diff --git a/.github/workflows/test-authnz.yaml b/.github/workflows/test-authnz.yaml
index a2497807e45d..5e446ff1bad2 100644
--- a/.github/workflows/test-authnz.yaml
+++ b/.github/workflows/test-authnz.yaml
@@ -35,7 +35,7 @@ jobs:
         - chrome
         include:
         - erlang_version: "27.3"
-          elixir_version: 1.17.3
+          elixir_version: 1.18
     env:
       SELENIUM_DIR: selenium
       DOCKER_NETWORK: rabbitmq_net
diff --git a/.github/workflows/test-make-type-check.yaml b/.github/workflows/test-make-type-check.yaml
index 9862cd6aa050..5413e66e3d07 100644
--- a/.github/workflows/test-make-type-check.yaml
+++ b/.github/workflows/test-make-type-check.yaml
@@ -17,7 +17,7 @@ jobs:
         plugin:
           # These are using plugin-specific test jobs.
           - rabbit
-          # - rabbitmq_mqtt # disabled due to Elixir 1.18 JSON conficts
+          - rabbitmq_mqtt
           - rabbitmq_peer_discovery_aws
           # These are from the test-plugin test job.
           - amqp10_client
@@ -57,14 +57,14 @@ jobs:
           - rabbitmq_shovel
           - rabbitmq_shovel_management
           - rabbitmq_shovel_prometheus
-          # - rabbitmq_stomp # disabled due to Elixir 1.18 JSON conficts
-          # - rabbitmq_stream # disabled due to Elixir 1.18 JSON conficts
+          - rabbitmq_stomp
+          - rabbitmq_stream
           - rabbitmq_stream_common
           - rabbitmq_stream_management
           - rabbitmq_tracing
           - rabbitmq_trust_store
           - rabbitmq_web_dispatch
-          # - rabbitmq_web_mqtt # disabled due to Elixir 1.18 JSON conficts
+          - rabbitmq_web_mqtt
           - rabbitmq_web_stomp
           # This one we do not want to run tests so no corresponding test job.
           - rabbitmq_ct_helpers
diff --git a/.github/workflows/test-make.yaml b/.github/workflows/test-make.yaml
index c45d1ee2186b..49904aecff77 100644
--- a/.github/workflows/test-make.yaml
+++ b/.github/workflows/test-make.yaml
@@ -25,7 +25,7 @@ jobs:
         - '27'
         - '28'
         elixir_version:
-        - '1.18'
+        - '1.19'
     # @todo Add macOS and Windows.
     runs-on: ubuntu-latest
     timeout-minutes: 60
@@ -64,7 +64,7 @@ jobs:
         erlang_version:
         - '28'
         elixir_version:
-        - '1.18'
+        - '1.19'
     uses: ./.github/workflows/test-make-tests.yaml
     with:
       erlang_version: ${{ matrix.erlang_version }}
@@ -79,7 +79,7 @@ jobs:
         erlang_version:
         - '28'
         elixir_version:
-        - '1.18'
+        - '1.19'
     uses: ./.github/workflows/test-make-tests.yaml
     with:
       erlang_version: ${{ matrix.erlang_version }}
@@ -94,7 +94,7 @@ jobs:
         erlang_version: # Latest OTP
         - '28'
         elixir_version: # Latest Elixir
-        - '1.18'
+        - '1.19'
     uses: ./.github/workflows/test-make-type-check.yaml
     with:
       erlang_version: ${{ matrix.erlang_version }}
diff --git a/.github/workflows/test-management-ui-for-pr.yaml b/.github/workflows/test-management-ui-for-pr.yaml
index e233dbf63462..910a276eea6c 100644
--- a/.github/workflows/test-management-ui-for-pr.yaml
+++ b/.github/workflows/test-management-ui-for-pr.yaml
@@ -26,7 +26,7 @@ jobs:
         - chrome
         include:
         - erlang_version: "27.3"
-          elixir_version: 1.17
+          elixir_version: 1.18
     env:
       SELENIUM_DIR: selenium
       DOCKER_NETWORK: rabbitmq_net
diff --git a/.github/workflows/test-management-ui.yaml b/.github/workflows/test-management-ui.yaml
index f10a41becacb..adad108b72c0 100644
--- a/.github/workflows/test-management-ui.yaml
+++ b/.github/workflows/test-management-ui.yaml
@@ -33,7 +33,7 @@ jobs:
         - chrome
         include:
         - erlang_version: "27.3"
-          elixir_version: 1.17.3
+          elixir_version: 1.18
     env:
       SELENIUM_DIR: selenium
       DOCKER_NETWORK: rabbitmq_net
diff --git a/.github/workflows/test-upgrades.yaml b/.github/workflows/test-upgrades.yaml
index 52c2912d4284..df0b73d2ea8b 100644
--- a/.github/workflows/test-upgrades.yaml
+++ b/.github/workflows/test-upgrades.yaml
@@ -62,7 +62,7 @@ jobs:
         uses: erlef/setup-beam@v1
         with: # Versions repeated later in this file.
           otp-version: '27'
-          elixir-version: '1.18'
+          elixir-version: '1.19'
           hexpm-mirrors: |
             https://builds.hex.pm
             https://cdn.jsdelivr.net/hex
@@ -123,7 +123,7 @@ jobs:
         uses: erlef/setup-beam@v1
         with:
           otp-version: '27'
-          elixir-version: '1.18'
+          elixir-version: '1.19'
           hexpm-mirrors: |
             https://builds.hex.pm
             https://cdn.jsdelivr.net/hex
diff --git a/Makefile b/Makefile
index 88ae069746cb..e05ef6db346e 100644
--- a/Makefile
+++ b/Makefile
@@ -37,8 +37,6 @@ XREF_SCOPE = app deps
 # protocols directly.
 XREF_IGNORE = [ \
     {'Elixir.CSV.Encode',impl_for,1}, \
-    {'Elixir.JSON.Decoder',impl_for,1}, \
-    {'Elixir.JSON.Encoder',impl_for,1}, \
     {'Elixir.RabbitMQ.CLI.Core.DataCoercion',impl_for,1}]
 
