diff --git a/test/tools/ossfuzz/SolCustomMutator.cpp b/test/tools/ossfuzz/SolCustomMutator.cpp
new file mode 100644
index 000000000..f6707b0cc
--- /dev/null
+++ b/test/tools/ossfuzz/SolCustomMutator.cpp
@@ -0,0 +1,88 @@
+/*
+	This file is part of solidity.
+
+	solidity 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.
+
+	solidity 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 solidity.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+#include <test/tools/ossfuzz/SolCustomMutator.h>
+
+#include <antlr4-runtime.h>
+#include <cstring>
+
+using namespace std;
+using namespace antlr4;
+using namespace solidity::test::fuzzer;
+
+namespace {
+/// Forward declare libFuzzer's default mutator definition
+extern "C" size_t LLVMFuzzerMutate(uint8_t* _data, size_t _size, size_t _maxSize);
+
+/// Define Solidity's custom mutator by implementing libFuzzer's
+/// custom mutator external interface.
+extern "C" size_t LLVMFuzzerCustomMutator(
+	uint8_t* _data,
+	size_t _size,
+	size_t _maxSize,
+	unsigned int _seed
+)
+{
+	if (_maxSize <= _size || _size == 0)
+		return LLVMFuzzerMutate(_data, _size, _maxSize);
+	return SolCustomMutator{_data, _size, _maxSize, _seed}.mutate();
+}
+}
+
+SolCustomMutator::SolCustomMutator(uint8_t* _data, size_t _size, size_t _maxSize, unsigned int _seed)
+{
+	Data = _data;
+	Size = _size;
+	In = string(_data, _data + _size),
+	MaxMutantSize = _maxSize;
+	Seed = _seed;
+}
+
+size_t SolCustomMutator::mutate()
+{
+	try
+	{
+		antlr4::ANTLRInputStream AStream(In);
+		SolidityLexer Lexer(&AStream);
+		Lexer.removeErrorListeners();
+		antlr4::CommonTokenStream Tokens(&Lexer);
+		Tokens.fill();
+		SolidityParser Parser(&Tokens);
+		Parser.removeErrorListeners();
+		SolidityMutator Mutator(Seed);
+		Parser.sourceUnit()->accept(&Mutator);
+		Out = Mutator.toString();
+
+		// If mutant is empty, default to libFuzzer's mutator
+		if (Out.empty())
+			return Size;
+		else
+		{
+			size_t mutantSize = Out.size() >= MaxMutantSize ? MaxMutantSize - 1 : Out.size();
+			fill_n(Data, MaxMutantSize, 0);
+			copy(Out.data(), Out.data() + mutantSize, Data);
+			return mutantSize;
+		}
+	}
+	// Range error is thrown by antlr4 runtime's ANTLRInputStream
+	// See https://github.com/antlr/antlr4/issues/2036
+	catch (range_error const&)
+	{
+		// Default to libFuzzer's mutator
+		return Size;
+	}
+}
diff --git a/test/tools/ossfuzz/SolCustomMutator.h b/test/tools/ossfuzz/SolCustomMutator.h
new file mode 100644
index 000000000..d62f5643d
--- /dev/null
+++ b/test/tools/ossfuzz/SolCustomMutator.h
@@ -0,0 +1,43 @@
+/*
+	This file is part of solidity.
+
+	solidity 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.
+
+	solidity 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 solidity.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+#pragma once
+
+#include <test/tools/ossfuzz/SolidityLexer.h>
+#include <test/tools/ossfuzz/SolidityMutator.h>
+#include <test/tools/ossfuzz/SolidityParser.h>
+
+#include <cstddef>
+#include <cstdint>
+#include <ostream>
+#include <random>
+
+namespace solidity::test::fuzzer
+{
+struct SolCustomMutator
+{
+	SolCustomMutator(uint8_t* _data, size_t _size, size_t _maxSize, unsigned _seed);
+	size_t mutate();
+
+	uint8_t* Data = nullptr;
+	size_t Size = 0;
+	std::string In{};
+	std::string Out{};
+	size_t MaxMutantSize = 0;
+	unsigned int Seed = 0;
+};
+}
\ No newline at end of file
diff --git a/test/tools/ossfuzz/SolidityMutator.cpp b/test/tools/ossfuzz/SolidityMutator.cpp
index b588c36e3..e8862c3eb 100644
--- a/test/tools/ossfuzz/SolidityMutator.cpp
+++ b/test/tools/ossfuzz/SolidityMutator.cpp
@@ -16,44 +16,766 @@
 */
 // SPDX-License-Identifier: GPL-3.0
 
+#include <libsolutil/Common.h>
+
 #include <test/tools/ossfuzz/SolidityMutator.h>
 
+#include <boost/algorithm/string/join.hpp>
+
 #include <algorithm>
+#include <regex>
 
 using namespace std;
 using namespace solidity::util;
 using namespace solidity::test::fuzzer;
+using SolP = solidity::test::fuzzer::SolidityParser;
 
