diff --git a/lib/tests/modules.sh b/lib/tests/modules.sh
index 8ea8adab72c9d..b3ce45514502c 100755
--- a/lib/tests/modules.sh
+++ b/lib/tests/modules.sh
@@ -58,12 +58,19 @@ logFailure() {
 evalConfig() {
     local attr=$1
     shift
-    local script="import ./default.nix { modules = [ $* ];}"
+
+    local nix_args=()
+
     if [ "${ABORT_ON_WARN-0}" = "1" ]; then
-      local-nix-instantiate --option abort-on-warn true -E "$script" -A "$attr"
-    else
-      local-nix-instantiate -E "$script" -A "$attr"
+        nix_args+=(--option abort-on-warn true)
     fi
+
+    if [ "${STRICT_EVAL-0}" = "1" ]; then
+        nix_args+=(--strict)
+    fi
+
+    local script="import ./default.nix { modules = [ $* ];}"
+    local-nix-instantiate "${nix_args[@]}" -E "$script" -A "$attr"
 }
 
 reportFailure() {
@@ -247,6 +254,19 @@ checkConfigError 'A definition for option .* is not of type .fileset.. Definitio
 checkConfigError 'A definition for option .* is not of type .fileset.. Definition values:\n.*' config.filesetCardinal.err3 ./fileset.nix
 checkConfigError 'A definition for option .* is not of type .fileset.. Definition values:\n.*' config.filesetCardinal.err4 ./fileset.nix
 
+# types.mkStructuredType
+checkConfigOutput '^null$' config.nullableValue.null ./types.nix
+checkConfigOutput '^true$' config.nullableValue.bool ./types.nix
+checkConfigOutput '^1$' config.nullableValue.int ./types.nix
+checkConfigOutput '^1.1$' config.nullableValue.float ./types.nix
+checkConfigOutput '^"foo"$' config.nullableValue.str ./types.nix
+checkConfigOutput '^".*/store.*"$' config.nullableValue.path ./types.nix
+STRICT_EVAL=1 checkConfigOutput '^\{"foo":1\}$' config.nullableValue.attrs ./types.nix
+STRICT_EVAL=1 checkConfigOutput '^\[\{"bar":\[1\]\}\]$' config.nullableValue.list ./types.nix
+
+checkConfigError 'A definition for option .* is not of type .VAL value.. .*' config.nullableValue.lambda ./types.nix
+checkConfigError 'A definition for option .* is not of type .VAL value.. .*' config.structuredValue.null ./types.nix
+
 # Check boolean option.
 checkConfigOutput '^false$' config.enable ./declare-enable.nix
 checkConfigError 'The option .* does not exist. Definition values:\n\s*- In .*: true' config.enable ./define-enable.nix
diff --git a/lib/tests/modules/types.nix b/lib/tests/modules/types.nix
index 0a566ea960c43..78216342fe16b 100644
--- a/lib/tests/modules/types.nix
+++ b/lib/tests/modules/types.nix
@@ -16,6 +16,17 @@ in
   options = {
     pathInStore = mkOption { type = types.lazyAttrsOf types.pathInStore; };
     externalPath = mkOption { type = types.lazyAttrsOf types.externalPath; };
+    # mkStructuredType
+    nullableValue = mkOption { type = types.attrsOf (types.mkStructuredType { typeName = "VAL"; }); };
+    structuredValue = mkOption {
+      type = types.attrsOf (
+        types.mkStructuredType {
+          typeName = "VAL";
+          nullable = false;
+        }
+      );
+    };
+
     assertions = mkOption { };
   };
   config = {
@@ -35,6 +46,22 @@ in
     externalPath.ok1 = "/foo/bar";
     externalPath.ok2 = "/";
 
+    # mkStructuredType { nullable = true; }
+    nullableValue.null = null; # null
+    nullableValue.bool = true; # bool
+    nullableValue.int = 1; # int
+    nullableValue.float = 1.1; # float
+    nullableValue.str = "foo"; # str
+    nullableValue.path = ./.; # path
+    nullableValue.attrs = {
+      foo = 1;
+    };
+    nullableValue.list = [ { bar = [ 1 ]; } ]; # list
+    nullableValue.lambda = x: x; # Error
+
+    # mkStructuredType { nullable = false; }
+    structuredValue.null = null; # Error
+
     assertions =
       with lib.types;
 
