diff --git a/CHANGELOG.md b/CHANGELOG.md
index adc6747..55a6dc7 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -5,7 +5,22 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
-## UNRELEASED
+## 0.17.0 - 2026-01-22
+
+### Breaking Changes
+
+-   **Minimum OTP version is now 27** - LiveSvelte now uses Erlang's native `:json` module by default
+-   **Minimum Elixir version is now 1.17** - Required for OTP 27 support
+-   **Jason is now optional** - Add `{:jason, "~> 1.2"}` to your deps if you want to use Jason instead of native JSON
+
+### Changed
+
+-   Default JSON library changed from Jason to native Erlang `:json` module (`LiveSvelte.JSON`)
+-   Structs are automatically converted to maps by the native JSON encoder (no `@derive` needed)
+
+### Added
+
+-   New `LiveSvelte.JSON` module that wraps Erlang's native `:json` module with a Jason-compatible interface
 
 ## 0.16.0 - 2025-04-18
 
diff --git a/README.md b/README.md
index 76b17df..90a21ef 100644
--- a/README.md
+++ b/README.md
@@ -92,7 +92,7 @@ _If you're updating from an older version, make sure to check the `CHANGELOG.md`
 ```elixir
 defp deps do
   [
-    {:live_svelte, "~> 0.16.0"}
+    {:live_svelte, "~> 0.17.0"}
   ]
 end
 ```
@@ -487,6 +487,43 @@ To disable SSR on a specific component, set the `ssr` property to false. Like so
 <.svelte name="Example" ssr={false} />
 ```
 
+### JSON Library
+
+LiveSvelte uses Erlang/OTP 27's native `:json` module by default for JSON encoding.
+This provides excellent performance without requiring external dependencies.
+
+**Note:** LiveSvelte requires Elixir 1.17+ and OTP 27+ for the native JSON module.
+
+#### Using Jason or Poison
+
+If you prefer to use Jason, Poison, or another JSON library, configure it in your `config.exs`:
+
+```elixir
+# config/config.exs
+config :live_svelte, json_library: Jason
+```
+
+Add the dependency to your `mix.exs`:
+
+```elixir
+# mix.exs
+defp deps do
+  [
+    {:live_svelte, "~> 0.17"},
+    {:jason, "~> 1.2"}  # or {:poison, "~> 5.0"}
+  ]
+end
+```
+
+The JSON library must implement `encode!/1` that accepts any Elixir term and returns a JSON string.
+
+#### Struct Encoding
+
+The native JSON encoder automatically converts structs to maps before encoding. This means
+you don't need `@derive Jason.Encoder` when using the default native JSON encoder.
+
+If you're using Jason and need custom struct encoding behavior, see the
+[Structs and Ecto](#structs-and-ecto) section for details on `@derive Jason.Encoder`.
 
 ### live_json
 
@@ -527,12 +564,15 @@ You can find an example [here](https://github.com/woutdp/live_svelte/blob/master
 
 ### Structs and Ecto
 
-We use [Jason](https://github.com/michalmuskala/jason) to serialize any data you pass in the props so it can be handled by Javascript.
-Jason doesn't know how to handle structs by default, so you need to define it yourself.
+LiveSvelte serializes data passed in props to JSON so it can be handled by JavaScript.
 
-#### Structs
+**With native JSON (default):** Structs are automatically converted to maps. No additional configuration needed.
 
-For example, if you have a regular struct like this:
+**With Jason:** Jason doesn't know how to handle structs by default, so you need to define it yourself using `@derive`.
+
+#### Structs (Jason only)
+
+If you're using Jason and have a struct like this:
 
 ```elixir
 defmodule User do
@@ -558,9 +598,9 @@ defmodule User do
 end
 ```
 
-#### Ecto
+#### Ecto (Jason only)
 
-In ecto's case it's important to _also_ omit the `__meta__` field as it's not serializable.
