diff --git a/core/src/DataPack.cpp b/core/src/DataPack.cpp
index 25bf783..9c3cf91 100644
--- a/core/src/DataPack.cpp
+++ b/core/src/DataPack.cpp
@@ -316,3 +316,161 @@ void TagRegistry::clear() { tags.clear(); }
 
 bool TagRegistry::has(const ResourceId& id) const { return tags.count(id) > 0u; }
 
+const BlockTag* TagRegistry::find(const ResourceId& id) const {
+    auto found = tags.find(id);
+    return found == tags.end() ? nullptr : &found->second;
+}
+
+std::vector<ResourceId> TagRegistry::ids() const {
+    std::vector<ResourceId> out;
+    out.reserve(tags.size());
+    for (const auto& entry : tags) out.push_back(entry.first);
+    return out;
+}
+
+namespace {
+
+bool expandTag(const TagRegistry& registry, const ResourceId& id, std::vector<ResourceId>& out,
+               std::vector<ResourceId>& path, std::vector<ResourceId>& expanded,
+               std::string& problem) {
+    for (const ResourceId& onPath : path) {
+        if (onPath == id) {
+            problem = "tag cycle through " + id.text();
+            return false;
+        }
+    }
+    for (const ResourceId& done : expanded)
+        if (done == id) return true;
+
+    const BlockTag* tag = registry.find(id);
+    if (tag == nullptr) {
+        problem = "unknown tag " + id.text();
+        return false;
+    }
+    path.push_back(id);
+    for (const BlockTag::Entry& entry : tag->entries) {
+        if (entry.reference) {
+            if (!expandTag(registry, entry.id, out, path, expanded, problem)) return false;
+            continue;
+        }
+        bool already = false;
+        for (const ResourceId& present : out)
+            if (present == entry.id) already = true;
+        if (!already) out.push_back(entry.id);
+    }
+    path.pop_back();
+    expanded.push_back(id);
+    return true;
+}
+
+} // namespace
+
+bool TagRegistry::resolve(const ResourceId& id, std::vector<ResourceId>& out,
+                          std::string& problem) const {
+    out.clear();
+    std::vector<ResourceId> path;
+    std::vector<ResourceId> expanded;
+    if (!expandTag(*this, id, out, path, expanded, problem)) {
+        out.clear();
+        return false;
+    }
+    return true;
+}
+
+bool TagRegistry::resolve(const ResourceId& id, std::vector<ResourceId>& out) const {
+    std::string ignored;
+    return resolve(id, out, ignored);
+}
+
+bool TagRegistry::contains(const ResourceId& id, const ResourceId& member) const {
+    std::vector<ResourceId> members;
+    if (!resolve(id, members)) return false;
+    for (const ResourceId& present : members)
+        if (present == member) return true;
+    return false;
+}
+
+bool TagRegistry::hasCycle(const ResourceId& id) const {
+    std::vector<ResourceId> members;
+    std::string problem;
+    if (resolve(id, members, problem)) return false;
+    return problem.compare(0, 10, "tag cycle ") == 0;
+}
+
+bool parseRecipeJson(const JsonValue& root, const std::string& defaultSpace, RecipeData& out,
+                     std::string& problem) {
+    if (!root.isObject()) {
+        problem = "a recipe must be an object";
+        return false;
+    }
+    const JsonValue* type = root.find("type");
+    if (type == nullptr || !type->isString()) {
+        problem = "\"type\" must be one of craftingShaped, craftingShapeless, smelting";
+        return false;
+    }
+    const JsonValue* result = root.find("result");
+    if (result == nullptr || !result->isObject()) {
+        problem = "\"result\" must be an object";
+        return false;
+    }
+    RecipeData parsed;
+    if (!readItemField(*result, "item", defaultSpace, parsed.resultItem, problem)) return false;
+    parsed.resultCount = static_cast<int>(result->intOr("count", 1));
+    if (parsed.resultCount < 1 || parsed.resultCount > maxStackSize(parsed.resultItem)) {
+        problem = "result count out of range for " + result->stringOr("item", "");
+        return false;
+    }
+
+    const std::string& kindName = type->stringValue();
+    if (kindName == "craftingShaped") {
+        parsed.kind = RecipeData::Kind::Shaped;
+        const JsonValue* pattern = root.find("pattern");
+        const JsonValue* key = root.find("key");
+        if (pattern == nullptr || !pattern->isArray() || pattern->elements().empty()) {
+            problem = "\"pattern\" must be a non empty array of rows";
+            return false;
+        }
+        if (key == nullptr || !key->isObject()) {
+            problem = "\"key\" must be an object mapping pattern characters to items";
+            return false;
+        }
+        if (pattern->elements().size() > static_cast<std::size_t>(craftGridHeight)) {
+            problem = "\"pattern\" is taller than the crafting grid";
+            return false;
+        }
+        parsed.height = static_cast<int>(pattern->elements().size());
+        parsed.width = -1;
+        parsed.pattern.fill(ItemId::None);
+        for (int row = 0; row < parsed.height; ++row) {
+            const JsonValue& line = pattern->elements()[static_cast<std::size_t>(row)];
+            if (!line.isString()) {
+                problem = "\"pattern\" rows must be strings";
+                return false;
+            }
+            const std::string& cells = line.stringValue();
+            if (cells.empty() || cells.size() > static_cast<std::size_t>(craftGridWidth)) {
+                problem = "\"pattern\" row width must be 1 to 3 characters";
+                return false;
+            }
+            if (parsed.width < 0) parsed.width = static_cast<int>(cells.size());
+            if (parsed.width != static_cast<int>(cells.size())) {
+                problem = "\"pattern\" rows are not all the same width";
+                return false;
+            }
+            for (int column = 0; column < parsed.width; ++column) {
+                char symbol = cells[static_cast<std::size_t>(column)];
+                if (symbol == ' ') continue;
+                ItemId ingredient = ItemId::None;
+                if (!readItemField(*key, std::string(1, symbol), defaultSpace, ingredient,
+                                   problem)) {
+                    problem = "pattern character '" + std::string(1, symbol) + "': " + problem;
+                    return false;
+                }
+                // Packed by the recipe's own width, which is how matchesShaped
+                // in Crafting.cpp indexes a pattern.
+                parsed.pattern[static_cast<std::size_t>(row * parsed.width + column)] = ingredient;
+            }
+        }
+        parsed.allowMirror = root.boolOr("mirror", true);
+    } else if (kindName == "craftingShapeless") {
+        parsed.kind = RecipeData::Kind::Shapeless;