diff --git a/src/assembler.cpp b/src/assembler.cpp
new file mode 100644
index 0000000..c768811
--- /dev/null
+++ b/src/assembler.cpp
@@ -0,0 +1,330 @@
+#include "assembler.hpp"
+#include "builder.hpp"
+#include "scanner.hpp"
+#include "vm.hpp"
+#include <array>
+#include <cassert>
+#include <cstdint>
+#include <cstdlib>
+#include <expected>
+#include <format>
+#include <fstream>
+#include <ios>
+#include <memory>
+#include <string_view>
+#include <unordered_map>
+#include <vector>
+
+using namespace vc5::tools;
+using namespace vc5::tools::asmer;
+
+namespace fs = std::filesystem;
+
+using TT = Tok::Ty;
+
+auto vc5::tools::assemble_file(fs::path input_path, fs::path output_path)
+    -> std::expected<void, std::string>
+{
+    auto text = std::string();
+
+    {
+        auto input_file = std::ifstream(input_path, std::ios_base::binary);
+        if (not input_file) {
+            return std::unexpected(
+                std::format("could not open file '{}' for reading",
+                    std::string(input_path)));
+        }
+
+        input_file.seekg(0, std::ios_base::end);
+        auto size = input_file.tellg();
+        text.resize(static_cast<size_t>(size), '\0');
+        input_file.seekg(0);
+        input_file.read(&text[0], size);
+    }
+
+    auto parser = Parser(text);
+
+    auto program = std::vector<uint8_t>(65536);
+    auto builder = Builder(program.data());
+
+    auto assembler = Assembler(text, builder);
+
+    while (true) {
+        auto ins = parser.parse_ins();
+        if (not ins) {
+            break;
+        }
+    }
+
+    if (not parser.ok()) {
+        return std::unexpected("parsing failed");
+    }
+
+    {
+        auto output_file = std::ofstream(output_path, std::ios_base::binary);
+        if (not output_file) {
+            return std::unexpected(
+                std::format("could not open file '{}' for writing",
+                    std::string(input_path)));
+        }
+
+        output_file.write(reinterpret_cast<const char*>(program.data()),
+            static_cast<std::streamsize>(program.size()));
+    }
+
+    return {};
+}
+
+void Assembler::assemble_ins(Ins& ins)
+{
+    if (ins.labels) {
+        for (const auto& label : *ins.labels) {
+            if (label.is_local) {
+                m_local_labels[label.ident] = m_builder->ip();
+            } else {
+                m_local_labels.clear();
+                m_global_labels[label.ident] = m_builder->ip();
+            }
+        }
+    }
+
+    assemble_line(ins);
+}
+
+void Assembler::assemble_line(Ins& ins)
+{
+    if (ins.ident == "mov") {
+        if (arg_count_wrong(ins, 2))
+            return;
+    }
+
+    error(ins.loc,
+        std::format("instruction '{}' not supported/implemented", ins.ident));
+}
+
+bool Assembler::arg_count_wrong(Ins& ins, size_t count)
+{
+    if (ins.args.size() != count) {
+        error(ins.loc, std::format("expected {} operands", count));
+        return false;
+    }
+    return true;
+}
+
+void Assembler::error(Loc loc, std::string_view message)
+{
+    m_failed = true;
+    loc.print_error(m_text, message);
+}
+
+auto Parser::parse_ins() -> std::unique_ptr<Ins>
+{
+    auto loc = current_loc();
+
+    auto labels = Ins::Labels(nullptr);
+
+    auto ident = std::string_view();
+
+    while (true) {
+        while (eat('\n')) { }
+
+        if (test(TT::Ident) or eat('.')) {
+            bool is_local = false;
+            if (eat('.')) {
+                is_local = true;
+            }
+            if (not test(TT::Ident)) {
+                error(current_loc(), "expected ident");
+                return nullptr;
+            }
+            ident = m_tok.text;
+            step();
+
+            if (not eat(':')) {
+                if (not is_local) {
+                    break;
+                }
+
+                error(current_loc(), "expected ':'");
+                return nullptr;
+            }
+            if (not labels) {
+                labels = std::make_unique<std::vector<Label>>();
+            }
+            labels->push_back(Label { loc, ident, is_local });
+            continue;
+        } else {
+            return nullptr;
+        }
+    }
