diff --git a/changelog.d/20048.misc b/changelog.d/20048.misc
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@@ -0,0 +1 @@
+Document how to capture a JSON snapshot of a Grafana dashboard to aid in debugging.
diff --git a/contrib/grafana/README.md b/contrib/grafana/README.md
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--- a/contrib/grafana/README.md
+++ b/contrib/grafana/README.md
@@ -4,3 +4,60 @@
 1. Have your Prometheus scrape your Synapse. https://element-hq.github.io/synapse/latest/metrics-howto.html
 2. Import dashboard into Grafana. Download `synapse.json`. Import it to Grafana and select the correct Prometheus datasource. http://docs.grafana.org/reference/export_import/
 3. Set up required recording rules. [contrib/prometheus](../prometheus)
+
+
+## Sharing a JSON snapshot of a Grafana dashboard
+
+To aid in debugging, you can share the dashboard with others by creating a snapshot of
+the Grafana dashboard and exporting it as JSON. The snapshot will contain all of the
+current values of the metrics visible on the dashboard.
+
+**To capture the JSON snapshot:**
+
+ 1. Visit the Grafana dashboard in your browser
+ 1. Expand all of the sections on the dashboard and let all of the panels load in (the
+    snapshot only captures what's loaded on your page)
+ 1. Use the Grafana UI to capture the snapshot: **Share** (drop down arrow) -> **Share
+    Snapshot** -> **Publish Snapshot**
+       - If you run into `413` (`Content Too Large`) errors, you're probably just running
+         into the upload limit set on your reverse proxy (like nginx) in front of your
+         Grafana instance. Just increase it and try again.
+       - You may also run into `400` (`Bad Request`) which appear as `bad request data`
+         in the Grafana UI if the snapshot is larger than 100 MB. Grafana introduced a
+         [100 MB
+         limit](https://github.com/grafana/grafana/blob/555d6dde60b0f49acd453c7293b1cd518fda3592/pkg/web/binding.go#L13-L14)
+         as part of their [2026 June security
+         releases](https://github.com/grafana/grafana/pull/125789). There is no
+         workaround on this app limit, so you will have to reduce the time window,
+         number of panels shown, etc.
+ 1. Grab the snapshot ID from the link generated in the last step or find it from the
+    list of snapshots on https://localhost:3000/dashboard/snapshots
+ 1. To export the JSON, you have to use the [API for getting a
+    snapshot](https://grafana.com/docs/grafana/latest/developer-resources/api-reference/http-api/api-legacy/snapshot/#get-snapshot-by-key)
+    (update the snapshot ID in the command below):
+    ```shell
+    curl --request GET \
+      --header 'Content-Type: application/json' \
+      --output ~/Downloads/2026-08-16-synapse-myhomeserver.com.json \
+      http://admin:admin@localhost:3000/api/snapshots/nerimdSEDz530rM6CiwkEFi09A1841yF
+    ```
+ 1. If you're trying to upload to GitHub, keep in mind that GitHub has a 25MB limit for
+    attachments on issues. As an alternative, you could create a [GitHub
+    Gist](https://gist.github.com/). If the snapshot is too big to upload via the GitHub
+    UI, you can create a blank/empty gist and add it via git (gists are git repos).
+ 1. Once you have the JSON file, you can delete the snapshot from your Grafana instance
+    to free up space (from the snaphots page,
+    https://localhost:3000/dashboard/snapshots). The JSON file will still be valid and
+    can be shared with others.
+
+**To import the JSON snapshot into Grafana**, you have to use the [API for creating a snapshot](https://grafana.com/docs/grafana/latest/developer-resources/api-reference/http-api/snapshot/#create-new-snapshot) (passing in the whole JSON).
+
+ 1. Import example:
+    ```shell
+    cat ~/Downloads/2026-08-16-synapse-myhomeserver.com.json \
+      | jq '. += {"name": "2026-08-16-synapse-myhomeserver.com"}' \
+      | curl --request POST \
+          --header 'Content-Type: application/json' \
+          --data @- http://admin:admin@localhost:3000/api/snapshots
+    ```
+ 1. Then you can find the snapshot on https://localhost:3000/dashboard/snapshots to view it.