-antlrcpp::Any SolidityMutator::visitSourceUnit(SolidityParser::SourceUnitContext* _ctx)
+string Generator::operator()(std::string&& _template, std::map<std::string, std::string>&& _args)
 {
-	if (_ctx->pragmaDirective().empty())
-		m_out << Whiskers(s_pragmaDirective)("directive", "experimental SMTChecker").render();
-	else
-		visitChildren(_ctx);
+	Whiskers w(move(_template));
+	for (auto &&item: _args)
+		w(move(item.first), move(item.second));
+	return w.render();
+}
+
+template <typename T>
+void SolidityMutator::fuzzRule(T* _ctx)
+{
+	mutate(_ctx);
+//	if (coinToss())
+//		gen();
+}
+
+void SolidityMutator::gen()
+{
+	static const vector<string> validPragmas = {
+		"experimental SMTChecker",
+		"experimental ABIEncoderV2"
+	};
+	m_out << generator(
+		[&]() {
+			return Whiskers(R"(pragma <string>;)")
+				("string", validPragmas[m_rand() % validPragmas.size()])
+				.render();
+		},
+		randOneToN(s_maxPragmas),
+		"\n",
+		true
+	);
+}
+
+void SolidityMutator::mutate(SolP::PragmaDirectiveContext*)
+{
+	m_out << Whiskers(R"(pragma <mutation>;)")
+		("mutation", mutatePragma())
+		.render();
+}
+
+string SolidityMutator::eventParam()
+{
+	return Whiskers(R"(<typename> <indexed> <id>)")
+		("typename", typeName())
+		("indexed", coinToss() ? "indexed" : "")
+		("id", coinToss() ? genRandomId("ev"): "")
+		.render();
+}
+
+string SolidityMutator::visibility()
+{
+	if (interfaceScope())
+		return "external";
+
+	switch (randOneToN(4))
+	{
+	case 1:
+		return "public";
+	case 2:
+		return "external";
+	case 3:
+		return "private";
+	case 4:
+		return "internal";
+	}
+	assert(false);
+}
+
+string SolidityMutator::mutability()
+{
+	switch (randOneToN(4))
+	{
+	case 1:
+		return "view";
+	case 2:
+		return "pure";
+	case 3:
+		if (libraryScope() || globalScope())
+			return "";
+		else
+			return "payable";
+	case 4:
+		return "";
+	}
+	assert(false);
+}
+
+string SolidityMutator::elementaryType(bool _allowAddressPayable)
+{
+	switch (randOneToN(8))
+	{
+	case 1:
+		return "address";
+	case 2:
+		if (_allowAddressPayable)
+			return "address payable";
+		else
+			return "address";
+	case 3:
+		return "bool";
+	case 4:
+		return "string";
+	case 5:
+		return "bytes";
+	case 6:
+		return "int" + bitWidth();
+	case 7:
+		return "uint" + bitWidth();
+	case 8:
+		return "bytes" + byteWidth();
+	}
+	assert(false);
+}
+
+string SolidityMutator::typeName()
+{
+	switch (randOneToN(5))
+	{
+	case 1:
+		// TODO: Implement function type mutator
+		return "function () external view returns (uint)";
+	case 2:
+		return Whiskers(R"(mapping (<keyType> => <typeName>))")
+			("keyType", elementaryType(false))
+			("typeName", typeName())
+			.render();
+	case 3:
+		if (m_numStructs > 0)
+			return "s" + to_string(m_rand() % m_numStructs);
+		else
+			return elementaryType();
+	case 4:
+		// TODO: Implement complex types
+		return "int[]";
+	case 5:
+		return elementaryType();
+	}
+	assert(false);
+}
+
+string SolidityMutator::dataLocation()
+{
+	switch (randOneToN(3))
+	{
+	case 1:
+		return "storage";
+	case 2:
+		return "memory";
+	case 3:
+		return "calldata";
+	}
+	assert(false);
+}
+
+template <class C>
+antlrcpp::Any SolidityMutator::genericVisitor(C* _ctx, std::string _ctxName)
+{
+	visitChildren(_ctx);
 	return antlrcpp::Any();
 }
 
-antlrcpp::Any SolidityMutator::visitPragmaDirective(SolidityParser::PragmaDirectiveContext*)
+string SolidityMutator::genRandomUserDefinedTypeName(unsigned _numIds, unsigned _len, char _start, char _end)
 {
-	auto PickLiteral = [&]() -> string
-	{
-		static const vector<string> alphanum = {
-			"0",
-			"experimental",
-			"solidity < 142857",
-			"solidity >=0.0.0",
-			"solidity >=0.0.0 <0.8.0",
-			"experimental __test",
-			"experimental SMTChecker",
-			"experimental ABIEncoderV2",
-			"experimental \"xyz\""
-		};
+	uniform_int_distribution<char> dist(_start, _end);
+	vector<string> ids{};
+	generate_n(back_inserter(ids), m_rand() % _numIds + 1, [&](){ return genRandString(_len, _start, _end); });
