diff --git a/backend/config/test.exs b/backend/config/test.exs
index d533a8f..c45f422 100644
--- a/backend/config/test.exs
+++ b/backend/config/test.exs
@@ -18,3 +18,5 @@ config :backend, Backend.Repo,
   pool: Ecto.Adapters.SQL.Sandbox
 
 config :appsignal, :config, active: false
+
+config :backend, :crawler, status_count_limit: 5
diff --git a/backend/lib/backend/crawler/crawlers/misskey.ex b/backend/lib/backend/crawler/crawlers/misskey.ex
index 9ee734b..092d48f 100644
--- a/backend/lib/backend/crawler/crawlers/misskey.ex
+++ b/backend/lib/backend/crawler/crawlers/misskey.ex
@@ -98,7 +98,7 @@ defmodule Backend.Crawler.Crawlers.Misskey do
     endpoint = "https://#{domain}/api/notes/local-timeline"
 
     params = %{
-      limit: 20
+      limit: 100
     }
 
     params =
@@ -110,7 +110,7 @@ defmodule Backend.Crawler.Crawlers.Misskey do
 
     Logger.debug("Crawling #{endpoint} with untilId=#{until_id}")
 
-    statuses = http_client().post_and_decode!(endpoint, Jason.encode!(params))
+    statuses = http_client().post_and_decode!(endpoint, params)
 
     filtered_statuses =
       statuses
diff --git a/backend/lib/backend/http.ex b/backend/lib/backend/http.ex
index 876de0f..7ad7db4 100644
--- a/backend/lib/backend/http.ex
+++ b/backend/lib/backend/http.ex
@@ -23,7 +23,7 @@ defmodule Backend.Http do
          ) do
       {:ok, %HTTPoison.Response{body: body, status_code: status_code}}
       when status_code >= 200 and status_code <= 299 ->
-        Jason.decode(body)
+        decode_body(body)
 
       {:ok, %HTTPoison.Response{body: body, status_code: status_code}} ->
         if not is_nil(default) do
@@ -50,11 +50,18 @@ defmodule Backend.Http do
     end
   end
 
+  @doc """
+  POSTs to the given URL with the given body and returns the JSON-decoded response.
+  The given body is JSON-encoded before sending.
+  """
   @impl true
-  def post_and_decode(url, body \\ nil) do
-    case HTTPoison.post(url, body, [{"User-Agent", get_config(:user_agent)}]) do
+  def post_and_decode(url, body \\ %{}) do
+    case HTTPoison.post(url, Jason.encode!(body), [
+           {"User-Agent", get_config(:user_agent)},
+           {"Content-Type", "application/json"}
+         ]) do
       {:ok, %HTTPoison.Response{body: body}} ->
-        Jason.decode(body)
+        decode_body(body)
 
       {:error, %HTTPoison.Error{} = error} ->
         {:error, %Error{message: HTTPoison.Error.message(error)}}
@@ -62,10 +69,25 @@ defmodule Backend.Http do
   end
 