+
+    auto args = Ins::Args();
+
+    auto first = true;
+    while (not test(TT::Eof) and not eat('\n')) {
+        if (not first and not eat(',')) {
+            error(current_loc(), "expected ','");
+            return nullptr;
+        }
+        first = false;
+
+        auto arg = parse_expr();
+        if (not arg) {
+            return nullptr;
+        }
+        args.push_back(std::move(arg));
+    }
+
+    if (not test(TT::Eof) and not eat('\n')) {
+        error(current_loc(), "expected line ending");
+    }
+
+    return std::make_unique<Ins>(
+        loc, std::move(labels), ident, std::move(args));
+}
+
+auto Parser::parse_expr() -> std::unique_ptr<Expr>
+{
+    return parse_binary();
+}
+
+auto Parser::parse_binary(int prec) -> std::unique_ptr<Expr>
+{
+    using T = Expr::Ty;
+    using Op = std::tuple<TT, T, int>;
+
+    constexpr auto ops = std::array {
+        Op { TT::Pipe, T::Or, 4 },
+        Op { TT::Hat, T::Xor, 3 },
+        Op { TT::Ampersand, T::And, 2 },
+        Op { TT::Plus, T::Add, 1 },
+        Op { TT::Minus, T::Sub, 1 },
+    };
+
+    if (prec == 0) {
+        return parse_prefix();
+    }
+
+    auto loc = current_loc();
+
+    auto left = parse_binary(prec - 1);
+
+    auto should_continue = false;
+    while (should_continue) {
+        should_continue = false;
+        for (auto [op, ty, p] : ops) {
+            if (prec >= p and eat(op)) {
+                auto right = parse_binary(prec - 1);
+                left = std::make_unique<Expr>(loc,
+                    ty,
+                    Expr::Binary { std::move(left), std::move(right) });
+            }
+        }
+    }
+
+    return left;
+}
+
+auto Parser::parse_prefix() -> std::unique_ptr<Expr>
+{
+    auto loc = current_loc();
+    auto expr = parse_operand();
+    if (eat('-')) {
+        return std::make_unique<Expr>(loc, Expr::Ty::Negate, std::move(expr));
+    } else if (eat('!')) {
+        return std::make_unique<Expr>(loc, Expr::Ty::Not, std::move(expr));
+    } else {
+        return expr;
+    }
+}
+
+static const auto reg_idents = std::unordered_map<std::string_view, vc5::Reg> {
+    { "R0", vc5::Reg::R0 },
+    { "R1", vc5::Reg::R1 },
+    { "R2", vc5::Reg::R2 },
+    { "R3", vc5::Reg::R3 },
+    { "R4", vc5::Reg::R4 },
+    { "R5", vc5::Reg::R5 },
+    { "Rbp", vc5::Reg::Rbp },
+    { "Rsp", vc5::Reg::Rsp },
+    { "Rfl", vc5::Reg::Rfl },
+    { "Rip", vc5::Reg::Rip },
+};
+
+auto Parser::parse_operand() -> std::unique_ptr<Expr>
+{
+    auto loc = current_loc();
+    if (test(TT::Ident)) {
+        auto ident = m_tok.text;
+        step();
+        if (reg_idents.contains(ident)) {
+            return std::make_unique<Expr>(
+                loc, Expr::Ty::Reg, reg_idents.at(ident));
+        } else {
+            return std::make_unique<Expr>(loc, Expr::Ty::Ident, ident);
+        }
+    } else if (test(TT::Int)) {
+        auto text = std::string(m_tok.text);
+        auto value = std::strtol(text.c_str(), nullptr, 10);
+        return std::make_unique<Expr>(
+            loc, Expr::Ty::Int, static_cast<int>(value));
+    } else if (test(TT::Bin)) {
+        auto text = std::string(m_tok.text);
+        auto value = std::strtol(&text[2], nullptr, 2);
+        return std::make_unique<Expr>(
+            loc, Expr::Ty::Int, static_cast<int>(value));
+    } else if (test(TT::Hex)) {
+        auto text = std::string(m_tok.text);
+        auto value = std::strtol(&text[2], nullptr, 16);
+        return std::make_unique<Expr>(
+            loc, Expr::Ty::Int, static_cast<int>(value));
+    } else if (eat('(')) {
+        auto expr = parse_expr();
+        if (not eat(')')) {
+            error(current_loc(), "expected ')'");
+            return nullptr;
+        }
+        return expr;
+    } else if (eat('[')) {
+        auto expr = parse_expr();
+        if (not eat(']')) {
+            error(current_loc(), "expected ']'");
+            return nullptr;
+        }
+        return std::make_unique<Expr>(
+            loc, Expr::Ty::Indirection, std::move(expr));
+    } else {
+        error(current_loc(), "expected expression");
+        return nullptr;
+    }
+}
+
+auto Parser::eat(int ty) -> bool
