diff --git a/CMakeLists_files.cmake b/CMakeLists_files.cmake
index aa6e2d520..c404ccc13 100644
--- a/CMakeLists_files.cmake
+++ b/CMakeLists_files.cmake
@@ -403,6 +403,7 @@ list (APPEND TEST_SOURCE_FILES
   tests/test_partitionCells.cpp
   tests/test_preconditionerfactory.cpp
   tests/test_privarspacking.cpp
+  tests/test_propertytree.cpp
   tests/test_region_phase_pvaverage.cpp
   tests/test_relpermdiagnostics.cpp
   tests/test_RestartSerialization.cpp
diff --git a/opm/simulators/linalg/PropertyTree.cpp b/opm/simulators/linalg/PropertyTree.cpp
index 96d43e674..81952839d 100644
--- a/opm/simulators/linalg/PropertyTree.cpp
+++ b/opm/simulators/linalg/PropertyTree.cpp
@@ -23,8 +23,14 @@
 
 #include <boost/property_tree/json_parser.hpp>
 
-namespace Opm
-{
+#include <memory>
+#include <optional>
+#include <ostream>
+#include <string>
+
+#include <stddef.h>
+
+namespace Opm {
 
 PropertyTree::PropertyTree()
     : tree_(std::make_unique<boost::property_tree::ptree>())
@@ -96,23 +102,23 @@ PropertyTree& PropertyTree::operator=(const PropertyTree& tree)
   return *this;
 }
 
-template std::string PropertyTree::get<std::string>(const std::string& key) const;
-template std::string PropertyTree::get<std::string>(const std::string& key, const std::string& defValue) const;
-template double PropertyTree::get<double>(const std::string& key) const;
-template double PropertyTree::get<double>(const std::string& key, const double& defValue) const;
-template float PropertyTree::get<float>(const std::string& key) const;
-template float PropertyTree::get<float>(const std::string& key, const float& defValue) const;
-template int PropertyTree::get<int>(const std::string& key) const;
-template int PropertyTree::get<int>(const std::string& key, const int& defValue) const;
-template size_t PropertyTree::get<size_t>(const std::string& key) const;
-template size_t PropertyTree::get<size_t>(const std::string& key, const size_t& defValue) const;
-template bool PropertyTree::get<bool>(const std::string& key) const;
-template bool PropertyTree::get<bool>(const std::string& key, const bool& defValue) const;
+template std::string PropertyTree::get(const std::string& key) const;
+template double PropertyTree::get(const std::string& key) const;
+template float PropertyTree::get(const std::string& key) const;
+template int PropertyTree::get(const std::string& key) const;
+template size_t PropertyTree::get(const std::string& key) const;
+template bool PropertyTree::get(const std::string& key) const;
 
-template void PropertyTree::put<std::string>(const std::string& key, const std::string& value);
-template void PropertyTree::put<float>(const std::string& key, const float& value);
-template void PropertyTree::put<double>(const std::string& key, const double& value);
-template void PropertyTree::put<int>(const std::string& key, const int& value);
+template std::string PropertyTree::get(const std::string& key, const std::string& defValue) const;
+template double PropertyTree::get(const std::string& key, const double& defValue) const;
+template float PropertyTree::get(const std::string& key, const float& defValue) const;
+template int PropertyTree::get(const std::string& key, const int& defValue) const;
+template size_t PropertyTree::get(const std::string& key, const size_t& defValue) const;
+template bool PropertyTree::get(const std::string& key, const bool& defValue) const;
 
+template void PropertyTree::put(const std::string& key, const std::string& value);
+template void PropertyTree::put(const std::string& key, const float& value);
+template void PropertyTree::put(const std::string& key, const double& value);
+template void PropertyTree::put(const std::string& key, const int& value);
 
 } // namespace Opm
diff --git a/opm/simulators/linalg/PropertyTree.hpp b/opm/simulators/linalg/PropertyTree.hpp
index 3c32b2227..2799eac16 100644
--- a/opm/simulators/linalg/PropertyTree.hpp
+++ b/opm/simulators/linalg/PropertyTree.hpp
@@ -20,51 +20,136 @@
 #ifndef OPM_PROPERTYTREE_HEADER_INCLUDED
 #define OPM_PROPERTYTREE_HEADER_INCLUDED
 