 # Include Elixir libraries in the Xref checks.
diff --git a/deps/rabbitmq_cli/Makefile b/deps/rabbitmq_cli/Makefile
index 8c2b4f5dd434..90f96e5ec618 100644
--- a/deps/rabbitmq_cli/Makefile
+++ b/deps/rabbitmq_cli/Makefile
@@ -13,14 +13,13 @@ define PROJECT_ENV
 endef
 
 BUILD_DEPS = rabbit_common
-DEPS = csv json stdout_formatter
+DEPS = csv stdout_formatter
 LOCAL_DEPS = elixir
 
 TEST_DEPS = amqp amqp_client temp x509 rabbit
 
 dep_amqp = hex 3.3.0
 dep_csv = hex 3.2.1
-dep_json = hex 1.4.1
 dep_temp = hex 0.4.9
 dep_x509 = hex 0.9.2
 
@@ -141,6 +140,12 @@ endif
 dialyzer:: escript
 	MIX_ENV=test mix dialyzer
 
+# rabbitmq_cli is a pure Elixir project, so erlang.mk's `dialyze` target
+# has no .erl files to analyze. Override it as a successful no-op; use
+# `gmake dialyzer` (above) for an Elixir Dialyzer run via Mix.
+dialyze:
+	@:
+
 .PHONY: install
 
