diff --git a/docs/src/SUMMARY.md b/docs/src/SUMMARY.md
index 323b2cfb..d2ea5b3f 100644
--- a/docs/src/SUMMARY.md
+++ b/docs/src/SUMMARY.md
@@ -12,4 +12,5 @@
 
 # Others
 
-- [Compatibility Chart](./others/00-compatibility-chart.md)
+- [Compatibility Chart](./others/compatibility-chart.md)
+- [JSON Feed Extension](./others/json-feed-extension.md)
diff --git a/docs/src/others/00-compatibility-chart.md b/docs/src/others/compatibility-chart.md
similarity index 100%
rename from docs/src/others/00-compatibility-chart.md
rename to docs/src/others/compatibility-chart.md
diff --git a/docs/src/others/json-feed-extension.md b/docs/src/others/json-feed-extension.md
new file mode 100644
index 00000000..e3b63895
--- /dev/null
+++ b/docs/src/others/json-feed-extension.md
@@ -0,0 +1,20 @@
+# Hatsu JSON Feed Extension
+
+To allow you to customize your postings, Hatsu defines a JSON Feed extension that uses the `_hatsu` key.
+
+All extension keys for the Hatsu JSON Feed Extension are optional.
+
+> Note: everything here is experimental. It is always subject to breaking changes and does not follow semver.
+
+## Top-level
+
+The following applies to the [Top-level JSON Feed](https://www.jsonfeed.org/version/1.1/#top-level-a-name-top-level-a).
+
+- `about` (optional but strongly recommended, string) is the URL used to introduce this extension to humans. should be [https://github.com/importantimport/hatsu/issues/1](https://github.com/importantimport/hatsu/issues/1) .
+- `banner_image` (optional, string) is the URL of the banner image for the website in hatsu.
+
+## items
+
+The following applies to the [JSON Feed Item](https://www.jsonfeed.org/version/1.1/#items-a-name-items-a).
+
+- `about` (optional but strongly recommended, string) is the URL used to introduce this extension to humans. should be `https://github.com/importantimport/hatsu/issues/1`.