diff --git a/src/amduatd.c b/src/amduatd.c
index 8d6da77..6f46944 100644
--- a/src/amduatd.c
+++ b/src/amduatd.c
@@ -283,6 +283,78 @@ static bool amduatd_http_send_json(int fd,
       fd, code, reason, "application/json", body, len, head_only);
 }
 
+static bool amduatd_http_req_wants_html(const amduatd_http_req_t *req) {
+  if (req == NULL) {
+    return false;
+  }
+  if (req->accept[0] == '\0') {
+    return false;
+  }
+  return strstr(req->accept, "text/html") != NULL;
+}
+
+static bool amduatd_http_send_not_found(int fd, const amduatd_http_req_t *req) {
+  if (amduatd_http_req_wants_html(req)) {
+    const char *path = (req != NULL && req->path[0] != '\0') ? req->path : "/";
+    const char *method =
+        (req != NULL && req->method[0] != '\0') ? req->method : "GET";
+    char html[4096];
+    int n = snprintf(
+        html,
+        sizeof(html),
+        "<!doctype html>\n"
+        "<html lang=\"en\">\n"
+        "<head>\n"
+        "  <meta charset=\"utf-8\" />\n"
+        "  <meta name=\"viewport\" content=\"width=device-width, initial-scale=1\" />\n"
+        "  <title>amduatd — Not Found</title>\n"
+        "  <style>\n"
+        "    :root{color-scheme:light dark;}\n"
+        "    body{font-family:ui-sans-serif,system-ui,-apple-system,Segoe UI,Roboto,Ubuntu,Cantarell,Noto Sans,Arial,sans-serif;"
+        "         margin:0;line-height:1.4;}\n"
+        "    .wrap{max-width:860px;margin:0 auto;padding:40px 20px;}\n"
+        "    .card{border:1px solid rgba(127,127,127,.35);border-radius:14px;padding:22px;"
+        "          background:rgba(127,127,127,.06);}\n"
+        "    h1{margin:0 0 6px;font-size:22px;}\n"
+        "    p{margin:8px 0;opacity:.9;}\n"
+        "    code{font-family:ui-monospace,SFMono-Regular,Menlo,Monaco,Consolas,Liberation Mono,monospace;"
+        "         font-size:13px;}\n"
+        "    ul{margin:10px 0 0;padding-left:18px;}\n"
+        "    a{color:inherit;}\n"
+        "    .muted{opacity:.75;}\n"
+        "  </style>\n"
+        "</head>\n"
+        "<body>\n"
+        "  <div class=\"wrap\">\n"
+        "    <div class=\"card\">\n"
+        "      <h1>404 — Not Found</h1>\n"
+        "      <p>amduatd didn’t recognize <code>%s %s</code>.</p>\n"
+        "      <p class=\"muted\">Try one of these:</p>\n"
+        "      <ul>\n"
+        "        <li><a href=\"/v1/meta\">/v1/meta</a></li>\n"
+        "        <li><a href=\"/v1/contract\">/v1/contract</a></li>\n"
+        "      </ul>\n"
+        "      <p class=\"muted\">Artifact bytes: <code>/v1/artifacts/&lt;ref&gt;</code></p>\n"
+        "    </div>\n"
+        "  </div>\n"
+        "</body>\n"
+        "</html>\n",
+        method,
+        path);
+    if (n <= 0 || (size_t)n >= sizeof(html)) {
+      return amduatd_http_send_text(fd, 404, "Not Found", "not found\n", false);
+    }
+    return amduatd_http_send_status(fd,
+                                   404,
+                                   "Not Found",
+                                   "text/html; charset=utf-8",
+                                   (const uint8_t *)html,
+                                   (size_t)n,
+                                   false);
+  }
+  return amduatd_http_send_text(fd, 404, "Not Found", "not found\n", false);
+}
+
 static const char *amduatd_query_param(const char *path,
                                        const char *key,
                                        char *out_value,
@@ -835,6 +907,7 @@ static bool amduatd_seed_api_contract(amduat_asl_store_t *store,
 
 static bool amduatd_handle_get_artifact(int fd,
                                         amduat_asl_store_t *store,
+                                        const amduatd_http_req_t *req,
                                         const char *path,
                                         bool head_only) {
   char no_query[1024];
@@ -850,8 +923,8 @@ static bool amduatd_handle_get_artifact(int fd,
   amduatd_path_without_query(path, no_query, sizeof(no_query));
 
   if (strncmp(no_query, "/v1/artifacts/", 14) != 0) {
-    return amduatd_http_send_text(fd, 404, "Not Found", "not found\n",
-                                 head_only);
+    (void)head_only;
+    return amduatd_http_send_not_found(fd, req);
   }
   ref_text = no_query + 14;
   if (ref_text[0] == '\0') {
@@ -880,8 +953,10 @@ static bool amduatd_handle_get_artifact(int fd,
   err = amduat_asl_store_get(store, ref, &artifact);
   free((void *)ref.digest.data);
   if (err == AMDUAT_ASL_STORE_ERR_NOT_FOUND) {
-    return amduatd_http_send_text(fd, 404, "Not Found", "not found\n",
-                                 head_only);
+    if (!head_only) {
+      return amduatd_http_send_not_found(fd, req);
+    }
+    return amduatd_http_send_text(fd, 404, "Not Found", "not found\n", true);
   }
   if (err != AMDUAT_ASL_STORE_OK) {
     amduat_asl_artifact_free(&artifact);
@@ -924,8 +999,9 @@ static bool amduatd_handle_get_artifact(int fd,
 
 static bool amduatd_handle_head_artifact(int fd,
                                          amduat_asl_store_t *store,
+                                         const amduatd_http_req_t *req,
                                          const char *path) {
-  return amduatd_handle_get_artifact(fd, store, path, true);
+  return amduatd_handle_get_artifact(fd, store, req, path, true);
 }
 
 static bool amduatd_handle_post_artifacts(int fd,
@@ -1453,14 +1529,14 @@ static bool amduatd_handle_conn(int fd,
   }
   if (strcmp(req.method, "GET") == 0 &&
       strncmp(no_query, "/v1/artifacts/", 14) == 0) {
-    return amduatd_handle_get_artifact(fd, store, req.path, false);
+    return amduatd_handle_get_artifact(fd, store, &req, req.path, false);
   }
   if (strcmp(req.method, "HEAD") == 0 &&
       strncmp(no_query, "/v1/artifacts/", 14) == 0) {
-    return amduatd_handle_head_artifact(fd, store, req.path);
+    return amduatd_handle_head_artifact(fd, store, &req, req.path);
   }
 
-  return amduatd_http_send_text(fd, 404, "Not Found", "not found\n", false);
+  return amduatd_http_send_not_found(fd, &req);
 }
 
 static void amduatd_print_usage(FILE *stream) {