 install: $(ESCRIPT_FILE)
diff --git a/deps/rabbitmq_cli/lib/rabbitmq/cli/core/json.ex b/deps/rabbitmq_cli/lib/rabbitmq/cli/core/json.ex
new file mode 100644
index 000000000000..4401ce34aa41
--- /dev/null
+++ b/deps/rabbitmq_cli/lib/rabbitmq/cli/core/json.ex
@@ -0,0 +1,131 @@
+## This Source Code Form is subject to the terms of the Mozilla Public
+## License, v. 2.0. If a copy of the MPL was not distributed with this
+## file, You can obtain one at https://mozilla.org/MPL/2.0/.
+##
+## Copyright (c) 2007-2026 Broadcom. All Rights Reserved. The term “Broadcom” refers to Broadcom Inc. and/or its subsidiaries.  All rights reserved.
+
+defmodule RabbitMQ.CLI.Core.JSON do
+  @moduledoc """
+  Thin JSON facade used by the CLI tools.
+
+  Wraps `:thoas` so the rest of the codebase does not depend on a specific
+  backend, and so the module name does not collide with the `JSON` module
+  added to Elixir's standard library in 1.18.
+
+  `encode/1` returns `{:ok, binary}` and `decode/1` returns
+  `{:ok, term} | {:error, term}`, matching the shape that callers throughout
+  `rabbitmq_cli` already rely on.
+  """
+
+  @spec encode(term()) :: {:ok, binary()}
+  def encode(term) do
+    {:ok, :thoas.encode(normalize(term))}
+  end
+
+  @spec decode(iodata()) :: {:ok, term()} | {:error, term()}
+  def decode(bin) do
+    :thoas.decode(bin)
+  end
+
+  # Convert Erlang strings (lists of integers) to binaries for proper JSON
+  # encoding and convert other Erlang-specific terms to readable strings.
+  defp normalize(data) when is_function(data) do
+    "Fun()"
+  end
+
+  defp normalize(data) when is_pid(data) do
+    "Pid(#{inspect(data)})"
+  end
+
+  defp normalize(data) when is_port(data) do
+    "Port(#{inspect(data)})"
+  end
+
+  defp normalize(data) when is_reference(data) do
+    "Ref(#{inspect(data)})"
+  end
+
+  defp normalize(data) when is_binary(data) do
+    convert_binary(data)
+  end
+
+  defp normalize([]), do: []
+
+  # Likely a value like [5672], which we don't want to convert to the
+  # equivalent unicode codepoint.
+  defp normalize([val] = data) when is_integer(val) and val > 255 do
+    data
+  end
+
+  # Likely a value like [5672, 5682], which we don't want to convert to
+  # the equivalent unicode codepoint.
+  defp normalize([v0, v1] = data)
+       when is_integer(v0) and v0 > 255 and is_integer(v1) and v1 > 255 do
+    data
+  end
+
+  defp normalize([b | rest]) when is_binary(b) do
+    [convert_binary(b) | normalize(rest)]
+  end
+
+  defp normalize(data) when is_list(data) do
+    if proplist?(data) do
+      # `:thoas` encodes maps as JSON objects but is unreliable on lists of
+      # 2-tuples that contain non-proplist values nested inside, so we hand it
+      # a real map.
+      Map.new(data, fn {k, v} -> {normalize(k), normalize(v)} end)
+    else
+      try do
+        case :unicode.characters_to_binary(data, :utf8) do
+          binary when is_binary(binary) ->
+            binary
+
+          _ ->
+            Enum.map(data, &normalize/1)
+        end
+      rescue
+        ArgumentError ->
+          Enum.map(data, &normalize/1)
+      end
+    end
+  end
+
+  # `:thoas` does not accept bare tuples (only proplist 2-tuples nested in a
+  # list, handled above). Convert any other tuple to a list so it encodes as a
+  # JSON array, matching what the previous JSON library used to do.
+  defp normalize(data) when is_tuple(data) do
+    data
+    |> Tuple.to_list()
+    |> Enum.map(&normalize/1)
+  end
+
+  defp normalize(data) when is_map(data) do
+    Enum.into(data, %{}, fn {k, v} -> {normalize(k), normalize(v)} end)
+  end
+
+  defp normalize(data), do: data
+
+  defp proplist?([_ | _] = list) do
+    Enum.all?(list, fn
+      {k, _v} when is_atom(k) or is_binary(k) -> true
+      _ -> false
+    end)
+  end
+
+  defp proplist?(_), do: false
+
+  defp convert_binary(data) when is_binary(data) do
+    try do
+      case :unicode.characters_to_binary(data, :utf8) do
+        binary when is_binary(binary) ->
+          binary
+
+        _ ->
+          Base.encode64(data)
+      end
+    rescue
+      ArgumentError ->
+        Base.encode64(data)
+    end
+  end
+end
diff --git a/deps/rabbitmq_cli/lib/rabbitmq/cli/ctl/commands/export_definitions_command.ex b/deps/rabbitmq_cli/lib/rabbitmq/cli/ctl/commands/export_definitions_command.ex
index fbd1057eaa10..7d350ec21278 100644
--- a/deps/rabbitmq_cli/lib/rabbitmq/cli/ctl/commands/export_definitions_command.ex
+++ b/deps/rabbitmq_cli/lib/rabbitmq/cli/ctl/commands/export_definitions_command.ex
@@ -151,7 +151,7 @@ defmodule RabbitMQ.CLI.Ctl.Commands.ExportDefinitionsCommand do
   defp serialise(raw_map, "json") do
     # rabbit_definitions already takes care of transforming all
     # proplists into maps
-    {:ok, json} = JSON.encode(raw_map)
+    {:ok, json} = RabbitMQ.CLI.Core.JSON.encode(raw_map)
     json
   end
 
diff --git a/deps/rabbitmq_cli/lib/rabbitmq/cli/ctl/commands/import_definitions_command.ex b/deps/rabbitmq_cli/lib/rabbitmq/cli/ctl/commands/import_definitions_command.ex
index 442727a930d0..dd7dd33db179 100644
--- a/deps/rabbitmq_cli/lib/rabbitmq/cli/ctl/commands/import_definitions_command.ex
+++ b/deps/rabbitmq_cli/lib/rabbitmq/cli/ctl/commands/import_definitions_command.ex
@@ -166,7 +166,7 @@ defmodule RabbitMQ.CLI.Ctl.Commands.ImportDefinitionsCommand do
   #
 
   defp deserialise(bin, "json") do
-    JSON.decode(bin)
+    RabbitMQ.CLI.Core.JSON.decode(bin)
   end
 