+When using Jason with Ecto schemas, it's important to _also_ omit the `__meta__` field as it's not serializable.
 
 Check out the following example:
 
diff --git a/assets/package-lock.json b/assets/package-lock.json
index 569705a..abffe6a 100644
--- a/assets/package-lock.json
+++ b/assets/package-lock.json
@@ -31,7 +31,6 @@
             "integrity": "sha512-30iZtAPgz+LTIYoeivqYo853f02jBYSd5uGnGpkFV0M3xOt9aN73erkgYAmZU43x4VfqcnLxW9Kpg3R5LC4YYw==",
             "dev": true,
             "license": "Apache-2.0",
-            "peer": true,
             "dependencies": {
                 "@jridgewell/gen-mapping": "^0.3.5",
                 "@jridgewell/trace-mapping": "^0.3.24"
@@ -454,7 +453,6 @@
             "integrity": "sha512-IzL8ZoEDIBRWEzlCcRhOaCupYyN5gdIK+Q6fbFdPDg6HqX6jpkItn7DFIpW9LQzXG6Df9sA7+OKnq0qlz/GaQg==",
             "dev": true,
             "license": "MIT",
-            "peer": true,
             "dependencies": {
                 "@jridgewell/set-array": "^1.2.1",
                 "@jridgewell/sourcemap-codec": "^1.4.10",
@@ -480,7 +478,6 @@
             "integrity": "sha512-R8gLRTZeyp03ymzP/6Lil/28tGeGEzhx1q2k703KGWRAI1VdvPIXdG70VJc2pAMw3NA6JKL5hhFu1sJX0Mnn/A==",
             "dev": true,
             "license": "MIT",
-            "peer": true,
             "engines": {
                 "node": ">=6.0.0"
             }
@@ -508,8 +505,7 @@
             "resolved": "https://registry.npmjs.org/@types/estree/-/estree-1.0.6.tgz",
             "integrity": "sha512-AYnb1nQyY49te+VRAVgmzfcgjYS91mY5P0TKUDCLEM+gNnA+3T6rWITXRLYCpahpqSQbN5cE+gHpnPyXjHWxcw==",
             "dev": true,
-            "license": "MIT",
-            "peer": true
+            "license": "MIT"
         },
         "node_modules/acorn": {
             "version": "8.14.0",
@@ -531,7 +527,6 @@
             "integrity": "sha512-xsc9Xv0xlVfwp2o7sQ+GCQ1PgbkdcpWdTzrwXxO3xDMTAywVS3oXVOcOHuRjAPkS4P9b+yc/qNF15460v+jp4Q==",
             "dev": true,
             "license": "MIT",
-            "peer": true,
             "peerDependencies": {
                 "acorn": ">=8.9.0"
             }
@@ -542,7 +537,6 @@
             "integrity": "sha512-COROpnaoap1E2F000S62r6A60uHZnmlvomhfyT2DlTcrY1OrBKn2UhH7qn5wTC9zMvD0AY7csdPSNwKP+7WiQw==",
             "dev": true,
             "license": "Apache-2.0",
-            "peer": true,
             "engines": {
                 "node": ">= 0.4"
             }
@@ -553,7 +547,6 @@
             "integrity": "sha512-qIj0G9wZbMGNLjLmg1PT6v2mE9AH2zlnADJD/2tC6E00hgmhUOfEB6greHPAfLRSufHqROIUTkw6E+M3lH0PTQ==",
             "dev": true,
             "license": "Apache-2.0",
-            "peer": true,
             "engines": {
                 "node": ">= 0.4"
             }
@@ -565,6 +558,7 @@
             "dev": true,
             "hasInstallScript": true,
             "license": "MIT",
+            "peer": true,
             "bin": {
                 "esbuild": "bin/esbuild"
             },
@@ -620,8 +614,7 @@
             "resolved": "https://registry.npmjs.org/esm-env/-/esm-env-1.1.4.tgz",