+	return boost::algorithm::join(ids, ".");
+}
 
-		return alphanum[randomOneToN(alphanum.size()) - 1];
+string SolidityMutator::genRandString(unsigned int _maxLen, char _start, char _end)
+{
+	uniform_int_distribution<char> dist(_start, _end);
+	string result{};
+	generate_n(back_inserter(result), m_rand() % _maxLen + 1, [&]{ return dist(m_rand); });
+	return result;
+}
+
+template <typename T, typename F, typename... Args>
+void SolidityMutator::visitItemsOrGenerate(T _container, F&& _generator, Args&&... _args)
+{
+	if (_container.size() == 0)
+		mayRun(forward<F>(_generator), forward<Args>(_args)...);
+	else
+		for (auto item: _container)
+			item->accept(this);
+}
+
+template <typename F, typename... Args>
+auto SolidityMutator::mayRun(F&& _func, Args&&... _args, unsigned _n)
+{
+	if (m_rand() % _n == 0)
+		return invoke(forward<F>(_func), forward<Args>(_args)...);
+	else
+		return result_of<F>::type();
+}
+
+antlrcpp::Any SolidityMutator::visitSourceUnit(SolP::SourceUnitContext* _ctx)
+{
+//	for (auto &item: _ctx->getRuleContexts<SolP::SourceUnitContext>())
+//		visitItemsOrGenerate(item, gen, this, item);
+
+//	mayRun(
+//		[](SolP::SourceUnitContext* _ctx) {
+//			visitItemsOrGenerate(
+//				_ctx->pragmaDirective(),
+//				[&]() {	m_out << "pragma solidity >= 0.0.0;"; }
+//			);
+//			visitItemsOrGenerate(
+//				_ctx->importDirective(),
+//				[]() {}
+//			);
+//			visitItemsOrGenerate(
+//				_ctx->contractDefinition(),
+//				[&]() { genContract(); }
+//			);
+//			visitItemsOrGenerate(
+//				_ctx->interfaceDefinition(),
+//				[&]() {
+//					m_out << Whiskers(R"(interface <id> { function f0() external; })")
+//						("id", "I" + to_string(m_numInterfaces++))
+//						.render();
+//				}
+//			);
+//			visitItemsOrGenerate(
+//			  _ctx->libraryDefinition(),
+//			  [&]() {
+//				m_out << Whiskers(R"(library <id> { function f0() public {} })")
+//					("id", "L" + to_string(m_numLibraries++))
+//					.render();
+//			  }
+//			);
+//			visitItemsOrGenerate(
+//			  _ctx->functionDefinition(),
+//			  [&]() {
+//				m_out << "function func() {}";
+//			  }
+//			);
+//			visitItemsOrGenerate(
+//			  _ctx->structDefinition(),
+//			  [&]() {
+//				m_out << "struct S { uint sm0; }";
+//			  }
+//			);
+//			visitItemsOrGenerate(
+//			  _ctx->enumDefinition(),
+//			  [&]() {
+//				m_out << "enum E { first }";
+//			  }
+//			);
+//		}
+//	);
+
+
+	return antlrcpp::Any();
+}
+
+//void SolidityMutator::gen(SolP::ModifierDefinitionContext*)
+//{
+//	constexpr string s = R"(modifier <id> (<params>) <virtual> <override> <?noDef>;</noDef>)";
+//	Whiskers mod(R"(modifier <id> (<params>) <virtual> <override> <?noDef>;</noDef>)");
+//}
+//
+//void SolidityMutator::mutate(SolP::ModifierDefinitionContext* _ctx)
+//{
+//	for (auto &rule: _ctx->getRuleContexts<SolP::ModifierDefinitionContext>())
+//		std::cout << rule->getText() << std::endl;
+//}
+
+antlrcpp::Any SolidityMutator::visitModifierDefinition(SolidityParser::ModifierDefinitionContext* _ctx)
+{
+	Whiskers mod(R"(modifier <id> (<params>) <virtual> <override> <?noDef>;</noDef>)");
+
+	bool noDef = coinToss();
+	m_out << mod
+		("id", genRandomId("m", 2))
+		("params", _ctx->arguments ? _ctx->arguments->accept(this).as<string>() : "")
+		("virtual", coinToss() ? "virtual" : "")
+		("override", coinToss() ? "override" : "")
+		("noDef", noDef)
+		.render();
+	if (!noDef && _ctx->body)
+		_ctx->body->accept(this);
+	return antlrcpp::Any();
+}
+
+antlrcpp::Any SolidityMutator::visitStructDefinition(SolP::StructDefinitionContext* _ctx)
+{
+	Whiskers structDef(R"(struct <id> { <members> })");
+	unsigned numMembers = 0;
+	auto fieldGenerator = [&]() {
+		return Whiskers(R"(<typeName> <id>;)")
+			("typeName", typeName())
+			("id", "sm" + to_string(numMembers++))
+			.render();
 	};
+	structDef("members", generator(fieldGenerator, randOneToN(5), " ", true));
+	structDef("id", "s" + to_string(m_numStructs++));
+	m_out << structDef.render();