   defp deserialise(bin, "erlang") do
diff --git a/deps/rabbitmq_cli/lib/rabbitmq/cli/ctl/commands/list_user_limits_command.ex b/deps/rabbitmq_cli/lib/rabbitmq/cli/ctl/commands/list_user_limits_command.ex
index bbad0501c9fe..3c91a08c4c63 100644
--- a/deps/rabbitmq_cli/lib/rabbitmq/cli/ctl/commands/list_user_limits_command.ex
+++ b/deps/rabbitmq_cli/lib/rabbitmq/cli/ctl/commands/list_user_limits_command.ex
@@ -36,7 +36,7 @@ defmodule RabbitMQ.CLI.Ctl.Commands.ListUserLimitsCommand do
 
       val ->
         Enum.map(val, fn {user, val} ->
-          {:ok, val_encoded} = JSON.encode(Map.new(val))
+          {:ok, val_encoded} = RabbitMQ.CLI.Core.JSON.encode(Map.new(val))
           [user: user, limits: val_encoded]
         end)
     end
@@ -56,7 +56,7 @@ defmodule RabbitMQ.CLI.Ctl.Commands.ListUserLimitsCommand do
         {:badrpc, node}
 
       val when is_list(val) or is_map(val) ->
-        {:ok, val_encoded} = JSON.encode(Map.new(val))
+        {:ok, val_encoded} = RabbitMQ.CLI.Core.JSON.encode(Map.new(val))
         val_encoded
     end
   end
diff --git a/deps/rabbitmq_cli/lib/rabbitmq/cli/ctl/commands/list_vhost_limits_command.ex b/deps/rabbitmq_cli/lib/rabbitmq/cli/ctl/commands/list_vhost_limits_command.ex
index 1d8fb36aef6a..a91108046b50 100644
--- a/deps/rabbitmq_cli/lib/rabbitmq/cli/ctl/commands/list_vhost_limits_command.ex
+++ b/deps/rabbitmq_cli/lib/rabbitmq/cli/ctl/commands/list_vhost_limits_command.ex
@@ -36,7 +36,7 @@ defmodule RabbitMQ.CLI.Ctl.Commands.ListVhostLimitsCommand do
 
       val ->
         Enum.map(val, fn {vhost, val} ->
-          {:ok, val_encoded} = JSON.encode(Map.new(val))
+          {:ok, val_encoded} = RabbitMQ.CLI.Core.JSON.encode(Map.new(val))
           [vhost: vhost, limits: val_encoded]
         end)
     end
@@ -54,7 +54,7 @@ defmodule RabbitMQ.CLI.Ctl.Commands.ListVhostLimitsCommand do
         {:badrpc, node}
 
       val when is_list(val) or is_map(val) ->
-        JSON.encode(Map.new(val))
+        RabbitMQ.CLI.Core.JSON.encode(Map.new(val))
     end
   end
 
diff --git a/deps/rabbitmq_cli/lib/rabbitmq/cli/formatters/json.ex b/deps/rabbitmq_cli/lib/rabbitmq/cli/formatters/json.ex
index 382ebfe251f8..b8844009380f 100644
--- a/deps/rabbitmq_cli/lib/rabbitmq/cli/formatters/json.ex
+++ b/deps/rabbitmq_cli/lib/rabbitmq/cli/formatters/json.ex
@@ -18,7 +18,7 @@ defmodule RabbitMQ.CLI.Formatters.Json do
   end
 
   def format_output(output, _opts) do
-    {:ok, json} = JSON.encode(keys_to_atoms(convert_erlang_strings(output)))
+    {:ok, json} = RabbitMQ.CLI.Core.JSON.encode(keys_to_atoms(output))
     json
   end
 
