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+
+"health" ping
+=============
+
+This ping is intended to provide data about problems arise when submitting other pings.
+The ping is submitted at most once per hour. On shutdown an additional ping is submitted
+to avoid losing collected data.
+
+This ping is intended to be really small.
+The client id is submitted with this ping.
+
+.. code-block:: js
+
+    {
+      "type": "health", // type
+      ... common ping data
+      "clientId": <UUID>, // client id, e.g.
+                            // "c641eacf-c30c-4171-b403-f077724e848a"
+      "payload": {
+        "os": {
+            "name": <string>, // OS name
+            "version": <string> // OS version
+        },
+        "reason": <string>, // When ping was triggered, e.g. "immediate" or "shutdown".
+        "pingDiscardedForSize": {
+            "main": <number>, // Amount of occurrences for a specific ping type.
+            "core": <number>
+            ...
+        },
+        "sendFailure": {
+            "timeout": <number>, // Amount of occurrences for a specific failure.
+            "abort": <number>
+            ...
+        }
+      }
+    }
+
+Send behavior
+-------------
+
+``HealthPing.jsm`` tracks several problems:
+
+* The size of other assembled pings exceeds the ping limit.
+* Failures while sending other pings.
+
+After recording the data, a health ping will be sent:
+
+* immediately, with the reason ``immediate`` , if it is first ping in the session or it passed at least one hour from the previous submission.
+* after 1 hour minus the time passed from previous submission, with the reason ``delayed`` , if less than an hour passed from the previous submission.
+* on shutdown, with the reason ``shutdown`` using :doc:`../internals/pingsender`, if recorded data is not empty.
+
+Field details
+-------------
+
+reason
+~~~~~~
+The ``reason`` field contains the information about why the "health" ping was submitted. It presently supports three reasons:
+
+* immediate: The health ping was submitted immediately after recording a failure.
+* delayed: The health ping was submitted after a delay.
+* shutdown: The health ping was submitted on shutdown.
+
+pingDiscardedForSize
+~~~~~~~~~~~~~~~~~~~~
+The ``pingDiscardedForSize`` field contains the information about the top ten pings whose size exceeded the
+ping size limit (1 MB). This field lists the number of discarded pings per ping type.
+
+The ping type "<unknown>" is used to indicate that a pending pings size exceeded the limit. This is because we don't have the pending pings type available cheaply at the moment.
+
+This field is optional.
+
+sendFailure
+~~~~~~~~~~~
+The ``sendFailure`` field contains the information about pings, which had failures on sending.
+This field lists the number of failed pings per ping send failure type.
+
+The recorded failure types are:
+
+* "eOK" - No error.
+* "eRequest" - There was some error in the request before we started to service it.
+* "eUnreachable" - The remote server was unreachable.
+* "eChannelOpen" - The connection failed when we tried to open the channel.
+* "eRedirect" - The connection failed when being redirected.
+* "abort" - What XMLHttpRequest means by "abort" (see `MDN <https://developer.mozilla.org/en-US/docs/Web/Events/abort>`__)
+* "timeout" - What XMLHttpRequest means by "timeout" (see `MDN <https://developer.mozilla.org/en-US/docs/Web/Events/timeout>`__)
+
+This field is optional.
+
+.. note::
+
+    Although both ``pingDiscardedForSize`` and ``sendFailure`` fields are optional, the health ping will only
+    be submitted if one of this field not empty.