+#include <functional>
 #include <iosfwd>
 #include <memory>
 #include <optional>
+#include <string>
 
-namespace boost {
-namespace property_tree {
+namespace boost::property_tree {
     template<class T1, class T2, class T3> class basic_ptree;
-    using ptree = basic_ptree<std::string,std::string,std::less<std::string>>;
-}
-}
+    using ptree = basic_ptree<std::string, std::string, std::less<std::string>>;
+} // namespace boost::property_tree
 
-namespace Opm
+namespace Opm {
+
+/// Hierarchical collection of key/value pairs
+class PropertyTree
 {
-
-class PropertyTree {
 public:
+    /// Default constructor.
+    ///
+    /// Should typically be populated in put() before use.
     PropertyTree();
+
+    /// Constructor
+    ///
+    /// Loads a property tree from an external source expected to be a text
+    /// file in JSON.
+    ///
+    /// \param[in] jsonFile Name of file containing external property tree,
+    /// linearised into JSON format.
     explicit PropertyTree(const std::string& jsonFile);
+
+    /// Copy constructor.
+    ///
+    /// \param[in] tree Source object.
     PropertyTree(const PropertyTree& tree);
+
+    /// Destructor.
     ~PropertyTree();
 
+    /// Assignment operator
+    ///
+    /// \param[in] tree Source object.
+    ///
+    /// \return \code *this \endcode.
+    PropertyTree& operator=(const PropertyTree& tree);
+
+    /// Insert key/value pair into property tree
+    ///
+    /// \tparam T Value type
+    ///
+    /// \param[in] key Property key.  Expected to be in hierarchical
+    /// notation for subtrees--i.e., using periods ('.') to separate
+    /// hierarchy levels.
+    ///
+    /// \param[in] data Property value corresponding to \p key.
     template<class T>
     void put(const std::string& key, const T& data);
 
+    /// Retrieve property value given hierarchical property key.
+    ///
+    /// \tparam T Value type
+    ///
+    /// \param[in] key Property key.  Expected to be in hierarchical
+    /// notation for subtrees--i.e., using periods ('.') to separate
+    /// hierarchy levels.
+    ///
+    /// \return Copy of internal property value for \p key.
     template<class T>
     T get(const std::string& key) const;
 
+    /// Retrieve property value given hierarchical property key.
+    ///
+    /// \tparam T Value type
+    ///
+    /// \param[in] key Property key.  Expected to be in hierarchical
+    /// notation for subtrees--i.e., using periods ('.') to separate
+    /// hierarchy levels.
+    ///
+    /// \param[in] defValue Default value for when \p key is not in the
+    /// property tree.
+    ///
+    /// \return Copy of internal property value for \p key, or a copy of \p
+    /// defValue if the \p key is not in the property tree.
     template<class T>
     T get(const std::string& key, const T& defValue) const;
 
+    /// Retrieve copy of sub tree rooted at node.
+    ///
+    /// Throws an exception if no sub tree exists at given root.
+    ///
+    /// \param[in] Property key.  Expected to be in hierarchical
+    /// notation for subtrees--i.e., using periods ('.') to separate
+    /// hierarchy levels.
+    ///
+    /// \return Copy of property sub tree rooted at \p key.
     PropertyTree get_child(const std::string& key) const;
 
-    std::optional<PropertyTree> get_child_optional(const std::string& key) const;
-
-    PropertyTree& operator=(const PropertyTree& tree);
+    /// Retrieve copy of sub tree rooted at node.
+    ///
+    /// \param[in] Property key.  Expected to be in hierarchical
+    /// notation for subtrees--i.e., using periods ('.') to separate
+    /// hierarchy levels.
+    ///
+    /// \return Copy of property sub tree rooted at \p key.  Nullopt if no
+    /// sub tree exists that is rooted at \p key.
+    std::optional<PropertyTree>
+    get_child_optional(const std::string& key) const;
 