             "integrity": "sha512-oO82nKPHKkzIj/hbtuDYy/JHqBHFlMIW36SDiPCVsj87ntDLcWN+sJ1erdVryd4NxODacFTsdrIE3b7IamqbOg==",
             "dev": true,
-            "license": "MIT",
-            "peer": true
+            "license": "MIT"
         },
         "node_modules/esrap": {
             "version": "1.2.2",
@@ -629,7 +622,6 @@
             "integrity": "sha512-F2pSJklxx1BlQIQgooczXCPHmcWpn6EsP5oo73LQfonG9fIlIENQ8vMmfGXeojP9MrkzUNAfyU5vdFlR9shHAw==",
             "dev": true,
             "license": "MIT",
-            "peer": true,
             "dependencies": {
                 "@jridgewell/sourcemap-codec": "^1.4.15",
                 "@types/estree": "^1.0.1"
@@ -641,7 +633,6 @@
             "integrity": "sha512-v3rht/LgVcsdZa3O2Nqs+NMowLOxeOm7Ay9+/ARQ2F+qEoANRcqrjAZKGN0v8ymUetZGgkp26LTnGT7H0Qo9Pg==",
             "dev": true,
             "license": "MIT",
-            "peer": true,
             "dependencies": {
                 "@types/estree": "*"
             }
@@ -651,8 +642,7 @@
             "resolved": "https://registry.npmjs.org/locate-character/-/locate-character-3.0.0.tgz",
             "integrity": "sha512-SW13ws7BjaeJ6p7Q6CO2nchbYEc3X3J6WrmTTDto7yMPqVSZTUyY5Tjbid+Ab8gLnATtygYtiDIJGQRRn2ZOiA==",
             "dev": true,
-            "license": "MIT",
-            "peer": true
+            "license": "MIT"
         },
         "node_modules/magic-string": {
             "version": "0.30.12",
@@ -660,7 +650,6 @@
             "integrity": "sha512-Ea8I3sQMVXr8JhN4z+H/d8zwo+tYDgHE9+5G4Wnrwhs0gaK9fXTKx0Tw5Xwsd/bCPTTZNRAdpyzvoeORe9LYpw==",
             "dev": true,
             "license": "MIT",
-            "peer": true,
             "dependencies": {
                 "@jridgewell/sourcemap-codec": "^1.5.0"
             }
@@ -708,8 +697,7 @@
             "resolved": "https://registry.npmjs.org/zimmerframe/-/zimmerframe-1.1.2.tgz",
             "integrity": "sha512-rAbqEGa8ovJy4pyBxZM70hg4pE6gDgaQ0Sl9M3enG3I0d6H4XSAM3GeNGLKnsBpuijUow064sf7ww1nutC5/3w==",
             "dev": true,
-            "license": "MIT",
-            "peer": true
+            "license": "MIT"
         }
     }
 }
diff --git a/config/config.exs b/config/config.exs
index 80a2033..7a1435a 100644
--- a/config/config.exs
+++ b/config/config.exs
@@ -3,6 +3,7 @@ import Config
 config :live_svelte,
   ssr_module: LiveSvelte.SSR.NodeJS,
   ssr: true
+  # json_library defaults to LiveSvelte.JSON (native Erlang :json module)
 
 # if Mix.env() == :dev do
 #   esbuild = fn args ->
diff --git a/lib/live_svelte.ex b/lib/live_svelte.ex
index 9618cd5..3729d4e 100644
--- a/lib/live_svelte.ex
+++ b/lib/live_svelte.ex
@@ -94,19 +94,20 @@ defmodule LiveSvelte do
       <script>
         <%= raw(@ssr_render["head"]) %>
       </script>
-      <div
-        id={id(@name)}
-        data-name={@name}
-        data-props={json(@props)}
-        data-ssr={@ssr_render != nil}
-        data-live-json={
-          if @init, do: json(@live_json_props), else: @live_json_props |> Map.keys() |> json()