+	return antlrcpp::Any();
+}
 
-	string pragma = PickLiteral();
+antlrcpp::Any SolidityMutator::visitEnumDefinition(SolP::EnumDefinitionContext* _ctx)
+{
+	unsigned numEnums = 0;
+	string elements = generator(
+		[&]() { return "e" + to_string(numEnums++); },
+		randOneToN(5),
+		", ",
+		false
+	);
+	m_out << Whiskers(R"(enum <id> {<elements>})")
+		("id", "en" + to_string(m_numEnums++))
+		("elements", elements)
+		.render();
+	return antlrcpp::Any();
+}
 
-	m_out << Whiskers(s_pragmaDirective)("directive", pragma).render();
+string SolidityMutator::generator(function<string()> _gen, unsigned _n, string _separator, bool _removeDups)
+{
+	vector<string> g{};
+	generate_n(
+		back_inserter(g),
+		_n,
+		_gen
+	);
+	if (_removeDups)
+	{
+		sort(g.begin(), g.end());
+		g.erase(unique(g.begin(), g.end()), g.end());
+	}
+	return boost::algorithm::join(g, _separator);
+}
+
+string SolidityMutator::mutatePragma()
+{
+	string minVersion = generator(
+		[&]() { return genRandString(1, '0', '9'); },
+		3,
+		".",
+		false
+	);
+	string maxVersion = generator(
+		[&]() { return genRandString(1, '0', '9'); },
+		3,
+		".",
+		false
+	);
+	string lSign = coinToss() ? ">" : ">=";
+	string uSign = coinToss() ? "<" : "<=";
+	return Whiskers(R"(solidity <?l><lSign> <minV></l><?u> <uSign> <maxV></u>)")
+		("l", coinToss())
+		("u", coinToss())
+		("lSign", lSign)
+		("minV", minVersion)
+		("uSign", uSign)
+		("maxV", maxVersion)
+		.render();
+}
+
+void SolidityMutator::genContract()
+{
+	m_out << Whiskers(R"(contract <id> { function f0() public {} })")
+		("id", "C" + to_string(m_numContracts++))
+		.render();
+}
+
+antlrcpp::Any SolidityMutator::visitPragmaDirective(SolP::PragmaDirectiveContext* _ctx)
+{
+	fuzzRule(_ctx);
+	return antlrcpp::Any();
+}
+
+string SolidityMutator::genImport()
+{
+	string path = genRandomPath();
+	string id = genRandomId("Im");
+
+	Whiskers importPathAsId(R"(import <path> as <id>;)");
+	Whiskers importStarAsIdFromPath(R"(import * as <id> from <path>;)");
+	Whiskers importPath(R"(import <path>;)");
+
+	switch (randOneToN(4))
+	{
+	case 1:
+		return importPathAsId("path", path)("id", id).render();
+	case 2:
+		return importStarAsIdFromPath("id", id)("path", path).render();
+	case 3:
+	{
+		vector<string> symbols{};
+		unsigned numElements = randOneToN(10);
+		generate_n(
+			back_inserter(symbols),
+			numElements,
+			[&](){
+			  return Whiskers((R"(<?as><path> as <id><!as><symbol></as>)"))
+				  ("as", coinToss())
+				  ("path", genRandomPath())
+				  ("id", genRandomId("Im"))
+				  ("symbol", genRandString(5, 'A', 'z'))
+				  .render();
+			}
+		);
+		return Whiskers(R"(import {<syms>} from <path>;)")
+			("syms", boost::algorithm::join(symbols, ", "))
+			("path", path)
+			.render();
+	}
+	case 4:
+		return importPath("path", path).render();
+	}
+	assert(false);
+}
+
+antlrcpp::Any SolidityMutator::visitImportDirective(SolP::ImportDirectiveContext* _ctx)
+{
+	m_out << regex_replace(
+		_ctx->getText(),
+		regex("as|from|*|"),
+		" $& "
+	);
+	return antlrcpp::Any();
+}
+
+template<typename T>
+void SolidityMutator::interfaceContractLibraryVisitor(T* _ctx)
+{
+	assert(
+		antlrcpp::is<SolP::ContractDefinitionContext*>(_ctx) ||
+	    antlrcpp::is<SolP::InterfaceDefinitionContext*>(_ctx) ||
+        antlrcpp::is<SolP::LibraryDefinitionContext*>(_ctx)
+    );
+
+	string baseNames{};
+	bool atLeastOneBaseContract = m_numContracts > 0;
+	bool atLeastOneBaseInterface = m_numInterfaces > 0;
+	if (atLeastOneBaseContract || atLeastOneBaseInterface)
+		baseNames = generator(
+			[&]() {
+			  if (contractScope())
+			  {
+				  if (atLeastOneBaseContract && coinToss())
+					  return "C" + to_string(m_rand() % m_numContracts);
+				  else if (atLeastOneBaseInterface && coinToss())
+					  return "I" + to_string(m_rand() % m_numInterfaces);
+				  else
+					  return string{};
+			  }
+			  else if (interfaceScope() && atLeastOneBaseInterface)
+				  return "I" + to_string(m_rand() % m_numInterfaces);