@@ -72,94 +72,4 @@ defmodule RabbitMQ.CLI.Formatters.Json do
   end
 
   def machine_readable?, do: true
-
-  # Convert Erlang strings (lists of integers) to binaries for proper JSON encoding
-  # Also convert other Erlang-specific terms to readable strings
-  defp convert_erlang_strings(data) when is_function(data) do
-    "Fun()"
-  end
-
-  defp convert_erlang_strings(data) when is_pid(data) do
-    "Pid(#{inspect(data)})"
-  end
-
-  defp convert_erlang_strings(data) when is_port(data) do
-    "Port(#{inspect(data)})"
-  end
-
-  defp convert_erlang_strings(data) when is_reference(data) do
-    "Ref(#{inspect(data)})"
-  end
-
-  defp convert_erlang_strings(data) when is_binary(data) do
-    convert_binary(data)
-  end
-
-  defp convert_erlang_strings([]),  do: []
-
-  defp convert_erlang_strings([val]=data) when is_integer(val) and val > 255 do
-    # This is likely a value like [5672], which we don't want
-    # to convert to the equivalent unicode codepoint.
-    data
-  end
-
-  defp convert_erlang_strings([v0, v1]=data) when
-    is_integer(v0) and v0 > 255 and is_integer(v1) and v1 > 255 do
-    # This is likely a value like [5672, 5682], which we don't want
-    # to convert to the equivalent unicode codepoint.
-    data
-  end
-
-  defp convert_erlang_strings([b | rest]) when is_binary(b) do
-      [convert_binary(b) | convert_erlang_strings(rest)]
-  end
-
-  defp convert_erlang_strings(data) when is_list(data) do
-    try do
-      case :unicode.characters_to_binary(data, :utf8) do
-        binary when is_binary(binary) ->
-          # Successfully converted - it was a valid Unicode string
-          binary
-        _ ->
-          # Conversion failed - not a Unicode string, process as regular list
-          Enum.map(data, &convert_erlang_strings/1)
-      end
-    rescue
-      ArgumentError ->
-        # badarg exception - not valid character data, process as regular list
-        Enum.map(data, &convert_erlang_strings/1)
-    end
-  end
-
-  defp convert_erlang_strings(data) when is_tuple(data) do
-    data
-    |> Tuple.to_list()
-    |> Enum.map(&convert_erlang_strings/1)
-    |> List.to_tuple()
-  end
-
-  defp convert_erlang_strings(data) when is_map(data) do
-    Enum.into(data, %{}, fn {k, v} ->
-      {convert_erlang_strings(k), convert_erlang_strings(v)}
-    end)
-  end
-
-  defp convert_erlang_strings(data), do: data
-
-  defp convert_binary(data) when is_binary(data) do
-    try do
-      case :unicode.characters_to_binary(data, :utf8) do
-        binary when is_binary(binary) ->
-          # Successfully converted - it was a valid Unicode string
-          binary
-        _ ->
-          # Conversion failed - not a Unicode string
-          Base.encode64(data)
-      end
-    rescue
-      ArgumentError ->
-        # badarg exception - just base64 encode it.
-        Base.encode64(data)
-    end
-  end
 end
diff --git a/deps/rabbitmq_cli/lib/rabbitmq/cli/formatters/json_stream.ex b/deps/rabbitmq_cli/lib/rabbitmq/cli/formatters/json_stream.ex
index fc08edf2a042..2ef210bcc66e 100644
--- a/deps/rabbitmq_cli/lib/rabbitmq/cli/formatters/json_stream.ex
+++ b/deps/rabbitmq_cli/lib/rabbitmq/cli/formatters/json_stream.ex
@@ -31,7 +31,7 @@ defmodule RabbitMQ.CLI.Formatters.JsonStream do
   end
 
   def format_output(output, _opts) do
-    {:ok, json} = JSON.encode(keys_to_atoms(output))
+    {:ok, json} = RabbitMQ.CLI.Core.JSON.encode(keys_to_atoms(output))
     json
   end
 
diff --git a/deps/rabbitmq_cli/lib/rabbitmqctl.ex b/deps/rabbitmq_cli/lib/rabbitmqctl.ex
index 561b978d12bb..019925acd2d1 100644
--- a/deps/rabbitmq_cli/lib/rabbitmqctl.ex
+++ b/deps/rabbitmq_cli/lib/rabbitmqctl.ex
@@ -569,7 +569,7 @@ defmodule RabbitMQCtl do
   end
 
   defp format_error({:error, :check_failed, err}, %{formatter: "json"}, _) when is_map(err) do
-    {:ok, res} = JSON.encode(err)
+    {:ok, res} = RabbitMQ.CLI.Core.JSON.encode(err)
     {:error, ExitCodes.exit_unavailable(), res}
   end
 
@@ -589,12 +589,12 @@ defmodule RabbitMQCtl do
 
   # Catch all clauses
   defp format_error({:error, err}, %{formatter: "json"}, _) when is_map(err) do
-    {:ok, res} = JSON.encode(err)
+    {:ok, res} = RabbitMQ.CLI.Core.JSON.encode(err)
     {:error, ExitCodes.exit_unavailable(), res}
   end
 
   defp format_error({:error, exit_code, err}, %{formatter: "json"}, _) when is_map(err) do
-    {:ok, res} = JSON.encode(err)
+    {:ok, res} = RabbitMQ.CLI.Core.JSON.encode(err)
     {:error, exit_code, res}
   end
 