-        }
-        data-slots={@slots |> Slots.base_encode_64() |> json}
-        phx-update="ignore"
-        phx-hook="SvelteHook"
-        class={@class}
-      >
+    <% svelte_id = id(@name) %>
+    <div
+      id={svelte_id}
+      data-name={@name}
+      data-props={json(@props)}
+      data-ssr={@ssr_render != nil}
+      data-live-json={
+        if @init, do: json(@live_json_props), else: @live_json_props |> Map.keys() |> json()
+      }
+      data-slots={@slots |> Slots.base_encode_64() |> json}
+      phx-hook="SvelteHook"
+      class={@class}
+    >
+      <div id={"#{svelte_id}-target"} data-svelte-target phx-update="ignore">
         <%= raw(@ssr_render["head"]) %>
         <style>
           <%= raw(@ssr_render["css"]["code"]) %>
@@ -114,6 +115,7 @@ defmodule LiveSvelte do
         <%= raw(@ssr_render["html"]) %>
         <%= render_slot(@loading) %>
       </div>
+    </div>
     </.live_json>
     """
   end
@@ -128,7 +130,8 @@ defmodule LiveSvelte do
   end
 
   defp json(props) do
-    Jason.encode!(props)
+    json_library = Application.get_env(:live_svelte, :json_library, LiveSvelte.JSON)
+    json_library.encode!(props)
   end
 
   defp id(name), do: "#{name}-#{System.unique_integer([:positive])}"
diff --git a/lib/live_svelte/json.ex b/lib/live_svelte/json.ex
new file mode 100644
index 0000000..e84ceb3
--- /dev/null
+++ b/lib/live_svelte/json.ex
@@ -0,0 +1,102 @@
+defmodule LiveSvelte.JSON do
+  @moduledoc """
+  JSON encoding using Erlang/OTP 27's native :json module.
+
+  This module provides a Jason-compatible interface (`encode!/1`)
+  that wraps the native Erlang :json module for use with LiveSvelte.
+
+  ## Features
+
+  - Uses Erlang's built-in `:json` module (OTP 27+)
+  - Automatically converts structs to maps
+  - Converts all map keys to strings (matching Jason behavior)
+  - Handles nested data structures
+
+  ## Usage
+
+  This module is the default JSON encoder for LiveSvelte. To use a different
+  encoder like Jason, configure it in your `config.exs`:
+
+      config :live_svelte, json_library: Jason
+
+  ## SSR Compatibility Note
+
+  When using server-side rendering, the NodeJS worker uses Jason internally
+  to serialize data to the Node.js process. This module is designed to produce
+  Jason-compatible output, ensuring consistency between SSR and client-side
+  hydration.
+
+  """
+
+  @doc """
+  Encodes an Elixir term to a JSON string.
+
+  Structs are automatically converted to maps before encoding.
+  Returns a binary string.
+
+  ## Examples
+
+      iex> LiveSvelte.JSON.encode!(%{foo: "bar"})
+      "{\"foo\":\"bar\"}"
+
+      iex> LiveSvelte.JSON.encode!([1, 2, 3])
+      "[1,2,3]"
+
+  """
+  @spec encode!(term()) :: binary()
+  def encode!(term) do
+    term
+    |> prepare_term()
+    |> :json.encode()
+    |> IO.iodata_to_binary()
+  end
+
+  # Recursively prepare terms for JSON encoding.
+  # Converts structs to maps, nil to null, and handles nested structures.