@@ -486,6 +513,9 @@ in
       assert (unique { message = "custom"; } (listOf str)).description == "list of string";
       assert (unique { message = "test"; } (either int str)).description == "signed integer or string";
       assert (unique { message = "test"; } (listOf str)).description == "list of string";
+      # json & toml
+      assert json.description == "JSON value";
+      assert toml.description == "TOML value";
       # done
       "ok";
   };
diff --git a/lib/types.nix b/lib/types.nix
index bc6e28ed93639..711177a681411 100644
--- a/lib/types.nix
+++ b/lib/types.nix
@@ -1436,6 +1436,45 @@ let
           };
         };
 
+      /**
+        Creates a structured value type suitable for serialization formats.
+
+        Parameters:
+        - typeName: String describing the format (e.g. "JSON", "YAML", "XML")
+        - nullable: Whether the structured value type allows `null` values.
+
+        Returns a type suitable for structured data formats that supports:
+        - Basic types: boolean, integer, float, string, path
+        - Complex types: attribute sets and lists
+      */
+      mkStructuredType =
+        {
+          typeName,
+          nullable ? true,
+        }:
+        let
+          baseType = oneOf [
+            bool
+            int
+            float
+            str
+            path
+            (attrsOf valueType)
+            (listOf valueType)
+          ];
+          valueType = (if nullable then nullOr baseType else baseType) // {
+            description = "${typeName} value";
+          };
+        in
+        valueType;
+
+      json = mkStructuredType { typeName = "JSON"; };
+
+      toml = mkStructuredType {
+        typeName = "TOML";
+        nullable = false;
+      };
+
       # Either value of type `t1` or `t2`.
       either =
         t1: t2:
diff --git a/nixos/doc/manual/development/option-types.section.md b/nixos/doc/manual/development/option-types.section.md
index 707e2e3d13457..48dba62aabbca 100644
--- a/nixos/doc/manual/development/option-types.section.md
+++ b/nixos/doc/manual/development/option-types.section.md
@@ -497,6 +497,20 @@ Composed types are types that take a type as parameter. `listOf
     value of type *`to`*. Can be used to preserve backwards compatibility
     of an option if its type was changed.
 
+`types.json`
+
+:   A type representing JSON-compatible values. This includes `null`, booleans,
+    integers, floats, strings, paths, attribute sets, and lists.
+    Attribute sets and lists can be arbitrarily nested and contain any JSON-compatible
+    values.
+
+`types.toml`
+
+:   A type representing TOML-compatible values. This includes booleans,
+    integers, floats, strings, paths, attribute sets, and lists.
+    Attribute sets and lists can be arbitrarily nested and contain any TOML-compatible
+    values.
+
 ## Submodule {#section-option-types-submodule}
 
 `submodule` is a very powerful type that defines a set of sub-options
diff --git a/pkgs/pkgs-lib/formats.nix b/pkgs/pkgs-lib/formats.nix
index 14ca988e9c49a..2897b0201bf20 100644
--- a/pkgs/pkgs-lib/formats.nix
+++ b/pkgs/pkgs-lib/formats.nix
@@ -40,6 +40,7 @@ let
     ;
 
   inherit (lib.types)
+    mkStructuredType
     attrsOf
     atom
     bool
@@ -58,38 +59,6 @@ let
     submodule
     ;
 
-  /*
-    Creates a structured value type suitable for serialization formats.
-
-    Parameters:
-    - typeName: String describing the format (e.g. "JSON", "YAML", "XML")
-    - nullable: Whether the structured value type allows `null` values.
-
-    Returns a type suitable for structured data formats that supports:
-    - Basic types: boolean, integer, float, string, path
-    - Complex types: attribute sets and lists
-  */
-  mkStructuredType =
-    {
-      typeName,
-      nullable ? true,
-    }:
-    let
-      baseType = oneOf [
-        bool
-        int
-        float
-        str
-        path
-        (attrsOf valueType)
-        (listOf valueType)
-      ];
-      valueType = (if nullable then nullOr baseType else baseType) // {
-        description = "${typeName} value";
-      };
-    in
-    valueType;
-
   # Attributes added accidentally in https://github.com/NixOS/nixpkgs/pull/335232 (2024-08-18)
   # Deprecated in https://github.com/NixOS/nixpkgs/pull/415666 (2025-06)
   allowAliases = pkgs.config.allowAliases or false;
@@ -162,7 +131,7 @@ optionalAttrs allowAliases aliases
     { }:
     {
 
-      type = mkStructuredType { typeName = "JSON"; };
+      type = types.json;
 
       generate =
         name: value:
@@ -487,10 +456,7 @@ optionalAttrs allowAliases aliases
     { }:
     json { }
     // {
-      type = mkStructuredType {
-        typeName = "TOML";
-        nullable = false;
-      };
+      type = types.toml;
 
       generate =
         name: value: