diff --git a/Emulator/src/main/java/com/eu/habbo/habbohotel/items/FurnidataWriter.java b/Emulator/src/main/java/com/eu/habbo/habbohotel/items/FurnidataWriter.java
new file mode 100644
index 00000000..e525a14e
--- /dev/null
+++ b/Emulator/src/main/java/com/eu/habbo/habbohotel/items/FurnidataWriter.java
@@ -0,0 +1,197 @@
+package com.eu.habbo.habbohotel.items;
+
+import java.io.IOException;
+import java.nio.charset.StandardCharsets;
+import java.nio.file.*;
+import java.util.Comparator;
+import java.util.List;
+import java.util.regex.Matcher;
+import java.util.regex.Pattern;
+
+/**
+ * Comment-preserving, atomic, backed-up writer for furnidata name/description, keyed by
+ * classname. Supports single-file and split-tier (writes the tier that currently resolves
+ * the classname). Edit-only: refuses classnames absent from the furnidata.
+ */
+public class FurnidataWriter {
+    private final Path source;        // file (single) or base dir (split-tier)
+    private final boolean directory;  // true => split-tier
+    private final long maxBytes;
+    private final int backupKeep;
+
+    public FurnidataWriter(Path source, boolean directory, long maxBytes, int backupKeep) {
+        this.source = source;
+        this.directory = directory;
+        this.maxBytes = maxBytes;
+        this.backupKeep = Math.max(1, backupKeep);
+    }
+
+    /** @return true if an entry for classname was found and written. */
+    public boolean write(String classname, String name, String description) throws IOException {
+        String cn = classname == null ? "" : classname.trim().toLowerCase(java.util.Locale.ROOT);
+        if (cn.isEmpty()) return false;
+        String safeName = FurnitureTextProvider.sanitize(name);
+        String safeDesc = FurnitureTextProvider.sanitize(description);
+
+        Path target = locateFile(cn);
+        if (target == null) return false;
+
+        String raw = Files.readString(target, StandardCharsets.UTF_8);
+        String edited = replaceEntryFields(raw, cn, safeName, safeDesc);
+        if (edited == null || edited.equals(raw)) {
+            // classname not present in this file, or no change
+            return edited != null && !edited.equals(raw);
+        }
+        backup(target);
+        atomicWrite(target, edited);
+        return true;
+    }
+
+    /** For single-file just returns the file; for split-tier, the tier file that contains cn. */
+    private Path locateFile(String cn) throws IOException {
+        if (!directory) {
+            // confirm existence via the reader (size-guarded, parses the same way)
+            return containsClassname(source, cn) ? source : null;
+        }
+        // split-tier: iterate tiers in OVERRIDE order (later tiers win); pick the last containing cn
+        Path winner = null;
+        for (Path tierFile : splitTierFilesInOrder()) {
+            if (containsClassname(tierFile, cn)) winner = tierFile;
+        }
+        return winner;
+    }
+
+    private boolean containsClassname(Path file, String cn) {
+        for (FurnidataEntry e : new FurnidataReader(file, maxBytes).read()) {
+            if (e.classname() != null && e.classname().trim().toLowerCase(java.util.Locale.ROOT).equals(cn)) return true;
+        }
+        return false;
+    }
+
+    /**
+     * Replace the "name" and "description" string values inside the JSON object that holds
+     * "classname": "<cn>". Preserves everything else (comments, ordering, formatting).
+     * Handles double- and single-quoted JSON5 keys/values. Returns null if cn not found.
+     */
+    static String replaceEntryFields(String raw, String cn, String name, String description) {
+        // find the classname value occurrence (case-insensitive on the value)
+        Pattern classProp = Pattern.compile(
+            "([\"'])classname\\1\\s*:\\s*([\"'])((?:\\\\.|(?!\\2).)*)\\2", Pattern.CASE_INSENSITIVE);
+        Matcher m = classProp.matcher(raw);
+        int objStart = -1, objEnd = -1;
+        while (m.find()) {
+            String val = m.group(3).trim().toLowerCase(java.util.Locale.ROOT);
+            if (!val.equals(cn)) continue;
+            // expand to the enclosing { ... }
+            objStart = lastUnbalancedBrace(raw, m.start());
+            objEnd = matchingClose(raw, objStart);
+            break;
+        }
+        if (objStart < 0 || objEnd < 0) return null;
+        String obj = raw.substring(objStart, objEnd + 1);
+        String newObj = replaceField(obj, "name", name);
+        newObj = replaceField(newObj, "description", description);
+        return raw.substring(0, objStart) + newObj + raw.substring(objEnd + 1);
+    }
+
+    private static String replaceField(String obj, String field, String value) {
+        Pattern p = Pattern.compile(
+            "(([\"'])" + Pattern.quote(field) + "\\2\\s*:\\s*)([\"'])((?:\\\\.|(?!\\3).)*)\\3");
+        Matcher m = p.matcher(obj);
+        if (!m.find()) return obj; // field absent → leave object as-is
+        String replacement = m.group(1) + '"' + jsonEscape(value) + '"';
+        return obj.substring(0, m.start()) + replacement + obj.substring(m.end());
+    }
+
+    private static int lastUnbalancedBrace(String s, int from) {
+        int depth = 0;
+        for (int i = from; i >= 0; i--) {
+            char c = s.charAt(i);
+            if (c == '}') depth++;
+            else if (c == '{') { if (depth == 0) return i; depth--; }
+        }
+        return -1;
+    }
+
+    private static int matchingClose(String s, int open) {
+        int depth = 0; boolean inStr = false; char q = 0;
+        for (int i = open; i < s.length(); i++) {
+            char c = s.charAt(i);
+            if (inStr) { if (c == '\\') { i++; } else if (c == q) inStr = false; continue; }
+            if (c == '"' || c == '\'') { inStr = true; q = c; }
+            else if (c == '{') depth++;
+            else if (c == '}') { depth--; if (depth == 0) return i; }
+        }
+        return -1;
+    }
+
+    private static String jsonEscape(String v) {
+        StringBuilder b = new StringBuilder(v.length() + 8);
+        for (int i = 0; i < v.length(); i++) {
+            char c = v.charAt(i);
+            if (c == '"' || c == '\\') b.append('\\').append(c);
+            else b.append(c);
+        }
+        return b.toString();
+    }
+
+    private List<Path> splitTierFilesInOrder() throws IOException {
+        // Mirrors FurnidataReader split-tier resolution at a coarse level: the manifest order.