+    /// Emit a textual representation of the property tree in JSON form
+    ///
+    /// \param[in,out] os Output stream.  Typically a stream opened on a
+    /// file.
+    ///
+    /// \param[in] pretty Whether or not to pretty-print the JSON
+    /// output--i.e., whether or not to insert new lines and spaces for
+    /// human readability.
     void write_json(std::ostream& os, bool pretty) const;
 
 protected:
+    /// Converting constructor.
+    ///
+    /// Forms a property tree object from a Boost ptree.
+    ///
+    /// \param[in] tree Source object represented as a Boost ptree.
     PropertyTree(const boost::property_tree::ptree& tree);
 
+    /// Internal representation of the property tree.
     std::unique_ptr<boost::property_tree::ptree> tree_;
 };
 
-
 } // namespace Opm
 
 #endif // OPM_PROPERTYTREE_HEADER_INCLUDED
diff --git a/tests/test_propertytree.cpp b/tests/test_propertytree.cpp
new file mode 100644
index 000000000..ac8ab04f6
--- /dev/null
+++ b/tests/test_propertytree.cpp
@@ -0,0 +1,245 @@
+/*
+  Copyright 2025 SINTEF Digital, Mathematics and Cybernetics.
+
+  This file is part of the Open Porous Media project (OPM).
+
+  OPM is free software: you can redistribute it and/or modify
+  it under the terms of the GNU General Public License as published by
+  the Free Software Foundation, either version 3 of the License, or
+  (at your option) any later version.
+
+  OPM is distributed in the hope that it will be useful,
+  but WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+  GNU General Public License for more details.
+
+  You should have received a copy of the GNU General Public License
+  along with OPM.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+#include <config.h>
+
+#define BOOST_TEST_MODULE TestPropertyTree
+
+#ifndef HAVE_MPI
+// Suppress GCC diagnostics of the form
+//
+//   warning: "HAVE_MPI" is not defined, evaluates to 0
+//
+// when compiling with "-Wundef".
+#define HAVE_MPI 0
+#endif  // HAVE_MPI
+
+#include <boost/test/unit_test.hpp>
+
+#include <opm/simulators/linalg/PropertyTree.hpp>
+
+#include <opm/common/utility/FileSystem.hpp>
+
+#include <filesystem>
+#include <fstream>
+#include <ios>
+#include <stdexcept>
+#include <string>
+#include <string_view>
+#include <vector>
+
+BOOST_AUTO_TEST_SUITE(Put_And_Get)
+
+BOOST_AUTO_TEST_CASE(Top_Node_Only)
+{
+    auto t = Opm::PropertyTree{};
+
+    t.put("a", 1234);
+    t.put("b", 123.4);
+    t.put("c", std::string { "hello" });
+    t.put("d", 12.34f);
+
+    {
+        const auto a = t.get<int>("a");
+        BOOST_CHECK_EQUAL(a, 1234);
+
+        const auto aa = t.get<int>("aa", 42);
+        BOOST_CHECK_EQUAL(aa, 42);
+    }
+
+    {
+        const auto b = t.get<double>("b");
+        BOOST_CHECK_CLOSE(b, 123.4, 1.0e-8);
+
+        const auto bb = t.get("bb", 2.71828);
+        BOOST_CHECK_CLOSE(bb, 2.71828, 1.0e-8);
+    }
+
+    {
+        const auto c = t.get<std::string>("c");
+        BOOST_CHECK_EQUAL(c, "hello");
+
+        const auto cc = t.get("cc", std::string { "world" });
+        BOOST_CHECK_EQUAL(cc, "world");
+    }
+
+    {
+        const auto d = t.get<float>("d");
+        BOOST_CHECK_CLOSE(d, 12.34f, 1.0e-6f);
+
+        const auto dd = t.get("dd", -1.618f);
+        BOOST_CHECK_CLOSE(dd, -1.618f, 1.0e-6f);
+    }
+}
+
+BOOST_AUTO_TEST_CASE(Missing_Keys)
+{
+    auto t = Opm::PropertyTree{};
+
+    BOOST_CHECK_THROW(t.get<int>("a"), std::exception);