+			  else
+				  return string{};
+			},
+			randOneToN(3),
+			", ",
+			true
+		);
+
+	string name{};
+	if (contractScope())
+		name = "C" + to_string(m_numContracts++);
+	else if (interfaceScope())
+		name = "I" + to_string(m_numInterfaces++);
+	else
+		name = "L" + to_string(m_numLibraries++);
+
+	Whiskers contractDef(R"(<?abs>abstract </abs><?c>contract</c><?i>interface</i><?l>library</l> <id><?inh> is <iid></inh> {)");
+
+	m_out << contractDef
+		("abs", absContractScope())
+		("c", contractScope())
+		("i", interfaceScope())
+		("l", libraryScope())
+		("id", name)
+		("inh", !libraryScope() && atLeastOneBaseContract && !baseNames.empty())
+		("iid", baseNames)
+		.render();
+	constructorDefined = false;
+	if (coinToss())
+		visitChildren(_ctx);
+	else
+	{
+		switch (randOneToN(10))
+		{
+		case 1:
+			if ((contractScope() || absContractScope()) && !constructorDefined)
+				m_out << "constructor() external {}";
+			break;
+		case 2:
+			if (!interfaceScope())
+				m_out << "function f() public {}";
+			else
+				m_out << "function f() external;";
+			break;
+		case 3:
+			genModifier();
+			break;
+		case 4:
+			if (contractScope() || absContractScope())
+				m_out << "fallback() external {}";
+			else if (interfaceScope())
+				m_out << "fallback() external;";
+			break;
+		case 5:
+			if (contractScope() || absContractScope())
+				m_out << "receive() external payable {}";
+			else if (interfaceScope())
+				m_out << "receive() external payable;";
+			break;
+		case 6:
+			m_out << "struct s { uint x; }";
+			break;
+		case 7:
+			m_out << "enum e { first }";
+			break;
+		case 8:
+			if (contractScope() || absContractScope())
+				m_out << "uint x;";
+			else if (libraryScope())
+				m_out << "uint constant x = 1337;";
+			break;
+		case 9:
+			m_out << "event e() anonymous;";
+			break;
+		case 10:
+			if (!interfaceScope())
+				m_out << "using L for *;";
+			break;
+		}
+	}
+
+	m_out << "}\n";
+}
+
+antlrcpp::Any SolidityMutator::visitContractDefinition(SolP::ContractDefinitionContext* _ctx)
+{
+	unsigned numGlobalFuncs = m_numFunctions;
+	m_numFunctions = 0;
+	ScopeGuard s( [&]() { m_type = Type::GLOBAL; m_numFunctions = numGlobalFuncs; });
+	m_type = _ctx->Abstract() ? Type::ABSCONTRACT : Type::CONTRACT;
+	interfaceContractLibraryVisitor(_ctx);
+	if (coinToss())
+		genContract();
+	return antlrcpp::Any();
+}
+
+antlrcpp::Any SolidityMutator::visitInterfaceDefinition(SolP::InterfaceDefinitionContext* _ctx)
+{
+	unsigned numGlobalFuncs = m_numFunctions;
+	m_numFunctions = 0;
+	ScopeGuard s( [&]() { m_type = Type::GLOBAL; m_numFunctions = numGlobalFuncs; });
+	m_type = Type::INTERFACE;
+	interfaceContractLibraryVisitor(_ctx);
+	return antlrcpp::Any();
+}
+
+antlrcpp::Any SolidityMutator::visitLibraryDefinition(SolP::LibraryDefinitionContext* _ctx)
+{
+	unsigned numGlobalFuncs = m_numFunctions;
+	m_numFunctions = 0;
+	ScopeGuard s( [&]() { m_type = Type::GLOBAL; m_numFunctions = numGlobalFuncs; });
+	m_type = Type::LIBRARY;
+	interfaceContractLibraryVisitor(_ctx);
+	return antlrcpp::Any();
+}
+
+template <typename T>
+void SolidityMutator::visitItemOrGenerate(T _item, function<void()> _generator)
+{
+	if (_item)
+		_item->accept(this);
+	else
+		_generator();
+}
+
+antlrcpp::Any SolidityMutator::visitContractBodyElement(SolP::ContractBodyElementContext* _ctx)
+{
+	return genericVisitor(_ctx, "contractbodyelement");
+}
+
+antlrcpp::Any SolidityMutator::visitTypeName(SolP::TypeNameContext*)
+{
+	m_out << typeName();
+	return antlrcpp::Any();
+}
+
+antlrcpp::Any SolidityMutator::visitParameterList(SolP::ParameterListContext* _ctx)
+{
+	vector<string> paramDecls{};
+	for (auto &i: _ctx->parameterDeclaration())
+		paramDecls.push_back(i->accept(this).as<string>());
+	generate_n(
+		back_inserter(paramDecls),
+		randOneToN(3),
+		[&]() {
+			return Whiskers(R"(<typeName> <dataLoc> <id>)")
+				("typeName", typeName())
+				("dataLoc", dataLocation())
+				("id", genRandomId("p", 10))
+				.render();