+        // For the plan we reuse the reader's defaults; the concrete enumeration is implemented
+        // in Task 4 alongside the split-tier test. Single-file path does not call this.
+        throw new UnsupportedOperationException("implemented in Task 4");
+    }
+
+    private void backup(Path target) throws IOException {
+        Path bak = target.resolveSibling(target.getFileName() + ".bak." + System.nanoTime());
+        Files.copy(target, bak, StandardCopyOption.COPY_ATTRIBUTES);
+        pruneBackups(target);
+    }
+
+    private void pruneBackups(Path target) throws IOException {
+        String prefix = target.getFileName() + ".bak.";
+        try (var stream = Files.list(target.getParent())) {
+            List<Path> baks = stream.filter(p -> p.getFileName().toString().startsWith(prefix))
+                .sorted(Comparator.comparingLong(p -> backupStamp(p))).toList();
+            for (int i = 0; i < baks.size() - backupKeep; i++) Files.deleteIfExists(baks.get(i));
+        }
+    }
+
+    private static long backupStamp(Path p) {
+        String s = p.getFileName().toString();
+        try { return Long.parseLong(s.substring(s.lastIndexOf('.') + 1)); } catch (Exception e) { return 0L; }
+    }
+
+    private void atomicWrite(Path target, String content) throws IOException {
+        Path tmp = target.resolveSibling(target.getFileName() + ".tmp." + System.nanoTime());
+        Files.writeString(tmp, content, StandardCharsets.UTF_8);
+        try {
+            Files.move(tmp, target, StandardCopyOption.REPLACE_EXISTING, StandardCopyOption.ATOMIC_MOVE);
+        } catch (AtomicMoveNotSupportedException e) {
+            Files.move(tmp, target, StandardCopyOption.REPLACE_EXISTING);
+        }
+    }
+
+    /** Restore the most recent backup of the (single-file) target. @return true if restored. */
+    public boolean revertLastBackup() throws IOException {
+        if (directory) return revertSplitTier();
+        return revertFile(source);
+    }
+
+    private boolean revertFile(Path target) throws IOException {
+        String prefix = target.getFileName() + ".bak.";
+        try (var stream = Files.list(target.getParent())) {
+            Path latest = stream.filter(p -> p.getFileName().toString().startsWith(prefix))
+                .max(Comparator.comparingLong(FurnidataWriter::backupStamp)).orElse(null);
+            if (latest == null) return false;
+            atomicWrite(target, Files.readString(latest, StandardCharsets.UTF_8));
+            return true;
+        }
+    }
+
+    private boolean revertSplitTier() throws IOException {
+        boolean any = false;
+        for (Path f : splitTierFilesInOrder()) any |= revertFile(f);
+        return any;
+    }
+}
diff --git a/Emulator/src/test/java/com/eu/habbo/habbohotel/items/FurnidataWriterTest.java b/Emulator/src/test/java/com/eu/habbo/habbohotel/items/FurnidataWriterTest.java
new file mode 100644
index 00000000..16faeb76
--- /dev/null
+++ b/Emulator/src/test/java/com/eu/habbo/habbohotel/items/FurnidataWriterTest.java
@@ -0,0 +1,40 @@
+package com.eu.habbo.habbohotel.items;
+
+import org.junit.jupiter.api.Test;
+import java.nio.file.*;
+import static org.junit.jupiter.api.Assertions.*;
+
+class FurnidataWriterTest {
+
+    private static final String SINGLE =
+        "{ \"roomitemtypes\": { \"furnitype\": [\n" +
+        "  { \"id\": 1, \"classname\": \"01_caterhead\", \"name\": \"old name\", \"description\": \"old desc\" }\n" +
+        "] }, \"wallitemtypes\": { \"furnitype\": [] } }";
+
+    @Test
+    void writesNameAndDescriptionByClassnameSingleFile() throws Exception {
+        Path dir = Files.createTempDirectory("fd");
+        Path file = dir.resolve("FurnitureData.json");
+        Files.writeString(file, SINGLE);
+
+        FurnidataWriter w = new FurnidataWriter(file, false, 64L * 1024 * 1024, 10);
+        boolean ok = w.write("01_caterhead", "Cat Head", "A cat head");
+
+        assertTrue(ok);
+        String after = Files.readString(file);
+        assertTrue(after.contains("\"Cat Head\""));
+        assertTrue(after.contains("\"A cat head\""));
+        assertFalse(after.contains("old name"));
+        // backup created
+        assertTrue(Files.list(dir).anyMatch(p -> p.getFileName().toString().startsWith("FurnitureData.json.bak")));
+    }
+
+    @Test
+    void rejectsUnknownClassname() throws Exception {
+        Path dir = Files.createTempDirectory("fd");
+        Path file = dir.resolve("FurnitureData.json");
+        Files.writeString(file, SINGLE);
+        FurnidataWriter w = new FurnidataWriter(file, false, 64L * 1024 * 1024, 10);
+        assertFalse(w.write("does_not_exist", "x", "y"));
+    }
+}