+
+  # nil becomes JSON null
+  defp prepare_term(nil), do: :null
+
+  # Booleans pass through (Erlang :json handles them)
+  defp prepare_term(true), do: true
+  defp prepare_term(false), do: false
+
+  # Other atoms become strings (matches Jason behavior)
+  defp prepare_term(atom) when is_atom(atom) do
+    Atom.to_string(atom)
+  end
+
+  # Structs become maps (strip __struct__ key)
+  defp prepare_term(%_{} = struct) do
+    struct
+    |> Map.from_struct()
+    |> prepare_term()
+  end
+
+  # Maps: convert all keys to strings, recursively process values
+  defp prepare_term(map) when is_map(map) do
+    Map.new(map, fn {k, v} -> {prepare_key(k), prepare_term(v)} end)
+  end
+
+  # Lists: recursively process elements
+  defp prepare_term(list) when is_list(list) do
+    Enum.map(list, &prepare_term/1)
+  end
+
+  # Tuples become arrays
+  defp prepare_term(tuple) when is_tuple(tuple) do
+    tuple
+    |> Tuple.to_list()
+    |> prepare_term()
+  end
+
+  # Numbers and binaries pass through
+  defp prepare_term(term), do: term
+
+  # Key conversion helpers - ensure all keys become strings
+  defp prepare_key(key) when is_atom(key), do: Atom.to_string(key)
+  defp prepare_key(key) when is_integer(key), do: Integer.to_string(key)
+  defp prepare_key(key) when is_float(key), do: Float.to_string(key)
+  defp prepare_key(key) when is_binary(key), do: key
+  defp prepare_key(key), do: to_string(key)
+end
diff --git a/mix.exs b/mix.exs
index b68ec26..2890c7c 100644
--- a/mix.exs
+++ b/mix.exs
@@ -1,14 +1,15 @@
 defmodule LiveSvelte.MixProject do
   use Mix.Project
 
-  @version "0.16.0"
+  @version "0.17.0"
   @repo_url "https://github.com/woutdp/live_svelte"
 
   def project do
     [
       app: :live_svelte,
       version: @version,
-      elixir: "~> 1.12",
+      elixir: "~> 1.17",
+      elixirc_paths: elixirc_paths(Mix.env()),
       start_permanent: Mix.env() == :prod,
       aliases: aliases(),
       deps: deps(),
@@ -53,10 +54,13 @@ defmodule LiveSvelte.MixProject do
     ]
   end
 
+  defp elixirc_paths(:test), do: ["lib", "test/support"]
+  defp elixirc_paths(_), do: ["lib"]
+
   defp deps do
     [
       {:ex_doc, "~> 0.37.3", only: :dev, runtime: false},
-      {:jason, "~> 1.2"},
+      {:jason, "~> 1.2", optional: true},
       {:nodejs, "~> 3.1"},
       {:phoenix, ">= 1.7.0"},
       {:phoenix_html, ">= 3.3.1"},
diff --git a/package.json b/package.json
index 592b895..e1325ab 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
     "name": "live_svelte",
-    "version": "0.16.0",
+    "version": "0.17.0",
     "description": "",
     "license": "MIT",
     "module": "./priv/static/live_svelte.esm.js",
diff --git a/test/json_library_test.exs b/test/json_library_test.exs
new file mode 100644
index 0000000..26dd4c2
--- /dev/null
+++ b/test/json_library_test.exs
@@ -0,0 +1,152 @@
+defmodule LiveSvelte.JSONLibraryTest do
+  # must be synchronous, tests are sensitive to config changes
+  use ExUnit.Case, async: false
+
+  describe "native JSON library (default)" do
+    test "uses LiveSvelte.JSON by default when no config is provided" do
+      Application.delete_env(:live_svelte, :json_library)
+      json_library = Application.get_env(:live_svelte, :json_library, LiveSvelte.JSON)
+      assert json_library == LiveSvelte.JSON
+    end
+
+    test "encodes props correctly with native JSON" do
+      Application.delete_env(:live_svelte, :json_library)
+
+      data = %{foo: "bar", baz: 123}
+
+      # Call the private json/1 function through the public API
+      # by testing that the component renders with correct data attributes