   @impl true
-  def post_and_decode!(url, body \\ nil) do
+  def post_and_decode!(url, body \\ %{}) do
     case post_and_decode(url, body) do
-      {:ok, decoded} -> decoded
-      {:error, error} -> raise error
+      {:ok, decoded} ->
+        decoded
+
+      {:error, error} ->
+        raise error
+    end
+  end
+
+  defp decode_body(body) do
+    with {:ok, decoded} <- Jason.decode(body) do
+      if is_map(decoded) and (Map.has_key?(decoded, "errors") or Map.has_key?(decoded, "error")) do
+        {:error, %Error{message: "API error: " <> body}}
+      else
+        {:ok, decoded}
+      end
+    else
+      {:error, error} -> {:error, error}
     end
   end
 end
diff --git a/backend/test/backend/crawler/crawlers/misskey_test.exs b/backend/test/backend/crawler/crawlers/misskey_test.exs
new file mode 100644
index 0000000..0a971b8
--- /dev/null
+++ b/backend/test/backend/crawler/crawlers/misskey_test.exs
@@ -0,0 +1,68 @@
+defmodule Backend.Crawler.Crawlers.MisskeyTest do
+  use Backend.DataCase
+
+  alias Backend.Crawler.Crawlers.Misskey
+  alias Backend.Crawler.ApiCrawler
+  import Mox
+
+  setup :verify_on_exit!
+
+  describe "is_instance_type?/2" do
+    test "returns true for misskey instance" do
+      expect(HttpMock, :post_and_decode, fn "https://example.com/api/meta" ->
+        {:ok, TestHelpers.load_json("misskey/meta.json")}
+      end)
+
+      assert Misskey.is_instance_type?("example.com", nil)
+    end
+  end
+
+  describe "crawl/2" do
+    test "does nothing for small instances" do
+      expect(HttpMock, :post_and_decode, fn "https://example.com/api/stats" ->
+        stats =
+          TestHelpers.load_json("misskey/stats.json") |> Map.merge(%{"originalUsersCount" => 1})
+
+        {:ok, stats}
+      end)
+
+      result = Misskey.crawl("example.com", ApiCrawler.get_default())
+
+      assert result == ApiCrawler.get_default() |> Map.merge(%{type: :misskey, user_count: 1})
+    end
+
+    test "crawls large instances" do
+      expect(HttpMock, :post_and_decode, fn "https://example.com/api/stats" ->
+        {:ok, TestHelpers.load_json("misskey/stats.json")}
+      end)
+
+      expect(HttpMock, :post_and_decode, fn "https://example.com/api/meta" ->
+        {:ok, TestHelpers.load_json("misskey/meta.json")}
+      end)
+
+      expect(HttpMock, :get_and_decode, fn "https://example.com/api/v1/instance/peers" ->
+        {:ok, TestHelpers.load_json("misskey/peers.json")}
+      end)
+
+      # status_count_limit is 5, response has 1 post per page, so we expect 5 requests
+      expect(HttpMock, :post_and_decode!, 5, fn "https://example.com/api/notes/local-timeline",
+                                                %{limit: 100} ->
+        TestHelpers.load_json("misskey/notes.json")
+      end)
+
+      result = Misskey.crawl("example.com", ApiCrawler.get_default())
+
+      assert result == %{
+               description: "some description",
+               federation_restrictions: [],
+               instance_type: :misskey,
+               interactions: %{},
+               peers: ["other.com"],
+               status_count: 20,
+               statuses_seen: 5,
+               user_count: 20,
+               version: "13.12.2"
+             }
+    end
+  end
+end
diff --git a/backend/test/backend/crawler/crawlers/nodeinfo_test.exs b/backend/test/backend/crawler/crawlers/nodeinfo_test.exs
index 92fe547..a6ca1f5 100644
--- a/backend/test/backend/crawler/crawlers/nodeinfo_test.exs
+++ b/backend/test/backend/crawler/crawlers/nodeinfo_test.exs
@@ -1,5 +1,5 @@
 defmodule Backend.Crawler.Crawlers.NodeinfoTest do
-  use Backend.DataCase
+  use ExUnit.Case
 
