diff --git a/mola_yaml/include/mola_yaml/yaml_helpers.h b/mola_yaml/include/mola_yaml/yaml_helpers.h
index 552beb3b..92a82c5e 100644
--- a/mola_yaml/include/mola_yaml/yaml_helpers.h
+++ b/mola_yaml/include/mola_yaml/yaml_helpers.h
@@ -14,7 +14,7 @@
 #include <mola_yaml/macro_helpers.h>
 #include <mrpt/containers/yaml.h>
 
-#include <sstream>
+#include <map>
 #include <string>
 
 namespace mola
@@ -27,7 +27,10 @@ struct YAMLParseOptions
 {
     bool doIncludes{true};  //!< "$include{}"s
     bool doCmdRuns{true};  //!< "$()"s
-    bool doEnvVars{true};  //!< "${}"s
+    bool doEnvVars{true};  //!< "${}"s (from env vars and field "variables")
+
+    /** Custom variables for replacements like `${name}` => `value` */
+    std::map<std::string, std::string> variables;
 
     /** If not empty, base reference path which respect to "$include{}"s are
      * specified. Automatically filled in by load_yaml_file() */
diff --git a/mola_yaml/src/yaml_helpers.cpp b/mola_yaml/src/yaml_helpers.cpp
index 9e8fed62..a5c08bf8 100644
--- a/mola_yaml/src/yaml_helpers.cpp
+++ b/mola_yaml/src/yaml_helpers.cpp
@@ -37,7 +37,9 @@ namespace fs = std::filesystem;
 
 using mrpt::containers::yaml;
 
-static std::string::size_type findClosing(
+namespace
+{
+std::string::size_type findClosing(
     size_t pos, const std::string& s, const char searchEndChar,
     const char otherStartChar)
 {
@@ -59,8 +61,7 @@ static std::string::size_type findClosing(
 }
 
 // "foo|bar" -> {"foo","bar"}
-static std::tuple<std::string, std::string> splitVerticalBar(
-    const std::string& s)
+std::tuple<std::string, std::string> splitVerticalBar(const std::string& s)
 {
     const auto posBar = s.find("|");
     if (posBar == std::string::npos) return {s, {}};
@@ -68,7 +69,7 @@ static std::tuple<std::string, std::string> splitVerticalBar(
     return {s.substr(0, posBar), s.substr(posBar + 1)};
 }
 
-static std::string trimWSNL(const std::string& s)
+std::string trimWSNL(const std::string& s)
 {
     std::string str = s;
     mrpt::system::trim(str);
@@ -76,6 +77,8 @@ static std::string trimWSNL(const std::string& s)
     str.erase(std::remove(str.begin(), str.end(), '\n'), str.end());
     return str;
 }
+}  // namespace
+
 std::string mola::yaml_to_string(const mrpt::containers::yaml& cfg)
 {
     std::stringstream ss;
@@ -83,7 +86,9 @@ std::string mola::yaml_to_string(const mrpt::containers::yaml& cfg)
     return ss.str();
 }
 
-static std::string parseEnvVars(
+namespace
+{
+std::string parseVars(
     const std::string& text, const mola::YAMLParseOptions& opts)
 {
     MRPT_TRY_START
@@ -106,30 +111,43 @@ static std::string parseEnvVars(
 
     const auto [varname, defaultValue] = splitVerticalBar(varnameOrg);
 
+    // 1st try:  match to env vars
     std::string varvalue;
     const char* v = ::getenv(varname.c_str());
     if (v != nullptr)
+    {  // match:
         varvalue = std::string(v);
+    }
     else
     {
-        // Handle special variable names:
+        // 2nd try: handle special variable names:
         // ${CURRENT_YAML_FILE_PATH}
         if (varname == "CURRENT_YAML_FILE_PATH")
             varvalue = opts.includesBasePath;
-        else if (!defaultValue.empty()) { varvalue = defaultValue; }
         else
-        {
-            THROW_EXCEPTION_FMT(
-                "YAML parseEnvVars(): Undefined environment variable: ${%s}",
-                varname.c_str());
-        }
+            // 3rd try: custom user variables
+            if (auto it = opts.variables.find(varname);
+                it != opts.variables.end())
+            {
+                varvalue = it->second;
+            }
+            else
+                // 4th: default:
+                if (!defaultValue.empty()) { varvalue = defaultValue; }
+                else
+                {
+                    THROW_EXCEPTION_FMT(
+                        "YAML parseEnvVars(): Undefined environment variable: "
+                        "${%s}",
+                        varname.c_str());
+                }
     }
 
