diff --git a/Gemfile b/Gemfile
index 8b9174e..8ddb135 100644
--- a/Gemfile
+++ b/Gemfile
@@ -18,6 +18,9 @@ gem "turbo-rails"
 gem "stimulus-rails"
 # Build JSON APIs with ease [https://github.com/rails/jbuilder]
 gem "jbuilder"
+gem "grape"
+gem "grape-swagger"
+gem "rswag-ui"
 gem "caxlsx"
 gem "caxlsx_rails"
 
diff --git a/Gemfile.lock b/Gemfile.lock
index f218697..0f036ed 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -120,6 +120,26 @@ GEM
     docile (1.4.1)
     dotenv (3.2.0)
     drb (2.2.3)
+    dry-configurable (1.3.0)
+      dry-core (~> 1.1)
+      zeitwerk (~> 2.6)
+    dry-core (1.2.0)
+      concurrent-ruby (~> 1.0)
+      logger
+      zeitwerk (~> 2.6)
+    dry-inflector (1.3.1)
+    dry-logic (1.6.0)
+      bigdecimal
+      concurrent-ruby (~> 1.0)
+      dry-core (~> 1.1)
+      zeitwerk (~> 2.6)
+    dry-types (1.9.0)
+      bigdecimal (>= 3.0)
+      concurrent-ruby (~> 1.0)
+      dry-core (~> 1.0)
+      dry-inflector (~> 1.0)
+      dry-logic (~> 1.4)
+      zeitwerk (~> 2.6)
     ed25519 (1.4.0)
     erb (6.0.1)
     erubi (1.13.1)
@@ -131,6 +151,15 @@ GEM
       raabro (~> 1.4)
     globalid (1.3.0)
       activesupport (>= 6.1)
+    grape (3.1.1)
+      activesupport (>= 7.1)
+      dry-configurable
+      dry-types (>= 1.1)
+      mustermann-grape (~> 1.1.0)
+      rack (>= 2)
+      zeitwerk
+    grape-swagger (2.1.3)
+      grape (>= 1.7, < 4.0)
     htmlentities (4.4.2)
     i18n (1.14.8)
       concurrent-ruby (~> 1.0)
@@ -181,6 +210,10 @@ GEM
     minitest (6.0.1)
       prism (~> 1.5)
     msgpack (1.8.0)
+    mustermann (3.0.4)
+      ruby2_keywords (~> 0.0.1)
+    mustermann-grape (1.1.0)
+      mustermann (>= 1.0.0)
     net-imap (0.6.2)
       date
       net-protocol
@@ -273,6 +306,9 @@ GEM
       logger (~> 1)
       nokogiri (~> 1)
       rubyzip (>= 3.0.0, < 4.0.0)
+    rswag-ui (2.17.0)
+      actionpack (>= 5.2, < 8.2)
+      railties (>= 5.2, < 8.2)
     rubocop (1.84.0)
       json (~> 2.3)
       language_server-protocol (~> 3.17.0.2)
@@ -305,6 +341,7 @@ GEM
     ruby-vips (2.3.0)
       ffi (~> 1.12)
       logger
+    ruby2_keywords (0.0.5)
     rubyzip (3.2.2)
     securerandom (0.4.1)
     selenium-webdriver (4.40.0)