+      assigns = %{
+        __changed__: nil,
+        socket: nil,
+        name: "Test",
+        props: data,
+        live_json_props: %{},
+        ssr: false,
+        class: nil,
+        loading: [],
+        inner_block: []
+      }
+
+      result = LiveSvelte.svelte(assigns)
+      html = Phoenix.HTML.Safe.to_iodata(result) |> IO.iodata_to_binary()
+
+      # HTML entities are escaped in the output
+      # Native JSON encodes correctly
+      assert html =~ "data-props="
+      assert html =~ "foo"
+      assert html =~ "bar"
+      assert html =~ "baz"
+      assert html =~ "123"
+    end
+  end
+
+  describe "custom JSON library" do
+    test "uses custom library when configured" do
+      load_config("test/json_library_test/custom_json_config.exs")
+      json_library = Application.get_env(:live_svelte, :json_library)
+      assert json_library == TestJSONLibrary
+    end
+
+    test "calls custom library's encode!/1 function" do
+      load_config("test/json_library_test/custom_json_config.exs")
+
+      data = %{test: "data"}
+
+      assigns = %{
+        __changed__: nil,
+        socket: nil,
+        name: "Test",
+        props: data,
+        live_json_props: %{},
+        ssr: false,
+        class: nil,
+        loading: [],
+        inner_block: []
+      }
+
+      result = LiveSvelte.svelte(assigns)
+      html = Phoenix.HTML.Safe.to_iodata(result) |> IO.iodata_to_binary()
+
+      # Should contain the test library's output
+      assert html =~ ~s(data-props="TEST_ENCODED:%{test: &quot;data&quot;}")
+    end
+  end
+
+  describe "backward compatibility with Jason" do
+    test "works with Jason when explicitly configured" do
+      Application.put_env(:live_svelte, :json_library, Jason)
+
+      json_library = Application.get_env(:live_svelte, :json_library)
+      assert json_library == Jason
+
+      data = %{legacy: "test"}
+
+      assigns = %{
+        __changed__: nil,
+        socket: nil,
+        name: "Legacy",
+        props: data,
+        live_json_props: %{},
+        ssr: false,
+        class: nil,
+        loading: [],
+        inner_block: []
+      }
+
+      result = LiveSvelte.svelte(assigns)
+      html = Phoenix.HTML.Safe.to_iodata(result) |> IO.iodata_to_binary()
+
+      # HTML entities are escaped in the output
+      assert html =~ ~s(data-props="{&quot;legacy&quot;:&quot;test&quot;}")
+
+      # Clean up
+      Application.delete_env(:live_svelte, :json_library)
+    end
+  end
+
+  describe "struct encoding" do
+    defmodule TestUser do
+      defstruct name: "John", age: 27
+    end
+
+    test "native JSON encodes structs as maps automatically" do
+      Application.delete_env(:live_svelte, :json_library)
+
+      data = %{user: %TestUser{name: "Jane", age: 30}}
+
+      assigns = %{
+        __changed__: nil,
+        socket: nil,
+        name: "StructTest",
+        props: data,
+        live_json_props: %{},
+        ssr: false,
+        class: nil,
+        loading: [],
+        inner_block: []
+      }
+
+      result = LiveSvelte.svelte(assigns)
+      html = Phoenix.HTML.Safe.to_iodata(result) |> IO.iodata_to_binary()
+
+      # Should encode struct fields
+      assert html =~ "user"
+      assert html =~ "name"
+      assert html =~ "Jane"
+      assert html =~ "age"
+      assert html =~ "30"
+    end
+  end
+
+  # Helper function to reload configuration
+  # Pattern copied from ssr_test.exs:27-34
+  defp load_config(path) do
+    Application.started_applications(:infinity)
+    |> Enum.reduce([], fn {app, _, _}, acc ->
