diff --git a/app/views/cards/_card.json.jbuilder b/app/views/cards/_card.json.jbuilder
index 75d3ebcf2..0ceb7e339 100644
--- a/app/views/cards/_card.json.jbuilder
+++ b/app/views/cards/_card.json.jbuilder
@@ -20,4 +20,5 @@ json.cache! card do
   json.has_more_assignees card.assignees.size > 5
 
   json.comments_url card_comments_url(card)
+  json.reactions_url card_reactions_url(card)
 end
diff --git a/docs/API.md b/docs/API.md
index bd4488127..f7bdacb30 100644
--- a/docs/API.md
+++ b/docs/API.md
@@ -553,7 +553,8 @@ __Response:__
       "created_at": "2025-12-05T19:36:35.401Z",
       "url": "http://fizzy.localhost:3006/897362094/users/03f5v9zjw7pz8717a4no1h8a7"
     },
-    "comments_url": "http://fizzy.localhost:3006/897362094/cards/4/comments"
+    "comments_url": "http://fizzy.localhost:3006/897362094/cards/4/comments",
+    "reactions_url": "http://fizzy.localhost:3006/897362094/cards/4/reactions"
   },
 ]
 ```
@@ -614,6 +615,7 @@ __Response:__
     "url": "http://fizzy.localhost:3006/897362094/users/03f5v9zjw7pz8717a4no1h8a7"
   },
   "comments_url": "http://fizzy.localhost:3006/897362094/cards/4/comments",
+  "reactions_url": "http://fizzy.localhost:3006/897362094/cards/4/reactions",
   "steps": [
     {
       "id": "03f8huu0sog76g3s975963b5e",
@@ -928,7 +930,66 @@ __Response:__
 
 Returns `204 No Content` on success.
 
-## Reactions
+## Card Reactions (Boosts)
+
+Card reactions (also called "boosts") let users add short responses directly to cards. These are limited to 16 characters.
+
+### `GET /:account_slug/cards/:card_number/reactions`
+
+Returns a list of reactions on a card.
+
+__Response:__
+
+```json
+[
+  {
+    "id": "03f5v9zo9qlcwwpyc0ascnikz",
+    "content": "👍",
+    "reacter": {
+      "id": "03f5v9zjw7pz8717a4no1h8a7",
+      "name": "David Heinemeier Hansson",
+      "role": "owner",
+      "active": true,
+      "email_address": "david@example.com",
+      "created_at": "2025-12-05T19:36:35.401Z",
+      "url": "http://fizzy.localhost:3006/897362094/users/03f5v9zjw7pz8717a4no1h8a7"
+    },
+    "url": "http://fizzy.localhost:3006/897362094/cards/3/reactions/03f5v9zo9qlcwwpyc0ascnikz"
+  }
+]
+```
+
+### `POST /:account_slug/cards/:card_number/reactions`
+
+Adds a reaction (boost) to a card.
+
+| Parameter | Type | Required | Description |
+|-----------|------|----------|-------------|
+| `content` | string | Yes | The reaction text (max 16 characters) |
+
+__Request:__
+
+```json
+{
+  "reaction": {
+    "content": "Great 👍"
+  }
+}
+```
+
+__Response:__
+
+Returns `201 Created` on success.
+
+### `DELETE /:account_slug/cards/:card_number/reactions/:reaction_id`
+
+Removes your reaction from a card. Only the reaction creator can remove their own reactions.
+
+__Response:__
+
+Returns `204 No Content` on success.
+
+## Comment Reactions
 
 Reactions are short (16-character max) responses to comments.
 
diff --git a/test/controllers/cards/comments_controller_test.rb b/test/controllers/cards/comments_controller_test.rb
index 0103a846f..26761d22e 100644
--- a/test/controllers/cards/comments_controller_test.rb
+++ b/test/controllers/cards/comments_controller_test.rb
@@ -79,6 +79,8 @@ class Cards::CommentsControllerTest < ActionDispatch::IntegrationTest
     assert_equal comment.id, @response.parsed_body["id"]
     assert_equal comment.card.id, @response.parsed_body.dig("card", "id")
     assert_equal card_url(comment.card.id), @response.parsed_body.dig("card", "url")
+    assert_equal card_comment_reactions_url(comment.card_id, comment.id), @response.parsed_body["reactions_url"]
+    assert_equal card_comment_url(comment.card_id, comment.id), @response.parsed_body["url"]
   end
 
   test "update as JSON" do
diff --git a/test/controllers/cards_controller_test.rb b/test/controllers/cards_controller_test.rb
index 8540912e6..dca7d986b 100644
--- a/test/controllers/cards_controller_test.rb
+++ b/test/controllers/cards_controller_test.rb
@@ -161,6 +161,8 @@ class CardsControllerTest < ActionDispatch::IntegrationTest
     assert_equal card.title, @response.parsed_body["title"]
     assert_equal card.closed?, @response.parsed_body["closed"]
     assert_equal 2, @response.parsed_body["steps"].size
+    assert_equal card_comments_url(card), @response.parsed_body["comments_url"]
+    assert_equal card_reactions_url(card), @response.parsed_body["reactions_url"]
   end
 
   test "create as JSON" do