   alias Backend.Crawler.Crawlers.Nodeinfo
   import Mox
@@ -134,5 +134,25 @@ defmodule Backend.Crawler.Crawlers.NodeinfoTest do
                peers: []
              }
     end
+
+    test "handles non-200 response" do
+      expect(HttpMock, :get_and_decode, fn "https://mastodon.social/.well-known/nodeinfo" ->
+        {:error, %Backend.HttpBehaviour.Error{status_code: 401}}
+      end)
+
+      result = Nodeinfo.crawl("mastodon.social", %{})
+
+      assert result == %{
+               description: nil,
+               user_count: nil,
+               status_count: nil,
+               statuses_seen: 0,
+               instance_type: nil,
+               version: nil,
+               federation_restrictions: [],
+               interactions: %{},
+               peers: []
+             }
+    end
   end
 end
diff --git a/backend/test/support/data/json/misskey/meta.json b/backend/test/support/data/json/misskey/meta.json
new file mode 100644
index 0000000..7e05d14
--- /dev/null
+++ b/backend/test/support/data/json/misskey/meta.json
@@ -0,0 +1,170 @@
+{
+  "maintainerName": "MisskeyHQ",
+  "maintainerEmail": "https://go.misskey.io/support",
+  "version": "13.12.2",
+  "name": "Misskey.io",
+  "uri": "https://misskey.io",
+  "description": "some description",
+  "langs": ["ja", "en", "zh", "ko", "fr", "de"],
+  "tosUrl": "http://go.misskey.io/tos",
+  "repositoryUrl": "https://github.com/syuilo/misskey",
+  "feedbackUrl": "https://github.com/syuilo/misskey/issues/new",
+  "disableRegistration": false,
+  "emailRequiredForSignup": true,
+  "enableHcaptcha": false,
+  "hcaptchaSiteKey": "95d75440-7e37-4419-a693-8f52c377f1c5",
+  "enableRecaptcha": false,
+  "recaptchaSiteKey": "6LfW8qQUAAAAAI_1WMThmcj6zO39laasAoEJHfFF",
+  "enableTurnstile": true,
+  "turnstileSiteKey": "0x4AAAAAAACJmZyh3LCvo-uf",
+  "swPublickey": "BHqCPVsCM8pMUo26Fenl6fuLPfuqQTNeo2Rpvt6KFxFEKznKAXZBHI2nk1aAanlJ1Me_PSr-MVkW3ho4RaYmZpk",
+  "themeColor": "#86b300",
+  "mascotImageUrl": "/assets/ai.png",
+  "bannerUrl": "https://s3.arkjp.net/misskey/65b25d3c-2ae4-474f-b1c0-050c8c8962e1.jpg",
+  "errorImageUrl": "https://s3.arkjp.net/misskey/94aab3c5-0b26-42a7-9fa9-83a69d7253cd.png",
+  "iconUrl": "https://s3.arkjp.net/misskey/webpublic-0c66b1ca-b8c0-4eaa-9827-47674f4a1580.png",
+  "backgroundImageUrl": "https://s3.arkjp.net/misskey/e23f6837-c477-4f40-bbc7-b8a06e3bc1cc.jpg",
+  "logoImageUrl": "https://s3.arkjp.net/misskey/31240fa8-98fa-4750-bfd4-767753d1c48d.png",
+  "maxNoteTextLength": 3000,
+  "defaultLightTheme": null,
+  "defaultDarkTheme": null,
+  "ads": [
+    {
+      "id": "8riz9d7mt0",
+      "url": "http://go.misskey.io/nextdns",
+      "place": "horizontal",
+      "ratio": 3,
+      "imageUrl": "https://s3.arkjp.net/misskey/03992473-790d-4e50-9f70-f12ed1a5aabb.png"
+    },
+    {
+      "id": "8rkte84ghf",
+      "url": "https://go.misskey.io/vultr",
+      "place": "horizontal",
+      "ratio": 3,
+      "imageUrl": "https://s3.arkjp.net/misskey/fa1421c3-fabc-4dbc-a688-52dfb7491660.webp"
+    },
+    {
+      "id": "97crkngnt7",