+}
+
+BOOST_AUTO_TEST_CASE(Hierarchy)
+{
+    auto t = Opm::PropertyTree{};
+
+    t.put("a.b.c", 123);
+
+    {
+        const auto c = t.get<int>("a.b.c");
+        BOOST_CHECK_EQUAL(c, 123);
+    }
+
+    {
+        const auto a = t.get_child("a");
+        const auto c = a.get<int>("b.c");
+        BOOST_CHECK_EQUAL(c, 123);
+    }
+
+    {
+        const auto a = t.get_child("a");
+        const auto b = a.get_child("b");
+        const auto c = b.get<int>("c");
+        BOOST_CHECK_EQUAL(c, 123);
+        BOOST_CHECK_CLOSE(a.get<double>("b.d", 3.1415), 3.1415, 1.0e-8);
+    }
+
+    {
+        const auto f = t.get_child_optional("d.e.f");
+        BOOST_CHECK_MESSAGE(! f.has_value(), R"(Node "f" must not exist)");
+    }
+}
+
+BOOST_AUTO_TEST_SUITE_END() // Put_And_Get
+
+// ---------------------------------------------------------------------------
+
+BOOST_AUTO_TEST_SUITE(Load_From_File)
+
+namespace {
+
+    class TempFile
+    {
+    public:
+        TempFile()
+            : fname_ { std::filesystem::temp_directory_path() /
+                       Opm::unique_path("wrk-%%%%") }
+        {}
+
+        ~TempFile()
+        {
+            std::filesystem::remove_all(this->fname_);
+        }
+
+        void append(std::string_view s)
+        {
+            std::ofstream { this->fname_, std::ios::app } << s;
+        }
+
+        std::string name() const
+        {
+            return this->fname_.generic_string();
+        }
+
+    private:
+        std::filesystem::path fname_;
+    };
+
+} // Anonymous namespace
+
+BOOST_AUTO_TEST_CASE(Top_Node_Only)
+{
+    auto f = TempFile{};
+    f.append(R"({
+ "a" : 1234,
+ "b" : 123.4,
+ "c" : "hello",
+ "d" : 12.34
+}
+)");
+
+    const auto t = Opm::PropertyTree { f.name() };
+    {
+        const auto a = t.get<int>("a");
+        BOOST_CHECK_EQUAL(a, 1234);
+
+        const auto aa = t.get<int>("aa", 42);
+        BOOST_CHECK_EQUAL(aa, 42);
+    }
+
+    {
+        const auto b = t.get<double>("b");
+        BOOST_CHECK_CLOSE(b, 123.4, 1.0e-8);
+
+        const auto bb = t.get("bb", 2.71828);
+        BOOST_CHECK_CLOSE(bb, 2.71828, 1.0e-8);
+    }
+
+    {
+        const auto c = t.get<std::string>("c");
+        BOOST_CHECK_EQUAL(c, "hello");
+
+        const auto cc = t.get("cc", std::string { "world" });
+        BOOST_CHECK_EQUAL(cc, "world");
+    }
+
+    {
+        const auto d = t.get<float>("d");
+        BOOST_CHECK_CLOSE(d, 12.34f, 1.0e-6f);
+
+        const auto dd = t.get("dd", -1.618f);
+        BOOST_CHECK_CLOSE(dd, -1.618f, 1.0e-6f);
+    }
+}
+
+BOOST_AUTO_TEST_CASE(Hierarchy)
+{
+    auto f = TempFile{};
+    f.append(R"({
+ "a" : { "b" : { "c" : 123 } }
+}
+)");
+
+    const auto t = Opm::PropertyTree { f.name() };
+    {
+        const auto c = t.get<int>("a.b.c");
+        BOOST_CHECK_EQUAL(c, 123);
+    }
+
+    {
+        const auto a = t.get_child("a");
+        const auto c = a.get<int>("b.c");
+        BOOST_CHECK_EQUAL(c, 123);
+    }
+
+    {
+        const auto a = t.get_child("a");
+        const auto b = a.get_child("b");
+        const auto c = b.get<int>("c");
+        BOOST_CHECK_EQUAL(c, 123);
+        BOOST_CHECK_CLOSE(a.get<double>("b.d", 3.1415), 3.1415, 1.0e-8);
+    }
+
+    {
+        const auto d_e_f = t.get_child_optional("d.e.f");
+        BOOST_CHECK_MESSAGE(! d_e_f.has_value(), R"(Node "f" must not exist)");
+    }
+}
+
+BOOST_AUTO_TEST_SUITE_END() // Load_From_File