+{
+    if (test(ty)) {
+        step();
+        return true;
+    }
+    return false;
+}
+
+void Parser::step()
+{
+    m_tok = m_lexer.next();
+}
+
+auto Parser::test(int ty) const -> bool
+{
+    return m_tok.ty == ty;
+}
+
+auto Parser::current_loc() const -> Loc
+{
+    return m_tok.loc;
+}
+
+void Parser::error(Loc loc, std::string_view message)
+{
+    m_error_occured = true;
+    loc.print_error(m_text, message);
+}
diff --git a/src/assembler.hpp b/src/assembler.hpp
new file mode 100644
index 0000000..27a520e
--- /dev/null
+++ b/src/assembler.hpp
@@ -0,0 +1,141 @@
+#pragma once
+
+#include "builder.hpp"
+#include "scanner.hpp"
+#include "vm.hpp"
+#include <cstdint>
+#include <expected>
+#include <filesystem>
+#include <memory>
+#include <string>
+#include <string_view>
+#include <unordered_map>
+#include <variant>
+#include <vector>
+
+namespace vc5::tools {
+
+namespace fs = std::filesystem;
+
+namespace asmer {
+
+    struct Label {
+        Loc loc;
+        std::string_view ident;
+        bool is_local;
+    };
+
+    struct Expr {
+        enum class Ty {
+            Ident,
+            Reg,
+            Int,
+            Indirection,
+            Negate,
+            Not,
+            Or,
+            Xor,
+            And,
+            Add,
+            Sub,
+        };
+
+        using Ptr = std::unique_ptr<Expr>;
+        using Binary = std::tuple<Ptr, Ptr>;
+        using Data = std::variant<std::string_view, Reg, int, Ptr, Binary>;
+
+        // clang-format off
+    auto as_ident() -> std::string_view& { return std::get<std::string_view>(data); }
+    auto as_reg() -> Reg& { return std::get<Reg>(data); }
+    auto as_int() -> int& { return std::get<int>(data); }
+    auto as_unary() -> Ptr& { return std::get<Ptr>(data); }
+    auto as_binary() -> Binary& { return std::get<Binary>(data); }
+        // clang-format on
+
+        Loc loc;
+        Ty ty;
+        Data data;
+    };
+
+    struct Ins {
+        using Labels = std::unique_ptr<std::vector<Label>>;
+        using Args = std::vector<std::unique_ptr<Expr>>;
+
+        Loc loc;
+        Labels labels;
+        std::string_view ident;
+        Args args;
+    };
+
+    class Parser {
+    public:
+        explicit Parser(std::string_view text)
+            : m_text(text)
+            , m_lexer(text)
+            , m_tok(m_lexer.next())
+        {
+        }
+
+        auto parse_ins() -> std::unique_ptr<Ins>;
+
+        auto ok() const -> bool
+        {
+            return m_lexer.ok() and not m_error_occured;
+        }
+
+    private:
+        auto parse_expr() -> std::unique_ptr<Expr>;
+        auto parse_binary(int prec = 20) -> std::unique_ptr<Expr>;
+        auto parse_prefix() -> std::unique_ptr<Expr>;
+        auto parse_operand() -> std::unique_ptr<Expr>;
+
+        auto eat(int ty) -> bool;
+        void step();
+
+        auto test(int ty) const -> bool;
+        auto current_loc() const -> Loc;
+
+        void error(Loc loc, std::string_view message);
+
+        std::string_view m_text;
+        Scanner m_lexer;
+        Tok m_tok;
+        bool m_error_occured = false;
+    };
+
+    class Assembler {
+    public:
+        explicit Assembler(std::string_view text, Builder& builder)
+            : m_text(text)
+            , m_builder(&builder)
+        {
+        }
+
+        void assemble_ins(Ins& ins);
+
+        auto ok() const -> bool
+        {
+            return not m_failed;
+        }
+
+    private:
+        void assemble_line(Ins& ins);
+
+        /// true means fail
+        bool arg_count_wrong(Ins& ins, size_t count);
+
+        void error(Loc loc, std::string_view message);
+
+        std::string_view m_text;
+        Builder* m_builder;
+        std::unordered_map<std::string_view, uint16_t> m_global_labels {};
+        std::unordered_map<std::string_view, uint16_t> m_local_labels {};
+        bool m_failed = false;
+    };
+
+}
+
+auto assemble_file(fs::path input_path, fs::path output_path)
+    -> std::expected<void, std::string>;
+
+}
diff --git a/src/block_device.hpp b/src/block_device.hpp
index 9809143..c925a1a 100644
--- a/src/block_device.hpp
+++ b/src/block_device.hpp
@@ -2,8 +2,10 @@
 