+      [{app, Application.get_all_env(app)} | acc]
+    end)
+    |> Config.Reader.merge(Config.Reader.read!(path))
+    |> Application.put_all_env()
+  end
+end
diff --git a/test/json_library_test/custom_json_config.exs b/test/json_library_test/custom_json_config.exs
new file mode 100644
index 0000000..d0c2d77
--- /dev/null
+++ b/test/json_library_test/custom_json_config.exs
@@ -0,0 +1,3 @@
+import Config
+
+config :live_svelte, json_library: TestJSONLibrary
diff --git a/test/live_svelte/json_test.exs b/test/live_svelte/json_test.exs
new file mode 100644
index 0000000..f5b492d
--- /dev/null
+++ b/test/live_svelte/json_test.exs
@@ -0,0 +1,208 @@
+defmodule LiveSvelte.JSONTest do
+  use ExUnit.Case, async: true
+
+  alias LiveSvelte.JSON
+
+  describe "encode!/1" do
+    test "encodes simple maps" do
+      assert JSON.encode!(%{foo: "bar"}) == ~s({"foo":"bar"})
+    end
+
+    test "encodes nested maps" do
+      result = JSON.encode!(%{outer: %{inner: "value"}})
+      assert result == ~s({"outer":{"inner":"value"}})
+    end
+
+    test "encodes lists" do
+      assert JSON.encode!([1, 2, 3]) == "[1,2,3]"
+    end
+
+    test "encodes lists of maps" do
+      result = JSON.encode!([%{a: 1}, %{b: 2}])
+      assert result == ~s([{"a":1},{"b":2}])
+    end
+
+    test "encodes integers" do
+      assert JSON.encode!(42) == "42"
+    end
+
+    test "encodes floats" do
+      assert JSON.encode!(3.14) == "3.14"
+    end
+
+    test "encodes booleans" do
+      assert JSON.encode!(true) == "true"
+      assert JSON.encode!(false) == "false"
+    end
+
+    test "encodes nil as null" do
+      assert JSON.encode!(nil) == "null"
+    end
+
+    test "encodes strings" do
+      assert JSON.encode!("hello") == ~s("hello")
+    end
+
+    test "encodes atoms as strings" do
+      assert JSON.encode!(:hello) == ~s("hello")
+    end
+
+    test "encodes maps with atom keys" do
+      result = JSON.encode!(%{foo: "bar", baz: 123})
+      # Map key order may vary, so we parse and compare
+      assert result =~ "foo"
+      assert result =~ "bar"
+      assert result =~ "baz"
+      assert result =~ "123"
+    end
+
+    test "encodes maps with string keys" do
+      assert JSON.encode!(%{"foo" => "bar"}) == ~s({"foo":"bar"})
+    end
+  end
+
+  describe "struct encoding" do
+    defmodule TestStruct do
+      defstruct name: "test", value: 42
+    end
+
+    defmodule NestedStruct do
+      defstruct user: nil, data: %{}
+    end
+
+    test "encodes structs as maps" do
+      result = JSON.encode!(%TestStruct{})
+      decoded = :json.decode(result)
+      assert decoded["name"] == "test"
+      assert decoded["value"] == 42
+    end
+
+    test "encodes structs with custom values" do
+      result = JSON.encode!(%TestStruct{name: "custom", value: 100})
+      decoded = :json.decode(result)
+      assert decoded["name"] == "custom"
+      assert decoded["value"] == 100
+    end
+
+    test "encodes nested structs" do
+      nested = %NestedStruct{
+        user: %TestStruct{name: "john", value: 30},
+        data: %{key: "value"}
+      }
+
+      result = JSON.encode!(nested)
+      decoded = :json.decode(result)
+      assert decoded["user"]["name"] == "john"
+      assert decoded["user"]["value"] == 30
+      assert decoded["data"]["key"] == "value"
+    end
+
+    test "encodes structs in lists" do
+      list = [%TestStruct{name: "a"}, %TestStruct{name: "b"}]
+      result = JSON.encode!(list)
+      decoded = :json.decode(result)
+      assert length(decoded) == 2
+      assert Enum.at(decoded, 0)["name"] == "a"
