diff --git a/core/src/Schematic.cpp b/core/src/Schematic.cpp
new file mode 100644
index 0000000..e26e8b2
--- /dev/null
+++ b/core/src/Schematic.cpp
@@ -0,0 +1,160 @@
+#include "vf/Schematic.h"
+
+#include <algorithm>
+
+namespace vf {
+
+namespace {
+
+constexpr uint32_t schematicMagic = 0x56585343u;   // "VXSC"
+constexpr std::size_t maxSchematicCells = 1u << 26;
+constexpr uint8_t voidMaskFlag = 0x01;
+
+std::size_t packedByteCount(std::size_t cells, uint8_t bits) {
+    return (cells * static_cast<std::size_t>(bits) + 7u) / 8u;
+}
+
+// Indices are packed low bits first. Every supported width divides eight, so a
+// value never straddles two bytes and the reader can address it directly.
+void packIndices(const std::vector<uint16_t>& indices, uint8_t bits, ByteBuffer& out) {
+    std::size_t base = out.size();
+    out.resize(base + packedByteCount(indices.size(), bits));
+    uint32_t mask = (1u << bits) - 1u;
+    for (std::size_t i = 0; i < indices.size(); ++i) {
+        std::size_t bitPosition = i * bits;
+        std::size_t byteIndex = base + (bitPosition >> 3);
+        unsigned shift = static_cast<unsigned>(bitPosition & 7u);
+        out[byteIndex] |= static_cast<uint8_t>((indices[i] & mask) << shift);
+    }
+}
+
+void unpackIndices(const uint8_t* data, std::size_t cells, uint8_t bits,
+                   std::vector<uint16_t>& out) {
+    out.assign(cells, 0u);
+    uint32_t mask = (1u << bits) - 1u;
+    for (std::size_t i = 0; i < cells; ++i) {
+        std::size_t bitPosition = i * bits;
+        unsigned shift = static_cast<unsigned>(bitPosition & 7u);
+        out[i] = static_cast<uint16_t>((data[bitPosition >> 3] >> shift) & mask);
+    }
+}
+
+void buildPalette(const ClipboardBuffer& buffer, std::vector<Block>& palette,
+                  std::vector<uint16_t>& slotOfBlock) {
+    palette.clear();
+    slotOfBlock.assign(static_cast<std::size_t>(Block::Count), 0u);
+    std::vector<uint8_t> used(static_cast<std::size_t>(Block::Count), 0u);
+    used[static_cast<std::size_t>(Block::Air)] = 1u;
+
+    const Vec3i& dims = buffer.dims();
+    for (int y = 0; y < dims.y; ++y)
+        for (int z = 0; z < dims.z; ++z)
+            for (int x = 0; x < dims.x; ++x) {
+                if (!buffer.filledAt(x, y, z)) continue;
+                used[static_cast<std::size_t>(buffer.at(x, y, z))] = 1u;
+            }
+
+    palette.push_back(Block::Air);
+    for (std::size_t id = 0; id < used.size(); ++id) {
+        if (used[id] == 0u || static_cast<Block>(id) == Block::Air) continue;
+        slotOfBlock[id] = static_cast<uint16_t>(palette.size());
+        palette.push_back(static_cast<Block>(id));
+    }
+}
+
+void putI32(ByteWriter& writer, int value) { writer.putU32(static_cast<uint32_t>(value)); }
+
+bool getI32(ByteReader& reader, int& out) {
+    uint32_t raw = 0;
+    if (!reader.getU32(raw)) return false;
+    out = static_cast<int>(static_cast<int32_t>(raw));
+    return true;
+}
+
+} // namespace
+
+ClipboardBuffer::ClipboardBuffer(const Vec3i& dims, const Vec3i& anchor) {
+    if (dims.x <= 0 || dims.y <= 0 || dims.z <= 0) return;
+    size = dims;
+    handle = anchor;
+    blocks.assign(volume(), Block::Air);
+    present = SelectionMask(Vec3i{0, 0, 0}, dims);
+}
+
+std::size_t ClipboardBuffer::volume() const {
+    return static_cast<std::size_t>(size.x) * static_cast<std::size_t>(size.y) *
+           static_cast<std::size_t>(size.z);
+}
+
+bool ClipboardBuffer::inBounds(int x, int y, int z) const {
+    return x >= 0 && x < size.x && y >= 0 && y < size.y && z >= 0 && z < size.z;
+}
+
+std::size_t ClipboardBuffer::indexOf(int x, int y, int z) const {
+    return (static_cast<std::size_t>(y) * static_cast<std::size_t>(size.z) +
+            static_cast<std::size_t>(z)) *
+               static_cast<std::size_t>(size.x) +
+           static_cast<std::size_t>(x);
+}
+
+Block ClipboardBuffer::at(int x, int y, int z) const {
+    if (!inBounds(x, y, z)) return Block::Air;
+    return blocks[indexOf(x, y, z)];
+}
+
+bool ClipboardBuffer::filledAt(int x, int y, int z) const {
+    if (!inBounds(x, y, z)) return false;
+    return present.contains(Vec3i{x, y, z});
+}
+
+void ClipboardBuffer::put(int x, int y, int z, Block block, bool filled) {
+    if (!inBounds(x, y, z)) return;
+    blocks[indexOf(x, y, z)] = block;
+    present.setCell(Vec3i{x, y, z}, filled);
+}
+
+void ClipboardBuffer::clearCell(int x, int y, int z) {
+    if (!inBounds(x, y, z)) return;
+    blocks[indexOf(x, y, z)] = Block::Air;
+    present.remove(Vec3i{x, y, z});
+}
+
+ClipboardBuffer ClipboardBuffer::copyFromWorld(const World& world, const Selection& selection) {
+    if (selection.empty()) return ClipboardBuffer{};
+    Vec3i origin = selection.min();
+    ClipboardBuffer copy(selection.dims(), Vec3i{0, 0, 0});
+    selection.forEach([&](const Vec3i& cell) {
+        copy.put(cell.x - origin.x, cell.y - origin.y, cell.z - origin.z,
+                 world.blockAt(cell.x, cell.y, cell.z), true);
+    });
+    return copy;
+}
+
+ClipboardBuffer ClipboardBuffer::rotatedY(Rotation rotation) const {
+    if (rotation == Rotation::None || empty()) return *this;
+
+    bool swapsAxes = rotation == Rotation::Cw90 || rotation == Rotation::Cw270;
+    Vec3i newDims = swapsAxes ? Vec3i{size.z, size.y, size.x} : size;
+
+    auto mapCell = [&](int x, int y, int z, int& outX, int& outY, int& outZ) {
+        outY = y;
+        switch (rotation) {
+            case Rotation::Cw90:
+                outX = size.z - 1 - z;
+                outZ = x;
+                break;
+            case Rotation::Cw180:
+                outX = size.x - 1 - x;
+                outZ = size.z - 1 - z;
+                break;
+            case Rotation::Cw270:
+                outX = z;
+                outZ = size.x - 1 - x;
+                break;
+            case Rotation::None:
+                outX = x;
+                outZ = z;
+                break;
+        }
+    };
+