@@ -387,6 +424,8 @@ DEPENDENCIES
   caxlsx
   caxlsx_rails
   debug
+  grape
+  grape-swagger
   image_processing (~> 1.2)
   importmap-rails
   jbuilder
@@ -395,6 +434,7 @@ DEPENDENCIES
   puma (>= 5.0)
   rails (~> 8.1.2)
   roo (~> 3.0)
+  rswag-ui
   rubocop-rails-omakase
   selenium-webdriver
   simplecov
@@ -445,6 +485,11 @@ CHECKSUMS
   docile (1.4.1) sha256=96159be799bfa73cdb721b840e9802126e4e03dfc26863db73647204c727f21e
   dotenv (3.2.0) sha256=e375b83121ea7ca4ce20f214740076129ab8514cd81378161f11c03853fe619d
   drb (2.2.3) sha256=0b00d6fdb50995fe4a45dea13663493c841112e4068656854646f418fda13373
+  dry-configurable (1.3.0) sha256=882d862858567fc1210d2549d4c090f34370fc1bb7c5c1933de3fe792e18afa8
+  dry-core (1.2.0) sha256=0cc5a7da88df397f153947eeeae42e876e999c1e30900f3c536fb173854e96a1
+  dry-inflector (1.3.1) sha256=7fb0c2bb04f67638f25c52e7ba39ab435d922a3a5c3cd196120f63accb682dcc
+  dry-logic (1.6.0) sha256=da6fedbc0f90fc41f9b0cc7e6f05f5d529d1efaef6c8dcc8e0733f685745cea2
+  dry-types (1.9.0) sha256=7b656fe0a78d2432500ae1f29fefd6762f5a032ca7000e4f36bc111453d45d4d
   ed25519 (1.4.0) sha256=16e97f5198689a154247169f3453ef4cfd3f7a47481fde0ae33206cdfdcac506
   erb (6.0.1) sha256=28ecdd99c5472aebd5674d6061e3c6b0a45c049578b071e5a52c2a7f13c197e5
   erubi (1.13.1) sha256=a082103b0885dbc5ecf1172fede897f9ebdb745a4b97a5e8dc63953db1ee4ad9
@@ -452,6 +497,8 @@ CHECKSUMS
   ffi (1.17.3-x86_64-linux-gnu) sha256=3746b01f677aae7b16dc1acb7cb3cc17b3e35bdae7676a3f568153fb0e2c887f
   fugit (1.12.1) sha256=5898f478ede9b415f0804e42b8f3fd53f814bd85eebffceebdbc34e1107aaf68
   globalid (1.3.0) sha256=05c639ad6eb4594522a0b07983022f04aa7254626ab69445a0e493aa3786ff11
+  grape (3.1.1) sha256=774f16782d917a90e69de0499dfaab571e5ad967569ac066a2b0b918af12de69
+  grape-swagger (2.1.3) sha256=9ee955ada77c10ea2f2d2da5edcc4fc3cddcc40a6936f1b2558ee7b44e0f1153
   htmlentities (4.4.2) sha256=bbafbdf69f2eca9262be4efef7e43e6a1de54c95eb600f26984f71d2fe96c5c3
   i18n (1.14.8) sha256=285778639134865c5e0f6269e0b818256017e8cde89993fdfcbfb64d088824a5
   image_processing (1.14.0) sha256=754cc169c9c262980889bec6bfd325ed1dafad34f85242b5a07b60af004742fb
@@ -472,6 +519,8 @@ CHECKSUMS
   mini_mime (1.1.5) sha256=8681b7e2e4215f2a159f9400b5816d85e9d8c6c6b491e96a12797e798f8bccef
