diff --git a/server/src/crate_server/readiness.gleam b/server/src/crate_server/readiness.gleam
index 9482027..0ba6204 100644
--- a/server/src/crate_server/readiness.gleam
+++ b/server/src/crate_server/readiness.gleam
@@ -17,6 +17,7 @@ import gleam/otp/actor
 import gleam/result
 import gleam/string
 import pog
+import wisp
 
 const cache_ttl_seconds = 5
 
@@ -72,6 +73,7 @@ type State {
     // a late reply from an abandoned attempt out of the current one.
     in_flight: Option(#(Int, Int)),
     next_generation: Int,
+    reported: Readiness,
     worker_replies: Subject(Msg),
   )
 }
@@ -142,6 +144,7 @@ pub fn cached(probe: fn() -> Readiness, now: fn() -> Int) -> Check {
         last: None,
         in_flight: None,
         next_generation: 0,
+        reported: Unknown(never_probed),
         worker_replies:,
       ))
       |> actor.selecting(selector)
@@ -161,6 +164,39 @@ pub fn status(check: Check) -> Readiness {
   check.run()
 }
 
+/// The line for a change of reported state, and nothing at all when the state
+/// has not moved: this gate is the one path that can take the whole site
+/// offline, so its transitions are logged while its probes are not.
+pub fn transition_line(from: Readiness, to: Readiness) -> Option(String) {
+  case from == to {
+    True -> None
+    False -> Some("readiness: " <> describe(from) <> " -> " <> describe(to))
+  }
+}
+
+fn describe(current: Readiness) -> String {
+  case current {
+    Ready -> "ready"
+    Unknown(reason) -> "unknown (" <> reason <> ")"
+    Down(reason) -> "down (" <> reason <> ")"
+  }
+}
+
+// Every answer funnels through here, so a flapping gate logs its transitions
+// rather than one line per probe.
+fn note(state: State, current: Readiness) -> State {
+  case transition_line(state.reported, current) {
+    None -> state
+    Some(line) -> {
+      case current {
+        Ready -> wisp.log_info(line)
+        Unknown(_) | Down(_) -> wisp.log_warning(line)
+      }
+      State(..state, reported: current)
+    }
+  }
+}
+
 fn handle(
   state: State,
   msg: Msg,
@@ -171,7 +207,7 @@ fn handle(
     Probe(reply) -> {
       let #(current, next) = respond(state, probe, now)
       process.send(reply, current)
-      actor.continue(next)
+      actor.continue(note(next, current))
     }
     ProbeResult(generation, current) ->
       actor.continue(accept(state, generation, current, now))
diff --git a/server/test/health_test.gleam b/server/test/health_test.gleam
index b1c8261..97bb391 100644
--- a/server/test/health_test.gleam
+++ b/server/test/health_test.gleam
@@ -10,6 +10,7 @@ import crate_server/router
 import gleam/erlang/process
 import gleam/http
 import gleam/list
+import gleam/option.{None, Some}
 import gleam/otp/actor
 import gleam/result
 import gleam/string
@@ -91,6 +92,23 @@ pub fn readyz_gates_on_the_wired_check_while_healthz_stays_up_test() {
   assert ready.status == 503
 }
 
+// An operator staring at 502s needs to know which of "missing table", "busy
+// pool" and "dead database" they are looking at, and needs it once per change
+// rather than once per probe.
+pub fn readiness_logs_state_changes_and_only_state_changes_test() {
+  let down = readiness.Down("known_users is missing")
+
+  assert readiness.transition_line(readiness.Ready, readiness.Ready) == None
+  assert readiness.transition_line(down, down) == None
+  assert readiness.transition_line(readiness.Ready, down)
+    == Some("readiness: ready -> down (known_users is missing)")
+  assert readiness.transition_line(
+      readiness.Unknown("connection unavailable"),
+      readiness.Ready,
+    )
+    == Some("readiness: unknown (connection unavailable) -> ready")
+}
+
 fn check_of(current: readiness.Readiness) -> readiness.Check {
   readiness.Check(fn() { current })
 }