+      "url": "https://go.misskey.io/ads",
+      "place": "horizontal",
+      "ratio": 1,
+      "imageUrl": "https://s3.arkjp.net/misskey/d85e0e31-522b-4779-8479-b7acb65c86dc.png"
+    },
+    {
+      "id": "97crxz63al",
+      "url": "https://go.misskey.io/ads",
+      "place": "horizontal",
+      "ratio": 1,
+      "imageUrl": "https://s3.arkjp.net/misskey/d73e0b21-5910-42f7-9f1b-6983026ee1db.png"
+    },
+    {
+      "id": "97cspskh3f",
+      "url": "https://go.misskey.io/ads",
+      "place": "horizontal",
+      "ratio": 1,
+      "imageUrl": "https://s3.arkjp.net/misskey/36fe91e6-5d11-4f12-8bc8-426ab0ebd885.png"
+    },
+    {
+      "id": "9clihjru6p",
+      "url": "https://go.misskey.io/maZC",
+      "place": "horizontal",
+      "ratio": 40,
+      "imageUrl": "https://s3.arkjp.net/misskey/ee74935a-a1ec-4385-bb36-2377387118b8.png"
+    },
+    {
+      "id": "9e5idmskrv",
+      "url": "https://go.misskey.io/LfNP",
+      "place": "horizontal-big",
+      "ratio": 20,
+      "imageUrl": "https://s3.arkjp.net/misskey/4e03fca5-b25f-4950-974a-313a7d958b6d.png"
+    },
+    {
+      "id": "9eo9im87s6",
+      "url": "https://go.misskey.io/jHVi",
+      "place": "horizontal-big",
+      "ratio": 40,
+      "imageUrl": "https://s3.arkjp.net/misskey/7e903951-e7e1-4277-badf-0ea5bc9ab07a.png"
+    },
+    {
+      "id": "9f00tkswhg",
+      "url": "https://go.misskey.io/wD6e",
+      "place": "horizontal-big",
+      "ratio": 20,
+      "imageUrl": "https://s3.arkjp.net/misskey/015a3335-b21e-4897-a958-d6879b2a82f1.png"
+    },
+    {
+      "id": "9f3stos3s7",
+      "url": "https://go.misskey.io/iMxB",
+      "place": "horizontal-big",
+      "ratio": 40,
+      "imageUrl": "https://s3.arkjp.net/misskey/098ceb69-8238-4c3c-8f99-f9752294cb96.png"
+    },
+    {
+      "id": "9fgxdm8mpd",
+      "url": "https://go.misskey.io/dwRP",
+      "place": "horizontal-big",
+      "ratio": 60,
+      "imageUrl": "https://s3.arkjp.net/misskey/c4650ddc-687e-46c0-932a-c1f5ca8c9f83.png"
+    },
+    {
+      "id": "9fhdbdyevw",
+      "url": "https://go.misskey.io/pwYv",
+      "place": "horizontal",
+      "ratio": 40,
+      "imageUrl": "https://s3.arkjp.net/misskey/e2f6c692-0d16-4fe9-90c4-25eac1b31731.png"
+    },
+    {
+      "id": "9fgjjfdr3s",
+      "url": "https://go.misskey.io/VwEm",
+      "place": "horizontal-big",
+      "ratio": 60,
+      "imageUrl": "https://s3.arkjp.net/misskey/951bda53-3707-480e-ab5a-0000ca9c7578.png"
+    },
+    {
+      "id": "9fnpd9tsgs",
+      "url": "https://go.misskey.io/QwId",
+      "place": "horizontal-big",
+      "ratio": 80,
+      "imageUrl": "https://s3.arkjp.net/misskey/261f7323-7a5e-4734-92bc-6ad69a4226df.jpg"
+    },
+    {
+      "id": "9fmru4ok7f",
+      "url": "https://go.misskey.io/pwYv",
+      "place": "horizontal-big",
+      "ratio": 20,
+      "imageUrl": "https://s3.arkjp.net/misskey/563a709e-6d5e-4952-9cb5-ac6897f80990.png"
+    },
+    {
+      "id": "9ew2fhwyfc",
+      "url": "https://go.misskey.io/sjxJ",
+      "place": "horizontal-big",