diff --git a/deps/rabbitmq_cli/mix.exs b/deps/rabbitmq_cli/mix.exs
index d91a78ba6aa8..e61874adda42 100644
--- a/deps/rabbitmq_cli/mix.exs
+++ b/deps/rabbitmq_cli/mix.exs
@@ -11,7 +11,7 @@ defmodule RabbitMQCtl.MixfileBase do
     [
       app: :rabbitmqctl,
       version: "4.0.0-dev",
-      elixir: ">= 1.13.4 and < 1.20.0",
+      elixir: ">= 1.17.0 and < 1.20.0",
       build_embedded: Mix.env() == :prod,
       start_permanent: Mix.env() == :prod,
       escript: [
@@ -26,8 +26,8 @@ defmodule RabbitMQCtl.MixfileBase do
         exclude: [
           CSV,
           CSV.Encode,
-          JSON,
           :mnesia,
+          :thoas,
           :msacc,
           :public_key,
           :pubkey_cert,
@@ -141,8 +141,9 @@ defmodule RabbitMQCtl.MixfileBase do
     # Note that normal deps will be fetched by Erlang.mk on build.
     [
       {
-        :json,
-        path: Path.join(deps_dir, "json")
+        :thoas,
+        path: Path.join(deps_dir, "thoas"),
+        override: true
       },
       {
         :csv,
diff --git a/deps/rabbitmq_cli/test/core/json_test.exs b/deps/rabbitmq_cli/test/core/json_test.exs
new file mode 100644
index 000000000000..d26cfc843873
--- /dev/null
+++ b/deps/rabbitmq_cli/test/core/json_test.exs
@@ -0,0 +1,127 @@
+## This Source Code Form is subject to the terms of the Mozilla Public
+## License, v. 2.0. If a copy of the MPL was not distributed with this
+## file, You can obtain one at https://mozilla.org/MPL/2.0/.
+##
+## Copyright (c) 2007-2026 Broadcom. All Rights Reserved. The term “Broadcom” refers to Broadcom Inc. and/or its subsidiaries.  All rights reserved.
+
+defmodule RabbitMQ.CLI.Core.JSONTest do
+  use ExUnit.Case, async: true
+
+  alias RabbitMQ.CLI.Core.JSON
+
+  describe "encode/1 + decode/1 round-trip" do
+    test "encodes and decodes a flat map with atom keys" do
+      {:ok, bin} = JSON.encode(%{a: 1, b: "two"})
+      assert {:ok, %{"a" => 1, "b" => "two"}} == JSON.decode(bin)
+    end
+
+    test "encodes and decodes nested maps" do
+      {:ok, bin} = JSON.encode(%{outer: %{inner: [<<"a">>, <<"b">>]}})
+      assert {:ok, %{"outer" => %{"inner" => ["a", "b"]}}} == JSON.decode(bin)
+    end
+
+    test "decodes returns {:error, _} on invalid JSON" do
+      assert {:error, _} = JSON.decode("not json")
+    end
+  end
+
+  describe "encode/1 — proplist to JSON object" do
+    test "atom-keyed proplist becomes a JSON object" do
+      {:ok, bin} = JSON.encode(a: 1, b: 2)
+      assert {:ok, %{"a" => 1, "b" => 2}} == JSON.decode(bin)
+    end
+
+    test "binary-keyed proplist becomes a JSON object" do
+      {:ok, bin} = JSON.encode([{<<"a">>, 1}, {<<"b">>, 2}])
+      assert {:ok, %{"a" => 1, "b" => 2}} == JSON.decode(bin)
+    end
+
+    test "empty list stays an empty JSON array, not an object" do
+      {:ok, bin} = JSON.encode([])
+      assert {:ok, []} == JSON.decode(bin)
+    end
+
+    test "list of mixed elements is encoded as a JSON array, not an object" do
+      {:ok, bin} = JSON.encode([{:a, 1}, "loose"])
+      assert {:ok, [["a", 1], "loose"]} == JSON.decode(bin)
+    end
+  end
+
+  describe "encode/1 — bare tuple handling (regression for cluster_nodes-style values)" do
+    test "a non-proplist 2-tuple value is encoded as a JSON array" do
+      # `:cluster_nodes` in rabbit's environment looks like
+      # `{[node1, node2], :disc}`. Before the fix, this crashed `:thoas` with
+      # `function_clause` because the first element of the tuple is a list,
