diff --git a/content/docs/build/server-api.mdx b/content/docs/build/server-api.mdx
index e367225..c66e63d 100644
--- a/content/docs/build/server-api.mdx
+++ b/content/docs/build/server-api.mdx
@@ -75,6 +75,7 @@ Sending is `chat:send` over the socket. There's no POST here.
 | POST | `/api/uploads/avatar` | Bearer | multipart |
 | DELETE | `/api/uploads/avatar` | Bearer | |
 | POST | `/api/uploads/group-icon` | Bearer | multipart `file`, a group's picture. Returns `fileId` for `dm:group:update` and doesn't change your avatar |
+| POST | `/api/uploads/webhook-avatar` | Bearer | multipart `file`, a webhook's avatar. Needs Manage webhooks. Returns `fileId` for the webhook's `avatar_file_id` and doesn't change your avatar |
 | GET | `/api/uploads/files/:fileId` | — | `?thumb=1` for the thumbnail, `?download=1` for an attachment header |
 
 ### Server
diff --git a/content/docs/build/webhooks.mdx b/content/docs/build/webhooks.mdx
index 67ddcdd..04e60e9 100644
--- a/content/docs/build/webhooks.mdx
+++ b/content/docs/build/webhooks.mdx
@@ -148,6 +148,8 @@ original URL afterwards changes nothing in Gryt.
 - Private and local addresses are refused, and so is a chain of more than 5
   redirects
 - The same URL used twice in a message is downloaded once
+- `avatar_url` is resized to 256 px, the same as any other avatar. Card pictures
+  keep their size
 
 A picture that fails doesn't stop the message. It posts without that picture,
 and the reply lists what went wrong under `warnings`. Because of the downloads,
diff --git a/src/components/webhooks/openapi.json b/src/components/webhooks/openapi.json
index 7b5ffe5..51ac5d2 100644
--- a/src/components/webhooks/openapi.json
+++ b/src/components/webhooks/openapi.json
@@ -42,7 +42,7 @@
             "type": "string"
           },
           "avatar_url": {
-            "description": "Posts with this picture instead of the webhook's. Fetched once and stored, same as card images.",
+            "description": "Posts with this picture instead of the webhook's. Downloaded once and resized to 256 px, like any other avatar.",
             "type": "string",
             "maxLength": 2048,
             "format": "uri"