diff --git a/.github/changelog/add-jsonld-blurhash-term b/.github/changelog/add-jsonld-blurhash-term
new file mode 100644
index 0000000000..b1beb1fb9c
--- /dev/null
+++ b/.github/changelog/add-jsonld-blurhash-term
@@ -0,0 +1,4 @@
+Significance: patch
+Type: changed
+
+Add the `blurhash` term to the outbound JSON-LD `@context` so attachments that include a `blurhash` property are strictly correct JSON-LD, matching Mastodon's own context shape.
diff --git a/includes/activity/class-activity.php b/includes/activity/class-activity.php
index 28a5e30ae6..8f23a5932e 100644
--- a/includes/activity/class-activity.php
+++ b/includes/activity/class-activity.php
@@ -40,6 +40,7 @@ class Activity extends Base_Object {
 		array(
 			'toot'         => 'http://joinmastodon.org/ns#',
 			'QuoteRequest' => 'toot:QuoteRequest',
+			'blurhash'     => 'toot:blurhash',
 		),
 	);
 
diff --git a/includes/activity/class-base-object.php b/includes/activity/class-base-object.php
index 5668cd0ed8..8424ad33e0 100644
--- a/includes/activity/class-base-object.php
+++ b/includes/activity/class-base-object.php
@@ -162,6 +162,8 @@ class Base_Object extends Generic_Object {
 				'@id'   => 'gts:always',
 				'@type' => '@id',
 			),
+			'toot'              => 'http://joinmastodon.org/ns#',
+			'blurhash'          => 'toot:blurhash',
 		),
 	);
 
diff --git a/tests/phpunit/tests/includes/collection/class-test-outbox.php b/tests/phpunit/tests/includes/collection/class-test-outbox.php
index eefe982682..a53580ff7a 100644
--- a/tests/phpunit/tests/includes/collection/class-test-outbox.php
+++ b/tests/phpunit/tests/includes/collection/class-test-outbox.php
@@ -105,8 +105,8 @@ public function test_compare_objects() {
 	public function activity_object_provider() {
 		$home_url = \addcslashes( \home_url(), '/' );
 