-    return parseEnvVars(pre + varvalue + post.substr(post_end + 1), opts);
+    return parseVars(pre + varvalue + post.substr(post_end + 1), opts);
     MRPT_TRY_END
 }
 
-static std::string parseCmdRuns(
+std::string parseCmdRuns(
     const std::string& text, const mola::YAMLParseOptions& opts)
 {
     MRPT_TRY_START
@@ -167,7 +185,7 @@ static std::string parseCmdRuns(
     MRPT_TRY_END
 }
 
-static void recursiveParseNodeForIncludes(
+void recursiveParseNodeForIncludes(
     yaml::node_t& n, const mola::YAMLParseOptions& opts)
 {
     if (n.isScalar())
@@ -241,7 +259,7 @@ static void recursiveParseNodeForIncludes(
     }
 }
 
-static std::string parseIncludes(
+std::string parseIncludes(
     const std::string& text, const mola::YAMLParseOptions& opts)
 {
     MRPT_TRY_START
@@ -255,6 +273,8 @@ static std::string parseIncludes(
     MRPT_TRY_END
 }
 
+}  // namespace
+
 mrpt::containers::yaml mola::parse_yaml(
     const mrpt::containers::yaml& input, const mola::YAMLParseOptions& opts)
 {
@@ -274,7 +294,7 @@ std::string mola::parse_yaml(
     if (opts.doCmdRuns) s = parseCmdRuns(s, opts);
 
     // 3) Parse "${}"s
-    if (opts.doEnvVars) s = parseEnvVars(s, opts);
+    if (opts.doEnvVars) s = parseVars(s, opts);
 
     return s;
 }
diff --git a/mola_yaml/tests/test-yaml-parser.cpp b/mola_yaml/tests/test-yaml-parser.cpp
index f31977c5..39f4d92a 100644
--- a/mola_yaml/tests/test-yaml-parser.cpp
+++ b/mola_yaml/tests/test-yaml-parser.cpp
@@ -18,7 +18,9 @@
 
 using namespace std::string_literals;
 
-static void test_yaml2string()
+namespace
+{
+void test_yaml2string()
 {
     {
         const auto data = mrpt::containers::yaml::Map({{"A", 1.0}, {"B", 3}});
@@ -43,9 +45,10 @@ b: "foo"
   - c
 d:
   va: 'z'
+e: '${foo|default1}'
 )###";
 
-static void test_parseSimple()
+void test_parseSimple()
 {
     {
         const auto y = mrpt::containers::yaml::FromText(txt1);
@@ -57,7 +60,35 @@ static void test_parseSimple()
     }
 }
 
-static void test_parseIncludes()
+void test_parseCustomVars()
+{
+    {
+        const auto y = mola::parse_yaml(mrpt::containers::yaml::FromText(txt1));
+        ASSERT_(y.isMap());
+        ASSERT_EQUAL_(y["e"].as<std::string>(), "default1");
+    }
+    {
+        mola::YAMLParseOptions opts;
+        opts.doEnvVars = false;
+
+        const auto y =
+            mola::parse_yaml(mrpt::containers::yaml::FromText(txt1), opts);
+        ASSERT_(y.isMap());
+        ASSERT_EQUAL_(y["e"].as<std::string>(), "${foo|default1}");
+    }
+    {
+        mola::YAMLParseOptions opts;
+        const std::string      se = "Something Else";
+        opts.variables["foo"]     = se;
+
+        const auto y =
+            mola::parse_yaml(mrpt::containers::yaml::FromText(txt1), opts);
+        ASSERT_(y.isMap());
+        ASSERT_EQUAL_(y["e"].as<std::string>(), se);
+    }
+}
+
+void test_parseIncludes()
 {
     {
         const auto file = MOLA_MODULE_SOURCE_DIR + "/test_include1.yaml"s;
@@ -97,6 +128,8 @@ static void test_parseIncludes()
     }
 }
 
+}  // namespace
+
 MRPT_TODO("Possible bug: #$include{} shouldn't be parsed")
 MRPT_TODO("bug: #${var} shouldn't be parsed")
 
@@ -107,7 +140,7 @@ int main([[maybe_unused]] int argc, [[maybe_unused]] char** argv)
         test_yaml2string();
         test_parseSimple();
         test_parseIncludes();
-        // test_parseEnvSimple();
+        test_parseCustomVars();
 
         std::cout << "Test successful." << std::endl;
     }