   minitest (6.0.1) sha256=7854c74f48e2e975969062833adc4013f249a4b212f5e7b9d5c040bf838d54bb
   msgpack (1.8.0) sha256=e64ce0212000d016809f5048b48eb3a65ffb169db22238fb4b72472fecb2d732
+  mustermann (3.0.4) sha256=85fadcb6b3c6493a8b511b42426f904b7f27b282835502233dd154daab13aa22
+  mustermann-grape (1.1.0) sha256=8d258a986004c8f01ce4c023c0b037c168a9ed889cf5778068ad54398fa458c5
   net-imap (0.6.2) sha256=08caacad486853c61676cca0c0c47df93db02abc4a8239a8b67eb0981428acc6
   net-pop (0.1.2) sha256=848b4e982013c15b2f0382792268763b748cce91c9e91e36b0f27ed26420dff3
   net-protocol (0.2.2) sha256=aa73e0cba6a125369de9837b8d8ef82a61849360eba0521900e2c3713aa162a8
@@ -508,6 +557,7 @@ CHECKSUMS
   reline (0.6.3) sha256=1198b04973565b36ec0f11542ab3f5cfeeec34823f4e54cebde90968092b1835
   rexml (3.4.4) sha256=19e0a2c3425dfbf2d4fc1189747bdb2f849b6c5e74180401b15734bc97b5d142
   roo (3.0.0) sha256=6fdd7a9158d657c69768b4168754ff2110cc21fdc01a1bec1010820cb05c91b1
+  rswag-ui (2.17.0) sha256=5f707b9b5e8171ddf9f519f6e401e79e419bd1d07387508603e76124f2443212
   rubocop (1.84.0) sha256=88dec310153bb685a879f5a7cdb601f6287b8f0ee675d9dc63a17c7204c4190a
   rubocop-ast (1.49.0) sha256=49c3676d3123a0923d333e20c6c2dbaaae2d2287b475273fddee0c61da9f71fd
   rubocop-performance (1.26.1) sha256=cd19b936ff196df85829d264b522fd4f98b6c89ad271fa52744a8c11b8f71834
@@ -515,6 +565,7 @@ CHECKSUMS
   rubocop-rails-omakase (1.1.0) sha256=2af73ac8ee5852de2919abbd2618af9c15c19b512c4cfc1f9a5d3b6ef009109d
   ruby-progressbar (1.13.0) sha256=80fc9c47a9b640d6834e0dc7b3c94c9df37f08cb072b7761e4a71e22cff29b33
   ruby-vips (2.3.0) sha256=e685ec02c13969912debbd98019e50492e12989282da5f37d05f5471442f5374
+  ruby2_keywords (0.0.5) sha256=ffd13740c573b7301cf7a2e61fc857b2a8e3d3aff32545d6f8300d8bae10e3ef
   rubyzip (3.2.2) sha256=c0ed99385f0625415c8f05bcae33fe649ed2952894a95ff8b08f26ca57ea5b3c
   securerandom (0.4.1) sha256=cc5193d414a4341b6e225f0cb4446aceca8e50d5e1888743fac16987638ea0b1
   selenium-webdriver (4.40.0) sha256=16ef7aa9853c1d4b9d52eac45aafa916e3934c5c83cb4facb03f250adfd15e5b
diff --git a/README.md b/README.md
index 094433f..bde9094 100644
--- a/README.md
+++ b/README.md
@@ -2,7 +2,7 @@
 
