diff --git a/libdevcore/Whiskers.cpp b/libdevcore/Whiskers.cpp
index a6db35c8e..8a20f2cd7 100644
--- a/libdevcore/Whiskers.cpp
+++ b/libdevcore/Whiskers.cpp
@@ -30,64 +30,73 @@
 using namespace std;
 using namespace dev;
 
-Whiskers::Whiskers(string const& _template):
-m_template(_template)
+Whiskers::Whiskers(string _template):
+	m_template(move(_template))
 {
 }
 
-Whiskers& Whiskers::operator ()(string const& _parameter, string const& _value)
+Whiskers& Whiskers::operator()(string _parameter, string _value)
 {
-	assertThrow(
-		m_parameters.count(_parameter) == 0,
-		WhiskersError,
-		_parameter + " already set."
-	);
-	assertThrow(
-		m_listParameters.count(_parameter) == 0,
-		WhiskersError,
-		_parameter + " already set as list parameter."
-	);
-	m_parameters[_parameter] = _value;
-
+	checkParameterUnknown(_parameter);
+	m_parameters[move(_parameter)] = move(_value);
 	return *this;
 }
 
-Whiskers& Whiskers::operator ()(
-	string const& _listParameter,
-	vector<map<string, string>> const& _values
+Whiskers& Whiskers::operator()(string _parameter, bool _value)
+{
+	checkParameterUnknown(_parameter);
+	m_conditions[move(_parameter)] = _value;
+	return *this;
+}
+
+Whiskers& Whiskers::operator()(
+	string _listParameter,
+	vector<map<string, string>> _values
 )
 {
-	assertThrow(
-		m_listParameters.count(_listParameter) == 0,
-		WhiskersError,
-		_listParameter + " already set."
-	);
-	assertThrow(
-		m_parameters.count(_listParameter) == 0,
-		WhiskersError,
-		_listParameter + " already set as value parameter."
-	);
-	m_listParameters[_listParameter] = _values;
-
+	checkParameterUnknown(_listParameter);
+	m_listParameters[move(_listParameter)] = move(_values);
 	return *this;
 }
 
 string Whiskers::render() const
 {
-	return replace(m_template, m_parameters, m_listParameters);
+	return replace(m_template, m_parameters, m_conditions, m_listParameters);
+}
+
+void Whiskers::checkParameterUnknown(string const& _parameter)
+{
+	assertThrow(
+		!m_parameters.count(_parameter),
+		WhiskersError,
+		_parameter + " already set as value parameter."
+	);
+	assertThrow(
+		!m_conditions.count(_parameter),
+		WhiskersError,
+		_parameter + " already set as condition parameter."
+	);
+	assertThrow(
+		!m_listParameters.count(_parameter),
+		WhiskersError,
+		_parameter + " already set as list parameter."
+	);
 }
 
 string Whiskers::replace(
 	string const& _template,
 	StringMap const& _parameters,
+	map<string, bool> const& _conditions,
 	map<string, vector<StringMap>> const& _listParameters
 )
 {
 	using namespace boost;
-	static regex listOrTag("<([^#/>]+)>|<#([^>]+)>(.*?)</\\2>");
+	static regex listOrTag("<([^#/?!>]+)>|<#([^>]+)>(.*?)</\\2>|<\\?([^>]+)>(.*?)(<!\\4>(.*?))?</\\4>");
 	return regex_replace(_template, listOrTag, [&](match_results<string::const_iterator> _match) -> string
 	{
 		string tagName(_match[1]);
+		string listName(_match[2]);
+		string conditionName(_match[4]);
 		if (!tagName.empty())
 		{
 			assertThrow(
@@ -99,20 +108,32 @@ string Whiskers::replace(
 			);
 			return _parameters.at(tagName);
 		}
-		else
+		else if (!listName.empty())
 		{
-			string listName(_match[2]);
 			string templ(_match[3]);
-			assertThrow(!listName.empty(), WhiskersError, "");
 			assertThrow(
 				_listParameters.count(listName),
 				WhiskersError, "List parameter " + listName + " not set."
 			);
 			string replacement;
 			for (auto const& parameters: _listParameters.at(listName))
-				replacement += replace(templ, joinMaps(_parameters, parameters));
+				replacement += replace(templ, joinMaps(_parameters, parameters), _conditions);
 			return replacement;
 		}
+		else
+		{
+			assertThrow(!conditionName.empty(), WhiskersError, "");
+			assertThrow(
+				_conditions.count(conditionName),
+				WhiskersError, "Condition parameter " + conditionName + " not set."
+			);
+			return replace(
+				_conditions.at(conditionName) ? _match[5] : _match[7],
+				_parameters,
+				_conditions,
+				_listParameters
+			);
+		}
 	});
 }
 
diff --git a/libdevcore/Whiskers.h b/libdevcore/Whiskers.h
index 21d46af4c..7944358a0 100644
--- a/libdevcore/Whiskers.h
+++ b/libdevcore/Whiskers.h
@@ -34,45 +34,63 @@ namespace dev
 
 DEV_SIMPLE_EXCEPTION(WhiskersError);
 
