded.has(pathname)) {
+    return undefined;
+  }
+
+  url.pathname = pathname === "/index.html"
+    ? "/"
+    : pathname.slice(0, -".html".length);
+
+  return Response.redirect(url.toString(), 301);
+};
diff --git a/docs/src/pages/ecosystem/index.jsx b/docs/src/pages/ecosystem/index.jsx
index 13422f43db..0722a67bf7 100644
--- a/docs/src/pages/ecosystem/index.jsx
+++ b/docs/src/pages/ecosystem/index.jsx
@@ -1,6 +1,7 @@
 import React, { useState } from "react";
 
 import Link from "@docusaurus/Link";
+import useBaseUrl from "@docusaurus/useBaseUrl";
 import Heading from "@theme/Heading";
 import Layout from "@theme/Layout";
 
@@ -94,7 +95,7 @@ const EcosystemIndex = (props) => {
                   return (
                     <a
                       key={lang.id}
-                      href={`./ecosystem/by-language/${lang.id}`}
+                      href={useBaseUrl(`/ecosystem/by-language/${lang.id}`)}
                       className={styles.languageLink}
                     >
                       <img
@@ -128,7 +129,8 @@ const EcosystemIndex = (props) => {
                   <ul>
                     {featuresInCategory.map((feature) => (
                       <li key={feature.id}>
-                        <a href={`./ecosystem/by-feature/${feature.id}`}>{feature.title}</a> – {feature.description}
+                        <a href={useBaseUrl(`/ecosystem/by-feature/${feature.id}`)}>{feature.title}</a> –{" "}
+                        {feature.description}
                       </li>
                     ))}
                   </ul>
diff --git a/netlify.toml b/netlify.toml
index 7d1974c0f0..e76b4ff3a0 100644
--- a/netlify.toml
+++ b/netlify.toml
@@ -27,6 +27,11 @@ function = "badge"
 path = "/docs/*"
 function = "version-redirect"
 
+# Canonicalize legacy .html URLs onto their clean-path equivalents.
+[[edge_functions]]
+path = "/*"
+function = "clean-html-urls"
+
 # function to process form notifications from netlify forms and send them to slack
 [[edge_functions]]
 path = "/api/feedback"