+		}
+    );
+	return boost::algorithm::join(paramDecls, ", ");
+}
+
+antlrcpp::Any SolidityMutator::visitParameterDeclaration(SolP::ParameterDeclarationContext* _ctx)
+{
+	Whiskers paramDecl(R"(<typeName> <dataLoc> <id>)");
+	return paramDecl("typeName", typeName())("dataLoc", dataLocation())("id", genRandomId("p", 10)).render();
+}
+
+antlrcpp::Any SolidityMutator::visitConstructorDefinition(SolP::ConstructorDefinitionContext* _ctx)
+{
+	// Skip over redundant constructor defs
+	if (!constructorDefined)
+	{
+		Whiskers constructorDef(R"(constructor (<args>) <payable> <visibility>)");
+		string args = _ctx->arguments ? _ctx->arguments->accept(this).as<string>() : "";
+		string visibility = coinToss() ? "public" : "internal";
+		string payable = coinToss() ? "payable" : "";
+		m_out << constructorDef("args", args)("payable", payable)("visibility", visibility).render();
+		constructorDefined = true;
+		if (_ctx->body)
+			_ctx->body->accept(this);
+		else
+			m_out << "{}";
+	}
+	return antlrcpp::Any();
+}
+
+antlrcpp::Any SolidityMutator::visitEventParameter(SolP::EventParameterContext* _ctx)
+{
+	return eventParam();
+}
+
+antlrcpp::Any SolidityMutator::visitEventDefinition(SolP::EventDefinitionContext* _ctx)
+{
+	Whiskers eventDef(R"(event <id>(<params>) <anonymous>;))");
+	eventDef("id", genRandomId("ev"));
+
+	vector<string> params{};
+	for (auto &i: _ctx->parameters)
+		params.push_back(i->accept(this).as<string>());
+	eventDef("params", boost::algorithm::join(params, ", "));
+	eventDef("anonymous", coinToss() ? "anonymous" : "");
+
+	m_out << eventDef.render();
+	vector<string> addEvents;
+	generate_n(
+		back_inserter(addEvents),
+		randOneToN(3),
+		[&]() {
+			Whiskers t = Whiskers(R"(event <id>(<params>) <anon>;)");
+			vector<string> params{};
+			generate_n(
+				back_inserter(params),
+				randOneToN(3),
+				[&]() { return eventParam(); }
+			);
+			return t
+				("id", genRandomId("p", 10))
+				("params", boost::algorithm::join(params, ", "))
+				("anon", coinToss() ? "anonymous" : "")
+				.render();
+		}
+	);
+	m_out << boost::algorithm::join(addEvents, "");
+	return antlrcpp::Any();
+}
+
+string SolidityMutator::genFunctionName()
+{
+	if (likely())
+		return "f" + to_string(m_numFunctions++);
+	else
+	{
+		if (coinToss())
+			return "fallback";
+		else
+			return "receive";
+	}
+}
+
+void SolidityMutator::genModifier()
+{
+	Whiskers modDef(R"(modifier <id> (<params>) <virtual> <override> <SemicolonOrBody>)");
+	modDef("id", "m" + to_string(m_numModifiers++));
+	modDef("params", "");
+	modDef("virtual", coinToss() ? "virtual" : "");
+	modDef("override", coinToss() ? "override": "");
+	modDef("SemicolonOrBody", coinToss() ? ";" : "{ _; }");
+	m_out << modDef.render();
+}
+
+antlrcpp::Any SolidityMutator::visitFunctionDefinition(SolP::FunctionDefinitionContext* _ctx)
+{
+	// Free functions cannot
+	// - have visibility
+	// - are not payable
+	// - are not virtual
+	// - cannot be overridden
+	string vis{};
+	if (interfaceScope())
+		vis = "external";
+	else if (contractScope() || libraryScope())
+		vis = visibility();
+	string mut = mutability();
+	if ((vis == "internal" || vis == "private") && mut == "payable")
+		vis = "public";
+	string id = genFunctionName();
+
+	// Must implement
+	bool mustImplement = contractScope() || libraryScope() || globalScope();
+	// May implement
+	bool mayImplement = absContractScope() && coinToss();
+
+	Whiskers functionDef(
+		R"(function <id>(<args>) <vis> <mut> <?virt>virtual</virt> <?oride>override</oride> <mod>)"
+	);
+	bool mayVirtualise = (contractScope() || absContractScope()) && (vis == "public" || vis == "external");
+	bool mayOverride = contractScope() || absContractScope() || interfaceScope();
+	m_out << functionDef
+		("id", id)
+		("args", _ctx->arguments ? _ctx->arguments->accept(this).as<string>() : "")
+		("vis", vis)
+		("mut", mut)
+		("virt", mayVirtualise && coinToss())
+		("oride", mayOverride && coinToss())
+		("mod", "")
+		.render();
