diff --git a/bin/el/src/main.rs b/bin/el/src/main.rs
index b1b5395..e8d31be 100644
--- a/bin/el/src/main.rs
+++ b/bin/el/src/main.rs
@@ -3915,9 +3915,13 @@ fn dispatch_builtin(
                     method, path, _http_status, _req_latency_ms, request_id
                 ));
 
+                // Auto-detect HTML responses and serve with text/html content type.
+                let trimmed = response_body.trim_start();
+                let is_html = trimmed.starts_with("<!DOCTYPE") || trimmed.starts_with("<html") || trimmed.starts_with("<nav") || trimmed.starts_with("<div") || trimmed.starts_with("<main");
+                let response_header = if is_html { content_html } else { content_json };
                 let _ = request.respond(
                     tiny_http::Response::from_string(response_body)
-                        .with_header(content_json)
+                        .with_header(response_header)
                 );
             }
             stack.push(Value::Nil);