diff --git a/ChangeLog b/ChangeLog
index e90fefa97e..bc3f28ed03 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -81,6 +81,8 @@ Changes in version 0.2.1.6-alpha - 2008-09-xx
       servers.
     - Drop the requirement to have an open dir port for storing and serving
       v2 hidden service descriptors.
+    - Authorities now serve a /tor/dbg-stability.txt URL to help debug
+      WFU and MTBF calculations.
 
   o Code simplifications and refactoring:
     - Revise the connection_new functions so that a more typesafe variant
diff --git a/src/or/directory.c b/src/or/directory.c
index 8e4c6d4d3d..14c06b87fc 100644
--- a/src/or/directory.c
+++ b/src/or/directory.c
@@ -3004,6 +3004,21 @@ directory_handle_command_get(dir_connection_t *conn, const char *headers,
     goto done;
   }
 
+  if (!strcmp(url,"/tor/dbg-stability.txt")) {
+    const char *stability;
+    size_t len;
+    if (! authdir_mode_tests_reachability(options) ||
+        ! (stability = rep_hist_get_router_stability_doc(time(NULL)))) {
+      write_http_status_line(conn, 404, "Not found.");
+      goto done;
+    }
+
+    len = strlen(stability);
+    write_http_response_header(conn, len, 0, 0);
+    connection_write_to_buf(stability, len, TO_CONN(conn));
+    goto done;
+  }
+
 #if defined(EXPORTMALLINFO) && defined(HAVE_MALLOC_H) && defined(HAVE_MALLINFO)
 #define ADD_MALLINFO_LINE(x) do {                               \
     tor_snprintf(tmp, sizeof(tmp), "%s %d\n", #x, mi.x);        \
diff --git a/src/or/or.h b/src/or/or.h
index d21b30e5c6..f57dcfbd90 100644
--- a/src/or/or.h
+++ b/src/or/or.h
@@ -3841,6 +3841,7 @@ double rep_hist_get_stability(const char *id, time_t when);
 double rep_hist_get_weighted_fractional_uptime(const char *id, time_t when);
 long rep_hist_get_weighted_time_known(const char *id, time_t when);
 int rep_hist_have_measured_enough_stability(void);
+const char *rep_hist_get_router_stability_doc(time_t now);
 
 void rep_hist_note_used_port(time_t now, uint16_t port);
 smartlist_t *rep_hist_get_predicted_ports(time_t now);
diff --git a/src/or/rephist.c b/src/or/rephist.c
index c179b1180c..6262147cb8 100644
--- a/src/or/rephist.c
+++ b/src/or/rephist.c
@@ -765,6 +765,101 @@ rep_hist_record_mtbf_data(void)
   return -1;
 }
 
+/** DOCDOC */
+static char *
+rep_hist_format_router_status(or_history_t *hist, time_t now)
+{
+  char buf[1024];
+  char sor_buf[ISO_TIME_LEN+1];
+  char sod_buf[ISO_TIME_LEN+1];
+  double wfu;
+  double mtbf;
+  int up = 0, down = 0;
+
+  if (hist->start_of_run) {
+    format_iso_time(sor_buf, hist->start_of_run);
+    up = 1;
+  }
+  if (hist->start_of_downtime) {
+    format_iso_time(sor_buf, hist->start_of_downtime);
+    down = 1;
+  }
+
+  wfu = get_weighted_fractional_uptime(hist, now);
+  mtbf = get_stability(hist, now);
+  tor_snprintf(buf, sizeof(buf),
+               "%s%s%s"
+               "%s%s%s"
+               "wfu %0.3lf\n"
+               " weighted-time %lu\n"
+               " weighted-uptime %lu\n"
+               "mtbf %0.1lf\n"
+               " weighted-run-length %lu\n"
+               " total-run-weights %lf\n",
+               up?"uptime-started ":"", up?sor_buf:"", up?" UTC\n":"",
+               down?"downtime-started ":"", down?sod_buf:"", down?" UTC\n":"",
+               wfu,
+               hist->total_weighted_time,
+               hist->weighted_uptime,
+               mtbf,
+               hist->weighted_run_length,
+               hist->total_run_weights
+               );
+
+  return tor_strdup(buf);
+}
+
+/* DOCDOC */
+static char *last_stability_doc = NULL;
+static time_t built_last_stability_doc_at = 0;
+#define MAX_STABILITY_DOC_BUILD_RATE (3*60)
+
+/* DOCDOC */
+const char *
+rep_hist_get_router_stability_doc(time_t now)
+{
+  char *result;
+  smartlist_t *chunks;
+  if (built_last_stability_doc_at + MAX_STABILITY_DOC_BUILD_RATE > now)
+    return last_stability_doc;
+
+  if (!history_map)
+    return NULL;
+
+  tor_free(last_stability_doc);
+  chunks = smartlist_create();
+
+  DIGESTMAP_FOREACH(history_map, id, or_history_t *, hist) {
+    routerinfo_t *ri;
+    char dbuf[BASE64_DIGEST_LEN+1];
+    char header_buf[128];
+    char *info;
+    digest_to_base64(dbuf, id);
+    ri = router_get_by_digest(id);
+    if (ri) {
+      char *ip = tor_dup_ip(ri->addr);
+      tor_snprintf(header_buf, sizeof(header_buf), "router %s %s %s\n",
+                   dbuf, ri->nickname, ip);
+      tor_free(ip);
+    } else {
+      tor_snprintf(header_buf, sizeof(header_buf),
+                   "router %s {no descriptor}\n", dbuf);
+    }
+    smartlist_add(chunks, tor_strdup(header_buf));
+    info = rep_hist_format_router_status(hist, now);
+    if (info)
+      smartlist_add(chunks, info);
+  } DIGESTMAP_FOREACH_END;
+
+  result = smartlist_join_strings(chunks, "", 0, NULL);
+  SMARTLIST_FOREACH(chunks, char *, cp, tor_free(cp));
+  smartlist_free(chunks);
+
+  last_stability_doc = result;
+  built_last_stability_doc_at = time(NULL);
+  return result;
+}
+
 /** Helper: return the first j >= i such that !strcmpstart(sl[j], prefix) and
  * such that no line sl[k] with i <= k < j starts with "R ".  Return -1 if no
  * such line exists. */
@@ -1693,6 +1788,8 @@ rep_hist_free_all(void)
   digestmap_free(history_map, free_or_history);
   tor_free(read_array);
   tor_free(write_array);
+  tor_free(last_stability_doc);
+  built_last_stability_doc_at = 0;
   predicted_ports_free();
 }