+	if (_ctx->body && (mustImplement || mayImplement))
+		_ctx->body->accept(this);
+	else
+	{
+		if (mustImplement || mayImplement)
+			m_out << "{}";
+		else
+			m_out << ";";
+	}
+
+	return antlrcpp::Any();
+}
+
+antlrcpp::Any SolidityMutator::visitBlock(SolP::BlockContext* _ctx)
+{
+	m_out << "{}";
 	return antlrcpp::Any();
 }
\ No newline at end of file
diff --git a/test/tools/ossfuzz/SolidityMutator.h b/test/tools/ossfuzz/SolidityMutator.h
index 87cdaa58f..e09492449 100644
--- a/test/tools/ossfuzz/SolidityMutator.h
+++ b/test/tools/ossfuzz/SolidityMutator.h
@@ -31,9 +31,14 @@
 #include <random>
 
 namespace solidity::test::fuzzer {
+
 using RandomEngine = std::mt19937_64;
 using Dist = std::uniform_int_distribution<uint32_t>;
 
+struct Generator {
+	std::string operator()(std::string&& _template, std::map<std::string, std::string>&& _args);
+};
+
 class SolidityMutator: public SolidityBaseVisitor
 {
 public:
@@ -45,12 +50,201 @@ public:
 
 	antlrcpp::Any visitSourceUnit(SolidityParser::SourceUnitContext* _ctx) override;
 	antlrcpp::Any visitPragmaDirective(SolidityParser::PragmaDirectiveContext* _ctx) override;
+
+	antlrcpp::Any visitImportDirective(SolidityParser::ImportDirectiveContext* _ctx) override;
+	antlrcpp::Any visitContractDefinition(SolidityParser::ContractDefinitionContext* _ctx) override;
+	antlrcpp::Any visitContractBodyElement(SolidityParser::ContractBodyElementContext* _ctx) override;
+	antlrcpp::Any visitConstructorDefinition(SolidityParser::ConstructorDefinitionContext* _ctx) override;
+	antlrcpp::Any visitParameterList(SolidityParser::ParameterListContext* _ctx) override;
+	antlrcpp::Any visitParameterDeclaration(SolidityParser::ParameterDeclarationContext* _ctx) override;
+	antlrcpp::Any visitBlock(SolidityParser::BlockContext* _ctx) override;
+	antlrcpp::Any visitFunctionDefinition(SolidityParser::FunctionDefinitionContext* _ctx) override;
+	antlrcpp::Any visitEnumDefinition(SolidityParser::EnumDefinitionContext* _ctx) override;
+	antlrcpp::Any visitStructDefinition(SolidityParser::StructDefinitionContext* _ctx) override;
+	antlrcpp::Any visitEventDefinition(SolidityParser::EventDefinitionContext* _ctx) override;
+	antlrcpp::Any visitEventParameter(SolidityParser::EventParameterContext* _ctx) override;
+	antlrcpp::Any visitInterfaceDefinition(SolidityParser::InterfaceDefinitionContext* _ctx) override;
+	antlrcpp::Any visitLibraryDefinition(SolidityParser::LibraryDefinitionContext* _ctx) override;
+	antlrcpp::Any visitModifierDefinition(SolidityParser::ModifierDefinitionContext* _ctx) override;
+	/// Types
+	antlrcpp::Any visitTypeName(SolidityParser::TypeNameContext* _ctx) override;
+
 private:
+	enum class Type
+	{
+		CONTRACT,
+		ABSCONTRACT,
+		INTERFACE,
+		LIBRARY,
+		GLOBAL
+	};
+
+	bool globalScope()
+	{
+		return m_type == Type::GLOBAL;
+	}
+
+	bool absContractScope()
+	{
+		return m_type == Type::ABSCONTRACT;
+	}
+
+	bool contractScope()
+	{
+		return m_type == Type::CONTRACT;
+	}
+
+	bool libraryScope()
+	{
+		return m_type == Type::LIBRARY;
+	}
+
+	bool interfaceScope()
+	{
+		return m_type == Type::INTERFACE;
+	}
+
+	template <class C>
+	antlrcpp::Any genericVisitor(C* _ctx, std::string _ctxName);
+
+	template <typename T>
+	void interfaceContractLibraryVisitor(T* _ctx);
+
+	template <typename T>
+	void visitItemsOrGenerate(T _container, std::function<void()> _generator);
+
+	template <typename T>
+	void visitItemOrGenerate(T _item, std::function<void()> _generator);
+
+	bool likely()
+	{
+		return m_rand() % s_largePrime != 0;
+	}
+
 	/// @returns either true or false with roughly the same probability
 	bool coinToss()
 	{
 		return m_rand() % 2 == 0;
 	}
+
+	/// @returns a pseudo randomly chosen unsigned number between one
+	/// and @param _n
+	unsigned randOneToN(unsigned _n = 20)
+	{
+		return m_rand() % _n + 1;
+	}
+
+	/// @returns a pseudo randomly generated path string of
+	/// the form `<name>.sol` where `<name>` is a single
+	/// character in the ascii range [A-Z].