-///
-/// Moustache-like templates.
-///
-/// Usage:
-///     std::vector<std::map<std::string, std::string>> listValues(2);
-///     listValues[0]["k"] = "key1";
-///     listValues[0]["v"] = "value1";
-///     listValues[1]["k"] = "key2";
-///     listValues[1]["v"] = "value2";
-///     auto s = Whiskers("<p1>\n<#list><k> -> <v>\n</list>")
-///         ("p1", "HEAD")
-///         ("list", listValues)
-///         .render();
-///
-/// results in s == "HEAD\nkey1 -> value1\nkey2 -> value2\n"
-///
-/// Note that lists cannot themselves contain lists - this would be a future feature.
+/**
+ * Moustache-like templates.
+ *
+ * Usage:
+ *     std::vector<std::map<std::string, std::string>> listValues(2);
+ *     listValues[0]["k"] = "key1";
+ *     listValues[0]["v"] = "value1";
+ *     listValues[1]["k"] = "key2";
+ *     listValues[1]["v"] = "value2";
+ *     auto s = Whiskers("<?c><p1><!c>y</c>\n<#list><k> -> <v>\n</list>")
+ *         ("p1", "HEAD")
+ *         ("c", true)
+ *         ("list", listValues)
+ *         .render();
+ *
+ * results in s == "HEAD\nkey1 -> value1\nkey2 -> value2\n"
+ *
+ * Note that lists cannot themselves contain lists - this would be a future feature.
+ *
+ * The elements are:
+ *  - Regular parameter: <name>
+ *    just replaced
+ *  - Condition parameter: <?name>...<!name>...</name>, where "<!name>" is optional
+ *    replaced (and recursively expanded) by the first part if the condition is true
+ *    and by the second (or empty string if missing) if the condition is false
+ *  - List parameter: <#list>...</list>
+ *    The part between the tags is repeated as often as values are provided
+ *    in the mapping. Each list element can have its own parameter -> value mapping.
+ */
 class Whiskers
 {
 public:
 	using StringMap = std::map<std::string, std::string>;
 	using StringListMap = std::map<std::string, std::vector<StringMap>>;
 
-	explicit Whiskers(std::string const& _template);
+	explicit Whiskers(std::string _template);
 
-	/// Sets a single parameter, <paramName>.
-	Whiskers& operator()(std::string const& _parameter, std::string const& _value);
+	/// Sets a single regular parameter, <paramName>.
+	Whiskers& operator()(std::string _parameter, std::string _value);
+	Whiskers& operator()(std::string _parameter, char const* _value) { return (*this)(_parameter, std::string{_value}); }
+	/// Sets a condition parameter, <?paramName>...<!paramName>...</paramName>
+	Whiskers& operator()(std::string _parameter, bool _value);
 	/// Sets a list parameter, <#listName> </listName>.
 	Whiskers& operator()(
-		std::string const& _listParameter,
-		std::vector<StringMap> const& _values
+		std::string _listParameter,
+		std::vector<StringMap> _values
 	);
 
 	std::string render() const;
 
 private:
+	void checkParameterUnknown(std::string const& _parameter);
+
 	static std::string replace(
 		std::string const& _template,
 		StringMap const& _parameters,
+		std::map<std::string, bool> const& _conditions,
 		StringListMap const& _listParameters = StringListMap()
 	);
 
@@ -81,6 +99,7 @@ private:
 
 	std::string m_template;
 	StringMap m_parameters;
+	std::map<std::string, bool> m_conditions;
 	StringListMap m_listParameters;
 };
 
diff --git a/test/libdevcore/Whiskers.cpp b/test/libdevcore/Whiskers.cpp
index b12acdd70..8a785774e 100644
--- a/test/libdevcore/Whiskers.cpp
+++ b/test/libdevcore/Whiskers.cpp
@@ -55,6 +55,65 @@ BOOST_AUTO_TEST_CASE(tag_unavailable)
 	BOOST_CHECK_THROW(m.render(), WhiskersError);
 }
 
+BOOST_AUTO_TEST_CASE(list_unavailable)
+{
+	string templ = "<#b></b>";
+	Whiskers m(templ);
+	BOOST_CHECK_THROW(m.render(), WhiskersError);
+}
+
+BOOST_AUTO_TEST_CASE(name_type_collision)
+{
+	string templ = "<b><#b></b>";
+	Whiskers m(templ);
+	m("b", "x");
+	BOOST_CHECK_THROW(m("b", vector<map<string, string>>{}), WhiskersError);
+}
+
+BOOST_AUTO_TEST_CASE(conditional)
+{
+	string templ = "<?b>X</b>";
+	BOOST_CHECK_EQUAL(Whiskers(templ)("b", true).render(), "X");
+	BOOST_CHECK_EQUAL(Whiskers(templ)("b", false).render(), "");
+}
+
+BOOST_AUTO_TEST_CASE(conditional_with_else)
+{
+	string templ = "<?b>X<!b>Y</b>";
+	BOOST_CHECK_EQUAL(Whiskers(templ)("b", true).render(), "X");
+	BOOST_CHECK_EQUAL(Whiskers(templ)("b", false).render(), "Y");
+}
+
+BOOST_AUTO_TEST_CASE(conditional_plus_params)
+{
+	string templ = " - <?b>_<r><!b>^<t></b> - ";
+	Whiskers m1(templ);
+	m1("b", true);
+	m1("r", "R");
+	m1("t", "T");
+	BOOST_CHECK_EQUAL(m1.render(), " - _R - ");
+
+	Whiskers m2(templ);
+	m2("b", false);
+	m2("r", "R");
+	m2("t", "T");
+	BOOST_CHECK_EQUAL(m2.render(), " - ^T - ");
+}
+
+BOOST_AUTO_TEST_CASE(conditional_plus_list)
+{
+	string templ = " - <?b>_<#l><x></l><!b><#l><y></l></b> - ";
+	Whiskers m(templ);
+	m("b", false);
+	vector<map<string, string>> list(2);
+	list[0]["x"] = "1";
+	list[0]["y"] = "a";
+	list[1]["x"] = "2";
+	list[1]["y"] = "b";
+	m("l", list);
+	BOOST_CHECK_EQUAL(m.render(), " - ab - ");
+}
+
 BOOST_AUTO_TEST_CASE(complicated_replacement)
 {
 	string templ = "a <b> x <complicated> \n <nes<ted>>.";