+      # not an atom or binary, so it does not match thoas's proplist heuristic.
+      input = [cluster_nodes: {[:rabbit@n1, :rabbit@n2], :disc}]
+      {:ok, bin} = JSON.encode(input)
+      assert {:ok, %{"cluster_nodes" => [["rabbit@n1", "rabbit@n2"], "disc"]}} ==
+               JSON.decode(bin)
+    end
+
+    test "a 3-tuple value is encoded as a 3-element JSON array" do
+      {:ok, bin} = JSON.encode(point: {1, 2, 3})
+      assert {:ok, %{"point" => [1, 2, 3]}} == JSON.decode(bin)
+    end
+
+    test "a deeply nested non-proplist tuple is encoded as a JSON array" do
+      {:ok, bin} = JSON.encode(outer: %{inner: {1, 2}})
+      assert {:ok, %{"outer" => %{"inner" => [1, 2]}}} == JSON.decode(bin)
+    end
+  end
+
+  describe "encode/1 — Erlang string and port number heuristics" do
+    test "an Erlang charlist is encoded as a JSON string" do
+      {:ok, bin} = JSON.encode(host: ~c"localhost")
+      assert {:ok, %{"host" => "localhost"}} == JSON.decode(bin)
+    end
+
+    test "a single integer port stays a one-element JSON array" do
+      {:ok, bin} = JSON.encode(tcp_listeners: [5672])
+      assert {:ok, %{"tcp_listeners" => [5672]}} == JSON.decode(bin)
+    end
+
+    test "two integer ports stay a two-element JSON array" do
+      {:ok, bin} = JSON.encode(tcp_listeners: [5672, 5683])
+      assert {:ok, %{"tcp_listeners" => [5672, 5683]}} == JSON.decode(bin)
+    end
+
+    test "a list of binaries is preserved" do
+      {:ok, bin} = JSON.encode(files: [<<"a.conf">>, <<"b.conf">>])
+      assert {:ok, %{"files" => ["a.conf", "b.conf"]}} == JSON.decode(bin)
+    end
+
+    # Documented footgun: an integer list whose values are valid Unicode
+    # codepoints is treated as an Erlang charlist and coerced to a binary.
+    # The `[5672]` and `[5672, 5683]` special cases above exist precisely to
+    # avoid this for typical port-number values.
+    test "an integer list with small values is coerced to a string (charlist)" do
+      {:ok, bin} = JSON.encode(%{xs: [1, 2, 3]})
+      assert {:ok, %{"xs" => <<1, 2, 3>>}} == JSON.decode(bin)
+    end
+  end
+
+  describe "encode/1 — Erlang-specific terms become readable strings" do
+    test "a pid is encoded as a Pid(...) string" do
+      {:ok, bin} = JSON.encode(%{p: self()})
+      assert {:ok, %{"p" => "Pid(" <> _}} = JSON.decode(bin)
+    end
+
+    test "a reference is encoded as a Ref(...) string" do
+      {:ok, bin} = JSON.encode(%{r: make_ref()})
+      assert {:ok, %{"r" => "Ref(" <> _}} = JSON.decode(bin)
+    end
+
+    test "a function is encoded as Fun()" do
+      {:ok, bin} = JSON.encode(%{f: fn -> :ok end})
+      assert {:ok, %{"f" => "Fun()"}} == JSON.decode(bin)
+    end
+
+    test "a binary with invalid UTF-8 falls back to Base64" do
+      invalid = <<0xFF, 0xFE>>
+      {:ok, bin} = JSON.encode(%{b: invalid})
+      assert {:ok, %{"b" => encoded}} = JSON.decode(bin)
+      assert encoded == Base.encode64(invalid)
+    end
+  end
+end
diff --git a/deps/rabbitmq_cli/test/ctl/export_definitions_command_test.exs b/deps/rabbitmq_cli/test/ctl/export_definitions_command_test.exs
index a5aaaefb37df..82c31ef3e2da 100644
--- a/deps/rabbitmq_cli/test/ctl/export_definitions_command_test.exs
+++ b/deps/rabbitmq_cli/test/ctl/export_definitions_command_test.exs
@@ -111,7 +111,7 @@ defmodule ExportDefinitionsCommandTest do
     {:ok, nil} = @command.run([valid_file_path()], context[:opts])
 