+      assert Enum.at(decoded, 1)["name"] == "b"
+    end
+  end
+
+  describe "tuple encoding" do
+    test "encodes tuples as arrays" do
+      assert JSON.encode!({1, 2, 3}) == "[1,2,3]"
+    end
+
+    test "encodes tuples with mixed types" do
+      result = JSON.encode!({"hello", 42, true})
+      assert result == ~s(["hello",42,true])
+    end
+  end
+
+  describe "edge cases" do
+    test "encodes empty map" do
+      assert JSON.encode!(%{}) == "{}"
+    end
+
+    test "encodes empty list" do
+      assert JSON.encode!([]) == "[]"
+    end
+
+    test "encodes deeply nested structures" do
+      deep = %{a: %{b: %{c: %{d: [1, 2, %{e: "f"}]}}}}
+      result = JSON.encode!(deep)
+      decoded = :json.decode(result)
+      assert get_in(decoded, ["a", "b", "c", "d"]) |> Enum.at(2) |> Map.get("e") == "f"
+    end
+  end
+
+  describe "integer key handling" do
+    test "encodes maps with integer keys as string keys" do
+      result = JSON.encode!(%{1 => "a", 2 => "b"})
+      decoded = :json.decode(result)
+      assert Map.has_key?(decoded, "1")
+      assert Map.has_key?(decoded, "2")
+      assert decoded["1"] == "a"
+      assert decoded["2"] == "b"
+    end
+
+    test "encodes large maps with integer keys (LiveJson scenario)" do
+      data = for i <- 1..100, into: %{}, do: {i, i * 2}
+      result = JSON.encode!(data)
+      decoded = :json.decode(result)
+      assert decoded["1"] == 2
+      assert decoded["50"] == 100
+      assert decoded["100"] == 200
+    end
+
+    test "encodes nested maps with integer keys" do
+      data = %{1 => %{2 => "nested"}}
+      result = JSON.encode!(data)
+      decoded = :json.decode(result)
+      assert decoded["1"]["2"] == "nested"
+    end
+
+    test "encodes mixed key types" do
+      data = %{1 => "int", :atom => "atom", "string" => "string"}
+      result = JSON.encode!(data)
+      decoded = :json.decode(result)
+      assert decoded["1"] == "int"
+      assert decoded["atom"] == "atom"
+      assert decoded["string"] == "string"
+    end
+  end
+
+  describe "atom value handling" do
+    test "encodes atom values as strings" do
+      result = JSON.encode!(%{status: :active})
+      decoded = :json.decode(result)
+      assert decoded["status"] == "active"
+    end
+
+    test "preserves boolean atoms" do
+      assert JSON.encode!(true) == "true"
+      assert JSON.encode!(false) == "false"
+    end
+
+    test "encodes atom values in lists" do
+      result = JSON.encode!([:one, :two, :three])
+      assert result == ~s(["one","two","three"])
+    end
+
+    test "encodes mixed atom and string values" do
+      result = JSON.encode!(%{atom_val: :test, string_val: "test"})
+      decoded = :json.decode(result)
+      assert decoded["atom_val"] == "test"
+      assert decoded["string_val"] == "test"
+    end
+  end
+
+  describe "float key handling" do
+    test "encodes maps with float keys as string keys" do
+      result = JSON.encode!(%{1.5 => "float"})
+      decoded = :json.decode(result)
+      # Float.to_string may produce different representations
+      assert map_size(decoded) == 1
+      assert Enum.at(Map.values(decoded), 0) == "float"
+    end
+  end
+end
diff --git a/test/support/test_json_library.ex b/test/support/test_json_library.ex
new file mode 100644
index 0000000..fefbf64
--- /dev/null
+++ b/test/support/test_json_library.ex
@@ -0,0 +1,8 @@
+defmodule TestJSONLibrary do
+  @moduledoc false
+  # Mock JSON library for testing custom configuration
+
+  def encode!(data) do
+    "TEST_ENCODED:#{inspect(data)}"
+  end
+end