+      "ratio": 60,
+      "imageUrl": "https://s3.arkjp.net/misskey/8dff6f2d-444f-459f-80ff-02cad454be91.png"
+    }
+  ],
+  "enableEmail": true,
+  "enableServiceWorker": true,
+  "translatorAvailable": true,
+  "serverRules": [],
+  "policies": {
+    "gtlAvailable": true,
+    "ltlAvailable": true,
+    "canPublicNote": true,
+    "canInvite": false,
+    "canManageCustomEmojis": false,
+    "canSearchNotes": false,
+    "canHideAds": false,
+    "driveCapacityMb": 10240,
+    "alwaysMarkNsfw": false,
+    "pinLimit": 3,
+    "antennaLimit": 5,
+    "wordMuteLimit": 200,
+    "webhookLimit": 3,
+    "clipLimit": 10,
+    "noteEachClipsLimit": 50,
+    "userListLimit": 5,
+    "userEachUserListsLimit": 20,
+    "rateLimitFactor": 2
+  },
+  "mediaProxy": "https://nos3.arkjp.net"
+}
diff --git a/backend/test/support/data/json/misskey/notes.json b/backend/test/support/data/json/misskey/notes.json
new file mode 100644
index 0000000..f61387a
--- /dev/null
+++ b/backend/test/support/data/json/misskey/notes.json
@@ -0,0 +1,33 @@
+[
+  {
+    "id": "9ftvwz5kx8no7aeb",
+    "createdAt": "2023-06-10T18:18:57.656Z",
+    "userId": "9badbj0vp9",
+    "user": {
+      "id": "9badbj0vp9",
+      "name": "Some Name",
+      "username": "username",
+      "host": null,
+      "avatarUrl": "https://example.com/image.png",
+      "avatarBlurhash": "foobar",
+      "avatarColor": null,
+      "speakAsCat": true,
+      "emojis": [],
+      "onlineStatus": "online",
+      "driveCapacityOverrideMb": null
+    },
+    "text": "My post",
+    "cw": null,
+    "visibility": "public",
+    "renoteCount": 0,
+    "repliesCount": 0,
+    "reactions": {},
+    "reactionEmojis": [],
+    "emojis": [],
+    "tags": ["post"],
+    "fileIds": [],
+    "files": [],
+    "replyId": null,
+    "renoteId": null
+  }
+]
diff --git a/backend/test/support/data/json/misskey/peers.json b/backend/test/support/data/json/misskey/peers.json
new file mode 100644
index 0000000..af04900
--- /dev/null
+++ b/backend/test/support/data/json/misskey/peers.json
@@ -0,0 +1 @@
+["other.com"]
diff --git a/backend/test/support/data/json/misskey/stats.json b/backend/test/support/data/json/misskey/stats.json
new file mode 100644
index 0000000..9d80c51
--- /dev/null
+++ b/backend/test/support/data/json/misskey/stats.json
@@ -0,0 +1,10 @@
+{
+  "notesCount": 10,
+  "originalNotesCount": 20,
+  "usersCount": 10,
+  "originalUsersCount": 20,
+  "reactionsCount": 64569657,
+  "instances": 21184,
+  "driveUsageLocal": 0,
+  "driveUsageRemote": 0
+}
diff --git a/backend/test/test_helper.exs b/backend/test/test_helper.exs
index 292fc2d..287116a 100644
--- a/backend/test/test_helper.exs
+++ b/backend/test/test_helper.exs
@@ -3,3 +3,12 @@ Application.put_env(:backend, :http, HttpMock)
 
 ExUnit.start()
 Ecto.Adapters.SQL.Sandbox.mode(Backend.Repo, :manual)
+
+defmodule TestHelpers do
+  @spec load_json(String.t()) :: any()
+  def load_json(path) do
+    Path.join([__DIR__, "support", "data", "json", path])
+    |> File.read!()
+    |> Jason.decode!()
+  end
+end