     {:ok, bin} = File.read(valid_file_path())
-    {:ok, map} = JSON.decode(bin)
+    {:ok, map} = RabbitMQ.CLI.Core.JSON.decode(bin)
     assert Map.has_key?(map, "rabbitmq_version")
   end
 
@@ -128,7 +128,7 @@ defmodule ExportDefinitionsCommandTest do
     clear_parameter("/", "federation-upstream", "up-1")
 
     {:ok, bin} = File.read(valid_file_path())
-    {:ok, map} = JSON.decode(bin)
+    {:ok, map} = RabbitMQ.CLI.Core.JSON.decode(bin)
     assert Map.has_key?(map, "rabbitmq_version")
     params = map["parameters"]
     assert is_map(hd(params)["value"])
diff --git a/deps/rabbitmq_cli/test/ctl/set_user_limits_command_test.exs b/deps/rabbitmq_cli/test/ctl/set_user_limits_command_test.exs
index 9fc9e51f6763..4db343db7501 100644
--- a/deps/rabbitmq_cli/test/ctl/set_user_limits_command_test.exs
+++ b/deps/rabbitmq_cli/test/ctl/set_user_limits_command_test.exs
@@ -131,6 +131,6 @@ defmodule SetUserLimitsCommandTest do
 
   defp assert_limits(context, definition) do
     limits = get_user_limits(context[:user])
-    assert {:ok, limits} == JSON.decode(definition)
+    assert {:ok, limits} == RabbitMQ.CLI.Core.JSON.decode(definition)
   end
 end
diff --git a/deps/rabbitmq_cli/test/ctl/set_vhost_limits_command_test.exs b/deps/rabbitmq_cli/test/ctl/set_vhost_limits_command_test.exs
index 118223887802..817ce90e645c 100644
--- a/deps/rabbitmq_cli/test/ctl/set_vhost_limits_command_test.exs
+++ b/deps/rabbitmq_cli/test/ctl/set_vhost_limits_command_test.exs
@@ -138,6 +138,6 @@ defmodule SetVhostLimitsCommandTest do
 
   defp assert_limits(context) do
     limits = get_vhost_limits(context[:vhost])
-    assert {:ok, limits} == JSON.decode(context[:definition])
+    assert {:ok, limits} == RabbitMQ.CLI.Core.JSON.decode(context[:definition])
   end
 end
diff --git a/deps/rabbitmq_cli/test/json_formatting_test.exs b/deps/rabbitmq_cli/test/json_formatting_test.exs
index 45545390beb0..23bb2d204d67 100644
--- a/deps/rabbitmq_cli/test/json_formatting_test.exs
+++ b/deps/rabbitmq_cli/test/json_formatting_test.exs
@@ -29,7 +29,7 @@ defmodule JSONFormattingTest do
         error_check(command, exit_ok())
       end)
 
-    {:ok, doc} = JSON.decode(output)
+    {:ok, doc} = RabbitMQ.CLI.Core.JSON.decode(output)
 
     assert Map.has_key?(doc, "memory")
     assert Map.has_key?(doc, "listeners")
@@ -67,7 +67,7 @@ defmodule JSONFormattingTest do
         error_check(command, exit_ok())
       end)
 
-    {:ok, doc} = JSON.decode(output)
+    {:ok, doc} = RabbitMQ.CLI.Core.JSON.decode(output)
 
     assert Map.has_key?(doc, "running_nodes")
     running_nodes = doc["running_nodes"]
@@ -93,7 +93,7 @@ defmodule JSONFormattingTest do
         error_check(command, exit_ok())
       end)
 
-    {:ok, doc} = JSON.decode(output)
+    {:ok, doc} = RabbitMQ.CLI.Core.JSON.decode(output)
     assert Map.has_key?(doc, "rabbit")
     rabbit = doc["rabbit"]
     assert Map.has_key?(rabbit, "data_dir")
diff --git a/deps/rabbitmq_cli/test/test_helper.exs b/deps/rabbitmq_cli/test/test_helper.exs
index 260ef8a67d6a..40cbf759f52d 100644
--- a/deps/rabbitmq_cli/test/test_helper.exs
+++ b/deps/rabbitmq_cli/test/test_helper.exs
@@ -19,7 +19,6 @@ true = Code.append_path(Path.join([System.get_env("DEPS_DIR"), "rabbit_common",
 true = Code.append_path(Path.join([System.get_env("DEPS_DIR"), "rabbit", "ebin"]))
 
 true = Code.append_path(Path.join(["_build", Atom.to_string(Mix.env()), "lib", "amqp", "ebin"]))
-true = Code.append_path(Path.join(["_build", Atom.to_string(Mix.env()), "lib", "json", "ebin"]))
 true = Code.append_path(Path.join(["_build", Atom.to_string(Mix.env()), "lib", "x509", "ebin"]))
 
 if function_exported?(Mix, :ensure_application!, 1) do
diff --git a/deps/rabbitmq_mqtt/src/rabbit_mqtt_processor.erl b/deps/rabbitmq_mqtt/src/rabbit_mqtt_processor.erl
index a21b83da44d7..bc96bf00a7df 100644
--- a/deps/rabbitmq_mqtt/src/rabbit_mqtt_processor.erl
+++ b/deps/rabbitmq_mqtt/src/rabbit_mqtt_processor.erl
@@ -89,11 +89,6 @@
          %% Maximum MQTT packet size in bytes for packets sent from server to client.
          max_packet_size_outbound :: max_packet_size(),
          topic_alias_maximum_outbound :: non_neg_integer(),
-         %% https://github.com/rabbitmq/rabbitmq-server/issues/13040
-         %% The database stores the MQTT subscription options in the binding arguments for:
-         %% * v1 as Erlang record #mqtt_subscription_opts{}
-         %% * v2 as AMQP 0.9.1 table
-         binding_args_v2 :: boolean(),
          msg_interceptor_ctx :: rabbit_msg_interceptor:context()
         }).