 #include <cstdint>
 #include <filesystem>
+#include <format>
 #include <fstream>
 #include <ios>
+#include <stdexcept>
 #include <vector>
 
 namespace vc5 {
@@ -53,6 +55,10 @@ public:
     explicit FileDisk(fs::path file_path)
         : m_file(file_path, std::ios_base::binary)
     {
+        if (not m_file) {
+            throw std::invalid_argument(std::format(
+                "unable to open file '{}'", std::string(file_path)));
+        }
     }
 
     auto block_count() -> uint16_t override;
diff --git a/src/builder.cpp b/src/builder.cpp
index 00d5f5a..c324ca8 100644
--- a/src/builder.cpp
+++ b/src/builder.cpp
@@ -4,7 +4,7 @@
 #include <print>
 #include <utility>
 
-using namespace vc5;
+using namespace vc5::tools;
 
 namespace {
 
diff --git a/src/builder.hpp b/src/builder.hpp
index 2ecc4be..0d2aa9b 100644
--- a/src/builder.hpp
+++ b/src/builder.hpp
@@ -4,7 +4,7 @@
 #include <cstdint>
 #include <print>
 
-namespace vc5 {
+namespace vc5::tools {
 
 using namespace vc5;
 
diff --git a/src/main.cpp b/src/main.cpp
index a4c1613..13abd9a 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -18,7 +18,7 @@ int main()
 
     auto disk = MemoryDisk(128);
 
-    auto l = Builder(disk.data());
+    auto l = tools::Builder(disk.data());
 