-		$note1_json = '{"@context":["https:\/\/www.w3.org\/ns\/activitystreams",{"Hashtag":"as:Hashtag","sensitive":"as:sensitive","dcterms":"http:\/\/purl.org\/dc\/terms\/","gts":"https:\/\/gotosocial.org\/ns#","schema":"http:\/\/schema.org\/","exifData":"schema:exifData","PropertyValue":"schema:PropertyValue","interactionPolicy":{"@id":"gts:interactionPolicy","@type":"@id"},"canQuote":{"@id":"gts:canQuote","@type":"@id"},"canReply":{"@id":"gts:canReply","@type":"@id"},"canLike":{"@id":"gts:canLike","@type":"@id"},"canAnnounce":{"@id":"gts:canAnnounce","@type":"@id"},"automaticApproval":{"@id":"gts:automaticApproval","@type":"@id"},"manualApproval":{"@id":"gts:manualApproval","@type":"@id"},"always":{"@id":"gts:always","@type":"@id"}}],"actor":"http:\/\/example.org\/?author=1","id":"http:\/\/example.org\/?post_type=ap_outbox\u0026p=351","type":"Create","to":["https:\/\/www.w3.org\/ns\/activitystreams#Public"],"object":{"id":"https:\/\/example.com\/1","type":"Note","content":"\u003Cp\u003EThis is a note\u003C\/p\u003E","contentMap":{"en":"\u003Cp\u003EThis is a note\u003C\/p\u003E"},"tag":[],"to":["https:\/\/www.w3.org\/ns\/activitystreams#Public"],"mediaType":"text\/html"}}';
-		$note2_json = '{"@context":["https:\/\/www.w3.org\/ns\/activitystreams",{"Hashtag":"as:Hashtag","sensitive":"as:sensitive","dcterms":"http:\/\/purl.org\/dc\/terms\/","gts":"https:\/\/gotosocial.org\/ns#","schema":"http:\/\/schema.org\/","exifData":"schema:exifData","PropertyValue":"schema:PropertyValue","interactionPolicy":{"@id":"gts:interactionPolicy","@type":"@id"},"canQuote":{"@id":"gts:canQuote","@type":"@id"},"canReply":{"@id":"gts:canReply","@type":"@id"},"canLike":{"@id":"gts:canLike","@type":"@id"},"canAnnounce":{"@id":"gts:canAnnounce","@type":"@id"},"automaticApproval":{"@id":"gts:automaticApproval","@type":"@id"},"manualApproval":{"@id":"gts:manualApproval","@type":"@id"},"always":{"@id":"gts:always","@type":"@id"}}],"actor":"http:\/\/example.org\/?author=0","id":"http:\/\/example.org\/?post_type=ap_outbox\u0026p=352","type":"Create","to":["https:\/\/www.w3.org\/ns\/activitystreams#Public"],"object":{"id":"https:\/\/example.com\/2","type":"Note","content":"\u003Cp\u003EThis is another note\u003C\/p\u003E","contentMap":{"en":"\u003Cp\u003EThis is another note\u003C\/p\u003E"},"tag":[],"to":["https:\/\/www.w3.org\/ns\/activitystreams#Public"],"mediaType":"text\/html"}}';
+		$note1_json = '{"@context":["https:\/\/www.w3.org\/ns\/activitystreams",{"Hashtag":"as:Hashtag","sensitive":"as:sensitive","dcterms":"http:\/\/purl.org\/dc\/terms\/","gts":"https:\/\/gotosocial.org\/ns#","schema":"http:\/\/schema.org\/","exifData":"schema:exifData","PropertyValue":"schema:PropertyValue","interactionPolicy":{"@id":"gts:interactionPolicy","@type":"@id"},"canQuote":{"@id":"gts:canQuote","@type":"@id"},"canReply":{"@id":"gts:canReply","@type":"@id"},"canLike":{"@id":"gts:canLike","@type":"@id"},"canAnnounce":{"@id":"gts:canAnnounce","@type":"@id"},"automaticApproval":{"@id":"gts:automaticApproval","@type":"@id"},"manualApproval":{"@id":"gts:manualApproval","@type":"@id"},"always":{"@id":"gts:always","@type":"@id"},"toot":"http:\/\/joinmastodon.org\/ns#","blurhash":"toot:blurhash"}],"actor":"http:\/\/example.org\/?author=1","id":"http:\/\/example.org\/?post_type=ap_outbox\u0026p=351","type":"Create","to":["https:\/\/www.w3.org\/ns\/activitystreams#Public"],"object":{"id":"https:\/\/example.com\/1","type":"Note","content":"\u003Cp\u003EThis is a note\u003C\/p\u003E","contentMap":{"en":"\u003Cp\u003EThis is a note\u003C\/p\u003E"},"tag":[],"to":["https:\/\/www.w3.org\/ns\/activitystreams#Public"],"mediaType":"text\/html"}}';
+		$note2_json = '{"@context":["https:\/\/www.w3.org\/ns\/activitystreams",{"Hashtag":"as:Hashtag","sensitive":"as:sensitive","dcterms":"http:\/\/purl.org\/dc\/terms\/","gts":"https:\/\/gotosocial.org\/ns#","schema":"http:\/\/schema.org\/","exifData":"schema:exifData","PropertyValue":"schema:PropertyValue","interactionPolicy":{"@id":"gts:interactionPolicy","@type":"@id"},"canQuote":{"@id":"gts:canQuote","@type":"@id"},"canReply":{"@id":"gts:canReply","@type":"@id"},"canLike":{"@id":"gts:canLike","@type":"@id"},"canAnnounce":{"@id":"gts:canAnnounce","@type":"@id"},"automaticApproval":{"@id":"gts:automaticApproval","@type":"@id"},"manualApproval":{"@id":"gts:manualApproval","@type":"@id"},"always":{"@id":"gts:always","@type":"@id"},"toot":"http:\/\/joinmastodon.org\/ns#","blurhash":"toot:blurhash"}],"actor":"http:\/\/example.org\/?author=0","id":"http:\/\/example.org\/?post_type=ap_outbox\u0026p=352","type":"Create","to":["https:\/\/www.w3.org\/ns\/activitystreams#Public"],"object":{"id":"https:\/\/example.com\/2","type":"Note","content":"\u003Cp\u003EThis is another note\u003C\/p\u003E","contentMap":{"en":"\u003Cp\u003EThis is another note\u003C\/p\u003E"},"tag":[],"to":["https:\/\/www.w3.org\/ns\/activitystreams#Public"],"mediaType":"text\/html"}}';
 		$event_json = '{"@context":["https:\/\/schema.org\/","https:\/\/www.w3.org\/ns\/activitystreams",{"pt":"https:\/\/joinpeertube.org\/ns#","mz":"https:\/\/joinmobilizon.org\/ns#","status":"http:\/\/www.w3.org\/2002\/12\/cal\/ical#status","commentsEnabled":"pt:commentsEnabled","isOnline":"mz:isOnline","timezone":"mz:timezone","participantCount":"mz:participantCount","anonymousParticipationEnabled":"mz:anonymousParticipationEnabled","joinMode":{"@id":"mz:joinMode","@type":"mz:joinModeType"},"externalParticipationUrl":{"@id":"mz:externalParticipationUrl","@type":"schema:URL"},"repliesModerationOption":{"@id":"mz:repliesModerationOption","@type":"@vocab"},"contacts":{"@id":"mz:contacts","@type":"@id"}}],"actor":"http:\/\/example.org\/?author=1","id":"http:\/\/example.org\/?post_type=ap_outbox\u0026p=353","type":"Create","to":["https:\/\/www.w3.org\/ns\/activitystreams#Public"],"object":{"id":"https:\/\/example.com\/3","type":"Event","content":"\u003Cp\u003EYou should not miss this Event!\u003C\/p\u003E","contentMap":{"en":"\u003Cp\u003EYou should not miss this Event!\u003C\/p\u003E"},"name":"WP Test Event","nameMap":{"en":"WP Test Event"},"endTime":"2030-02-29T17:00:00+01:00","location":[{"id":"https:\/\/example.com\/place\/1","type":"Place","attributedTo":"https:\/\/wp-test.event-federation.eu\/@test","name":"Fediverse Place","address":{"type":"PostalAddress","addressCountry":"FediCountry","addressLocality":"FediTown","postalCode":"1337","streetAddress":"FediStreet"}},{"type":"VirtualLocation","url":"https:\/\/example.com\/VirtualMeetingRoom"}],"startTime":"2030-02-29T16:00:00+01:00","to":["https:\/\/www.w3.org\/ns\/activitystreams#Public"],"mediaType":"text\/html","tag":[],"timezone":"Europe\/Vienna","category":"MOVEMENTS_POLITICS","joinMode":"external"}}';
 		return array(
 			array(