 ## Overview
 
-"Sanasto Wiki" is a web-based dictionary application for simultaneous translators in the living Christianity. The application provides publicly accessible translations while restricting editing and commenting to invited contributors.
+"Sanasto Wiki" is a web-based glossary for simultaneous translators in the living Christianity. The application provides publicly accessible translations while restricting editing and commenting to invited contributors.
 
 ---
 
@@ -188,15 +188,25 @@ See 'public/Kristillisyyden sanasto ver 23.5.2013.xlsx'
 
 ---
 
-## API (Optional Future)
+## API (Public Sync)
 
-REST API for potential mobile app or integration:
+Public JSON endpoint for syncing entries:
 ```
-GET    /api/entries
-GET    /api/entries/:id
-GET    /api/entries/search?q=:query&lang=:code
-POST   /api/entries (authenticated)
-PATCH  /api/entries/:id (authenticated)
+GET /api/entries
+GET /api/entries?since=2026-01-01T12:00:00Z
+```
+
+Responses include all language columns, category and `updated_at`. The optional `since`
+parameter filters by `updated_at` (ISO8601).
+
+Swagger docs:
+```
+GET /api/swagger
+```
+
+Swagger UI:
+```
+GET /api
 ```
 
 ## Deployment
diff --git a/app/controllers/api/base.rb b/app/controllers/api/base.rb
new file mode 100644
index 0000000..bfee9a6
--- /dev/null
+++ b/app/controllers/api/base.rb
@@ -0,0 +1,58 @@
+require "grape"
+require "grape-swagger"
+require "ostruct"
+
+class Api::Base < Grape::API
+  format :json
+  content_type :json, "application/json"
+
+  helpers do
+    def parse_since_param(raw_since)
+      return nil if raw_since.blank?
+
+      Time.iso8601(raw_since)
+    rescue ArgumentError
+      error!({ error: "Invalid since parameter. Use ISO8601 timestamp." }, 400)
+    end
+  end
+
+  resource :entries do
+    desc "Return public entries in all languages",
+         attributes: OpenStruct.new(success: nil, produces: nil)
+    params do
+      optional :since,
+               type: String,
+               desc: "ISO8601 timestamp. Returns entries updated after this time."
+    end
+    get do
+      since_time = parse_since_param(params[:since])
+
+      entries_scope = Entry.active_entries
+      entries_scope = entries_scope.where("updated_at > ?", since_time) if since_time
+
+      entries_scope
+        .order(:updated_at, :id)
+        .select(
+          :id,
+          :category,
+          :fi,
+          :en,
+          :sv,
+          :no,
+          :ru,
+          :de,
+          :updated_at
+        )
+    end
+  end
+
+  add_swagger_documentation(
+    info: {
+      title: "Sanasto Wiki API",
+      description: "Public sync API for Sanasto Wiki glossary entries."
+    },
+    mount_path: "/swagger",
+    hide_documentation_path: true,
+    format: :json
+  )
+end
diff --git a/config/initializers/rswag_ui.rb b/config/initializers/rswag_ui.rb
new file mode 100644
index 0000000..75937ec
--- /dev/null
+++ b/config/initializers/rswag_ui.rb
@@ -0,0 +1,3 @@
+Rswag::Ui.configure do |config|
+  config.swagger_endpoint "/api/swagger", "Sanasto Wiki API"
+end
diff --git a/config/routes.rb b/config/routes.rb
index e6ea5de..b6a2f85 100644
--- a/config/routes.rb
+++ b/config/routes.rb
@@ -51,6 +51,9 @@ Rails.application.routes.draw do
     end
   end
 
+  mount Api::Base => "/api"
+  mount Rswag::Ui::Engine => "/api"
+
   resources :entries do
     resources :comments, only: [ :create ]
     collection do
diff --git a/test/integration/api_entries_test.rb b/test/integration/api_entries_test.rb
new file mode 100644
index 0000000..406f388
--- /dev/null
+++ b/test/integration/api_entries_test.rb
@@ -0,0 +1,63 @@
+require "test_helper"
+
+class ApiEntriesTest < ActionDispatch::IntegrationTest
+  test "returns active entries with language fields" do
+    entry = entries(:one)
+
+    get "/api/entries"
+
+    assert_response :success
+    payload = JSON.parse(response.body)
+    entry_payload = payload.find { |item| item["id"] == entry.id }
+
+    assert_not_nil entry_payload
+    assert_equal entry.fi, entry_payload["fi"]
+    assert_equal entry.en, entry_payload["en"]
+    assert_equal entry.sv, entry_payload["sv"]
+    assert_equal entry.no, entry_payload["no"]
+    assert_equal entry.ru, entry_payload["ru"]
+    assert_equal entry.de, entry_payload["de"]
+  end
+
+  test "filters by updated_at when since param is provided" do
+    older_entry = Entry.create!(
+      fi: "Older Entry",
+      category: :word,
+      status: :active
+    )
+    older_entry.update_column(:updated_at, 2.days.ago)
+
+    newer_entry = Entry.create!(
+      fi: "Newer Entry",
+      category: :word,
+      status: :active
+    )
+    newer_entry.update_column(:updated_at, 1.hour.ago)
+
+    get "/api/entries", params: { since: 1.day.ago.iso8601 }
+
+    assert_response :success
+    payload = JSON.parse(response.body)
+    returned_ids = payload.map { |item| item["id"] }
+
+    assert_includes returned_ids, newer_entry.id
+    assert_not_includes returned_ids, older_entry.id
+  end
+
+  test "returns bad request for invalid since param" do
+    get "/api/entries", params: { since: "not-a-time" }
+
+    assert_response :bad_request
+    payload = JSON.parse(response.body)
+    assert_equal "Invalid since parameter. Use ISO8601 timestamp.", payload["error"]
+  end
+
+  test "exposes swagger docs" do
+    get "/api/swagger"
+
+    assert_response :success
+    payload = JSON.parse(response.body)
+    assert_equal "Sanasto Wiki API", payload.dig("info", "title")
+    assert_includes payload.keys, "paths"
+  end
+end