diff --git a/src/gateway/public-gateway.mjs b/src/gateway/public-gateway.mjs
index 34aec4d..28661b8 100644
--- a/src/gateway/public-gateway.mjs
+++ b/src/gateway/public-gateway.mjs
@@ -171,7 +171,14 @@ async function serve(res, name, reqPath, baseHref) {
       case "s3": {
         const sub = subFolder(name);
         let base = r.s3; if (base.endsWith("/") && sub) base += sub + "/";
-        const key = base.endsWith("/") ? base + (reqPath === "/" ? "index.html" : reqPath.slice(1)) : base;
+        // Auto-index directory paths. S3 has no dir listing, so `/tools/`
+        // would 404 (NoSuchKey) without this — matches how nginx handles
+        // `try_files … /index.html` and how Ariadne's bnsd.js rewrites the
+        // same URLs client-side.
+        const rel = reqPath === "/" ? "index.html"
+                  : reqPath.endsWith("/") ? reqPath.slice(1) + "index.html"
+                  : reqPath.slice(1);
+        const key = base.endsWith("/") ? base + rel : base;
         const up = await aws.fetch(`${S3_ENDPOINT}/${key}`);
         const buf = Buffer.from(await up.arrayBuffer());
         let ct = up.headers.get("content-type"); if (!ct || ct === "application/octet-stream") ct = guess(key);