diff --git a/lib/req_llm/application.ex b/lib/req_llm/application.ex
index 71d75526..3ea64fa6 100644
--- a/lib/req_llm/application.ex
+++ b/lib/req_llm/application.ex
@@ -20,10 +20,15 @@ defmodule ReqLLM.Application do
 
   @impl true
   def start(_type, _args) do
-    if Application.get_env(:req_llm, :load_dotenv, true) do
+    req_llm_load_dotenv = Application.get_env(:req_llm, :load_dotenv, true)
+
+    sync_llm_db_dotenv_config(req_llm_load_dotenv)
+
+    if req_llm_load_dotenv do
       load_dotenv()
     end
 
+    ensure_llm_db_started()
     initialize_registry()
     initialize_schema_cache()
 
@@ -127,6 +132,23 @@ defmodule ReqLLM.Application do
     ])
   end
 
+  defp sync_llm_db_dotenv_config(req_llm_load_dotenv) do
+    case Application.fetch_env(:llm_db, :load_dotenv) do
+      :error ->
+        Application.put_env(:llm_db, :load_dotenv, req_llm_load_dotenv)
+
+      {:ok, _value} ->
+        :ok
+    end
+  end
+
+  defp ensure_llm_db_started do
+    case Application.ensure_all_started(:llm_db) do
+      {:ok, _} -> :ok
+      {:error, reason} -> raise "failed to start :llm_db: #{inspect(reason)}"
+    end
+  end
+
   defp load_dotenv do
     env_file = Path.join(File.cwd!(), ".env")
 
diff --git a/mix.exs b/mix.exs
index 07e75009..84fd26b2 100644
--- a/mix.exs
+++ b/mix.exs
@@ -19,7 +19,7 @@ defmodule ReqLLM.MixProject do
 
       # Dialyzer configuration
       dialyzer: [
-        plt_add_apps: [:mix],
+        plt_add_apps: [:mix, :llm_db],
         exclude_paths: ["test/support"]
       ],
 
@@ -185,6 +185,7 @@ defmodule ReqLLM.MixProject do
   def application do
     [
       extra_applications: [:logger, :xmerl],
+      included_applications: [:llm_db],
       mod: {ReqLLM.Application, []}
     ]
   end
diff --git a/test/req_llm/application_test.exs b/test/req_llm/application_test.exs
index be9b922e..e3001c33 100644
--- a/test/req_llm/application_test.exs
+++ b/test/req_llm/application_test.exs
@@ -1,6 +1,26 @@
 defmodule ReqLLM.ApplicationTest do
   use ExUnit.Case, async: false
 
+  @dotenv_key "REQ_LLM_ISSUE_527_DOTENV_KEY"
+
+  setup do
+    original_req_llm_load_dotenv = Application.get_env(:req_llm, :load_dotenv)
+    original_llm_db_load_dotenv = Application.get_env(:llm_db, :load_dotenv)
+
+    on_exit(fn ->
+      stop_app(:req_llm)
+      stop_app(:llm_db)
+      restore_app_env(:req_llm, :load_dotenv, original_req_llm_load_dotenv)
+      restore_app_env(:llm_db, :load_dotenv, original_llm_db_load_dotenv)
+      System.delete_env(@dotenv_key)
+      Application.ensure_all_started(:llm_db)
+      LLMDB.load(custom: Application.get_env(:llm_db, :custom, %{}))
+      Application.ensure_all_started(:req_llm)
+    end)
+
+    :ok
+  end
+
   describe "load_dotenv configuration" do
     test "get_finch_config/0 returns default configuration" do
       config = ReqLLM.Application.get_finch_config()
@@ -40,5 +60,73 @@ defmodule ReqLLM.ApplicationTest do
         end
       end
     end
+
+    test "load_dotenv false prevents llm_db from loading .env during req_llm startup" do
+      with_apps_stopped(fn ->
+        with_temp_dir(fn ->
+          File.write!(".env", "#{@dotenv_key}=from_file\n")
+          System.delete_env(@dotenv_key)
+          Application.put_env(:req_llm, :load_dotenv, false)
+          Application.delete_env(:llm_db, :load_dotenv)
+
+          assert {:ok, _} = Application.ensure_all_started(:req_llm)
+          assert System.get_env(@dotenv_key) == nil
+        end)
+      end)
+    end
+
+    test "startup does not overwrite existing env vars from .env files" do
+      with_apps_stopped(fn ->
+        with_temp_dir(fn ->
+          File.write!(".env", "#{@dotenv_key}=from_file\n")
+          System.put_env(@dotenv_key, "from_env")
+          Application.delete_env(:req_llm, :load_dotenv)
+          Application.delete_env(:llm_db, :load_dotenv)
+
+          assert {:ok, _} = Application.ensure_all_started(:req_llm)
+          assert System.get_env(@dotenv_key) == "from_env"
+        end)
+      end)
+    end
+
+    test "explicit llm_db load_dotenv config overrides req_llm default" do
+      with_apps_stopped(fn ->
+        with_temp_dir(fn ->
+          File.write!(".env", "#{@dotenv_key}=from_file\n")
+          System.delete_env(@dotenv_key)
+          Application.put_env(:req_llm, :load_dotenv, false)
+          Application.put_env(:llm_db, :load_dotenv, true)
+
+          assert {:ok, _} = Application.ensure_all_started(:req_llm)
+          assert System.get_env(@dotenv_key) == "from_file"
+        end)
+      end)
+    end
+  end
+
+  defp with_apps_stopped(fun) do
+    stop_app(:req_llm)
+    stop_app(:llm_db)
+    fun.()
+  end
+
+  defp with_temp_dir(fun) do
+    path = Path.join(System.tmp_dir!(), "req-llm-issue-527-#{System.unique_integer([:positive])}")
+    File.mkdir_p!(path)
+
+    try do
+      File.cd!(path, fun)
+    after
+      File.rm_rf!(path)
+    end
+  end
+
+  defp stop_app(app) do
+    if Keyword.has_key?(Application.started_applications(), app) do
+      Application.stop(app)
+    end
   end
+
+  defp restore_app_env(app, key, nil), do: Application.delete_env(app, key)
+  defp restore_app_env(app, key, value), do: Application.put_env(app, key, value)
 end