     l.mov_imm(rsp, 0x1000);
     l.mov_reg(rbp, rsp);
diff --git a/src/scanner.cpp b/src/scanner.cpp
new file mode 100644
index 0000000..6c67023
--- /dev/null
+++ b/src/scanner.cpp
@@ -0,0 +1,186 @@
+#include "scanner.hpp"
+#include <print>
+#include <string>
+#include <string_view>
+
+using namespace vc5::tools;
+using namespace std::literals;
+
+auto Scanner::next() -> Tok
+{
+    auto loc = this->current_loc();
+    if (done()) {
+        return tok(Tok::Eof, loc);
+    }
+    if (test_in(" \t\r")) {
+        while (test_in(" \t\r")) {
+            step();
+        }
+        return next();
+    }
+    if (test(';')) {
+        step();
+        while (not done() and not test('\n')) {
+            step();
+        }
+        return next();
+    }
+    if (test('_') or test_range('A', 'Z') or test_range('a', 'z')) {
+        while (test('_') or test_range('0', '9') or test_range('A', 'Z')
+            or test_range('a', 'z')) {
+            step();
+        }
+        return tok(Tok::Ident, loc);
+    }
+    if (test_range('1', '9')) {
+        while (test_range('0', '9')) {
+            step();
+        }
+        return tok(Tok::Int, loc);
+    }
+    if (test('0')) {
+        step();
+        if (test('b')) {
+            step();
+            while (test_in("01")) {
+                step();
+            }
+            return tok(Tok::Bin, loc);
+        } else if (test('x')) {
+            step();
+            while (test_range('0', '9') or test_range('a', 'f')
+                or test_range('A', 'F')) {
+                step();
+            }
+            return tok(Tok::Hex, loc);
+        } else {
+            return tok(Tok::Int, loc);
+        }
+    }
+    if (test_in("\n()[],:|^+-!")) {
+        auto ty = static_cast<Tok::Ty>(current());
+        step();
+        return tok(ty, loc);
+    }
+    error(loc, std::format("illegal character '{}'", current()));
+    step();
+    return next();
+}
+
+void Scanner::step()
+{
+    if (done())
+        return;
+
+    char ch = current();
+    m_idx += 1;
+
+    if (ch == '\n') {
+        m_line += 1;
+        m_col = 1;
+    } else {
+        m_col += 1;
+    }
+}
+
+auto Scanner::tok(Tok::Ty ty, Loc loc) const -> Tok
+{
+    return Tok { m_text.substr(loc.idx, m_idx - loc.idx), loc, ty };
+}
+
+auto Scanner::current_loc() const -> Loc
+{
+    return Loc { m_idx, m_line, m_col };
+}
+
+auto Scanner::test_range(char begin, char end) const -> bool
+{
+    return not done() and current() >= begin and current() <= end;
+}
+
+auto Scanner::test_in(std::string_view chars) const -> bool
+{
+    for (auto ch : chars) {
+        if (test(ch)) {
+            return true;
+        }
+    }
+    return false;
+}
+
+auto Scanner::test(char ch) const -> bool
+{
+    return not done() and current() == ch;
+}
+
+auto Scanner::current() const -> char
+{
+    return m_text[m_idx];
+}
+
+auto Scanner::done() const -> bool
+{
+    return m_idx >= m_text.size();
+}
+
+void Scanner::error(Loc loc, std::string_view message)
+{
+    m_error_occured = true;
+    loc.print_error(m_text, message);
+}
+
+void Loc::print_error(std::string_view text, std::string_view message) const
+{
+    constexpr auto type = "error"sv;
+
+    constexpr auto clear = "\x1b[0m"sv;
+    constexpr auto bold_red = "\x1b[1;31m"sv;
+    constexpr auto bold_white = "\x1b[1;37m"sv;
+    constexpr auto cyan = "\x1b[0;36m"sv;
+    constexpr auto gray = "\x1b[0;37m"sv;
+    constexpr auto light_gray = "\x1b[1;30m"sv;
+
+    auto start = text.find_last_of('\n', idx) + 1;
+    auto end = text.find_first_of('\n', idx);
+
+    if (end == std::string_view::npos) {
+        end = text.size();
+    }
+
+    auto line_text = text.substr(start, end - start);
+
+    auto linenr_str = std::to_string(line);
+
+    std::println(""
+                 "{0}{1}{2}: {3}\n"
+                 " {4}--> {5}:{6}:{7}\n"
+                 " {8: <{9}}{10}|\n"
+                 " {11}{12}{13}|{14}{15}\n"
+                 " {16: <{17}}"
+                 "{18}|${19: <{20}}{21}^ {22}{23}{24}",
+        bold_red,
+        type,
+        bold_white,
+        message,
+        cyan,
+        "<file>",
+        line,
+        col,
+        "",
+        linenr_str.size(),
+        gray,
+        light_gray,
+        linenr_str,
+        gray,
+        light_gray,
+        line_text,
+        "",
+        linenr_str.size(),
+        gray,
+        "",
+        col - 1,
+        bold_red,
+        bold_white,
+        message,
+        clear);
+}
diff --git a/src/scanner.hpp b/src/scanner.hpp
new file mode 100644
index 0000000..7213eb8
--- /dev/null
+++ b/src/scanner.hpp
@@ -0,0 +1,77 @@
+#pragma once
+
+#include <cstddef>
+#include <string_view>
+
+namespace vc5::tools {
+
+struct Loc {
+    size_t idx;
+    int line;
+    int col;
+
+    void print_error(std::string_view text, std::string_view message) const;
+};
+
+struct Tok {
+    enum Ty {
+        Eof,
+        Ident,
+        Int,
+        Hex,
+        Bin,
+        Newline = '\n',
+        LParen = '(',
+        RParen = ')',
+        LBracket = '[',
+        RBracket = ']',
+        Comma = ',',
+        Colon = ':',
+        Pipe = '|',
+        Hat = '^',
+        Ampersand = '&',
+        Plus = '+',
+        Minus = '-',
+        Exclam = '!',
+    };
+
+    std::string_view text;
+    Loc loc;
+    Ty ty;
+};
+
+class Scanner {
+public:
+    explicit Scanner(std::string_view text)
+        : m_text(text)
+    {
+    }
+
+    auto next() -> Tok;
+
+    auto ok() const -> bool
+    {
+        return not m_error_occured;
+    }
+
+private:
+    void step();
+
+    auto tok(Tok::Ty ty, Loc loc) const -> Tok;
+    auto current_loc() const -> Loc;
+    auto test_range(char begin, char end) const -> bool;
+    auto test_in(std::string_view chars) const -> bool;
+    auto test(char ch) const -> bool;
+    auto current() const -> char;
+    auto done() const -> bool;
+
+    void error(Loc loc, std::string_view message);
+
+    std::string_view m_text;
+    size_t m_idx = 0;
+    int m_line = 1;
+    int m_col = 1;
+    bool m_error_occured = false;
+};
+
+}