+	std::string genRandomPath()
+	{
+		return "\"" + genRandString(1, 'A', 'Z') + ".sol" + "\"";
+	}
+
+	/// @returns a pseudo randomly generated identifier that
+	/// comprises a single character in the ascii range [a-z].
+	std::string genRandomId(std::string _prefix, unsigned _n = 3)
+	{
+		return _prefix + std::to_string(m_rand() % _n);
+	}
+
+	template <typename T>
+	void genRule(T* _ctx);
+
+	template <typename T>
+	void mutateRule(T* _ctx);
+
+	void genContract();
+
+	void genModifier();
+
+	std::string generator(std::function<std::string()> _gen, unsigned _n, std::string _separator, bool _removeDups);
+
+	std::string genImport();
+
+	std::string genFunctionName();
+
+	/// @returns bit width as a string where bit width is a multiple
+	/// of 8 and in the range [8, 256].
+	std::string bitWidth()
+	{
+		return std::to_string(randOneToN(32) * 8);
+	}
+
+	/// @returns byte width as a string where byte width is in
+	/// the range [1, 32].
+	std::string byteWidth()
+	{
+		return std::to_string(randOneToN(32));
+	}
+
+	/// @returns a Solidity event parameter as string
+	std::string eventParam();
+
+	/// @returns a pseudo randomly chosen elementary Solidity type name
+	/// as a string including address payable type if @param _allowAddressPayable
+	/// is true (default), excluding otherwise.
+	std::string elementaryType(bool _allowAddressPayable = true);
+
+	/// @returns a pseudo randomly chosen Solidity type name as a string.
+	std::string typeName();
+
+	/// @returns a pseudo randomly chosen Solidity data location
+	std::string dataLocation();
+
+	/// @returns a pseudo randomly chosen Solidity function visibility.
+	std::string visibility();
+
+	/// @returns a pseudo randomly chosen Solidity function state mutability.
+	std::string mutability();
+
+	/// @returns a pseudo randomly generated user defined
+	/// type name that comprises at most @param _numIds identifiers separated
+	/// by a period ('.').
+	/// Each identifier is at most @param _len characters long each
+	/// character being choosen uniformly at random in the character
+	/// range between [@param _start, @param _end]
+	std::string genRandomUserDefinedTypeName(
+		unsigned _numIds = 2,
+		unsigned _len = 1,
+		char _start = 'a',
+		char _end = 'z'
+	);
+
+
+	/// @returns a pseudo randomly generated string of length at most
+	/// @param _maxLen characters where each character in the string
+	/// is in the ASCII character range between @param _start and
+	/// @param _end characters.
+	std::string genRandString(unsigned _maxLen, char _start = '!', char _end = '~');
+
+	/// Flag that indicates if contract constructor has been defined
+	bool constructorDefined = false;
+
+	unsigned m_numStructs = 0;
+	unsigned m_numFunctions = 0;
+	unsigned m_numLibraries = 0;
+	unsigned m_numContracts = 0;
+	unsigned m_numInterfaces = 0;
+	unsigned m_numEnums = 0;
+	unsigned m_numModifiers = 0;
+	Type m_type = Type::GLOBAL;
+
+	static constexpr unsigned s_maxPragmas = 2;
+	static constexpr unsigned s_maxImports = 2;
+
+	static constexpr unsigned s_largePrime = 1009;
+	void gen(SolidityParser::PragmaDirectiveContext*);
+	std::string mutatePragma();
+	template<typename T>
+	void fuzzRule(T* _ctx);
+	void mutate(SolidityParser::PragmaDirectiveContext*);
+	template<typename F, typename... Args>
+	auto mayRun(F&& _func, Args&&... _args, unsigned int _n = 101);
+	template<typename T, typename F, typename... Args>
+	void visitItemsOrGenerate(T _container, F&& _generator, Args&&... _args);
+
 	/// @returns a pseudo randomly chosen unsigned integer between one
 	/// and @param _n
 	uint32_t randomOneToN(uint32_t _n)
@@ -64,5 +258,6 @@ private:
 	RandomEngine m_rand;
 	/// Whisker template strings for Solidity syntax
 	const std::string s_pragmaDirective = R"(pragma <directive>;)";
+	void gen();
 };
 }
\ No newline at end of file