diff --git a/cache/src/main/kotlin/org/openrs2/cache/FlatFileStoreZipWriter.kt b/cache/src/main/kotlin/org/openrs2/cache/FlatFileStoreZipWriter.kt
new file mode 100644
index 00000000..3a1b6125
--- /dev/null
+++ b/cache/src/main/kotlin/org/openrs2/cache/FlatFileStoreZipWriter.kt
@@ -0,0 +1,91 @@
+package org.openrs2.cache
+
+import io.netty.buffer.ByteBuf
+import java.nio.file.attribute.FileTime
+import java.time.Instant
+import java.util.zip.Deflater
+import java.util.zip.ZipEntry
+import java.util.zip.ZipOutputStream
+
+/**
+ * A specialised [Store] implementation that writes a cache in the
+ * [FlatFileStore] format to a [ZipOutputStream].
+ *
+ * The cache is not buffered to disk.
+ *
+ * This implementation only supports the [create] and [write] methods. All
+ * other methods throw [UnsupportedOperationException].
+ *
+ * It is only intended for use by the cache archiving service's web interface.
+ */
+public class FlatFileStoreZipWriter(
+    private val out: ZipOutputStream,
+    private val prefix: String = "cache/",
+    level: Int = Deflater.BEST_COMPRESSION,
+    timestamp: Instant = Instant.EPOCH
+) : Store {
+    private val timestamp = FileTime.from(timestamp)
+
+    init {
+        out.setLevel(level)
+    }
+
+    private fun createZipEntry(name: String): ZipEntry {
+        val entry = ZipEntry(prefix + name)
+        entry.creationTime = timestamp
+        entry.lastAccessTime = timestamp
+        entry.lastModifiedTime = timestamp
+        return entry
+    }
+
+    override fun exists(archive: Int): Boolean {
+        throw UnsupportedOperationException()
+    }
+
+    override fun exists(archive: Int, group: Int): Boolean {
+        throw UnsupportedOperationException()
+    }
+
+    override fun list(): List<Int> {
+        throw UnsupportedOperationException()
+    }
+
+    override fun list(archive: Int): List<Int> {
+        throw UnsupportedOperationException()
+    }
+
+    override fun create(archive: Int) {
+        require(archive in 0..Store.MAX_ARCHIVE)
+
+        out.putNextEntry(createZipEntry("$archive/"))
+    }
+
+    override fun read(archive: Int, group: Int): ByteBuf {
+        throw UnsupportedOperationException()
+    }
+
+    override fun write(archive: Int, group: Int, buf: ByteBuf) {
+        require(archive in 0..Store.MAX_ARCHIVE)
+        require(group >= 0)
+        require(buf.readableBytes() <= Store.MAX_GROUP_SIZE)
+
+        out.putNextEntry(createZipEntry("$archive/$group.dat"))
+        buf.readBytes(out, buf.readableBytes())
+    }
+
+    override fun remove(archive: Int) {
+        throw UnsupportedOperationException()
+    }
+
+    override fun remove(archive: Int, group: Int) {
+        throw UnsupportedOperationException()
+    }
+
+    override fun flush() {
+        out.flush()
+    }
+
+    override fun close() {
+        out.close()
+    }
+}
diff --git a/cache/src/test/kotlin/org/openrs2/cache/DiskStoreZipWriterTest.kt b/cache/src/test/kotlin/org/openrs2/cache/DiskStoreZipWriterTest.kt
index b95d61e8..a970b83e 100644
--- a/cache/src/test/kotlin/org/openrs2/cache/DiskStoreZipWriterTest.kt
+++ b/cache/src/test/kotlin/org/openrs2/cache/DiskStoreZipWriterTest.kt
@@ -118,6 +118,6 @@ class DiskStoreZipWriterTest {
     }
 
     private companion object {
-        private val ROOT = Path.of(DiskStoreZipWriterTest::class.java.getResource("zip").toURI())
+        private val ROOT = Path.of(DiskStoreZipWriterTest::class.java.getResource("disk-store-zip").toURI())
     }
 }
diff --git a/cache/src/test/kotlin/org/openrs2/cache/FlatFileStoreZipWriterTest.kt b/cache/src/test/kotlin/org/openrs2/cache/FlatFileStoreZipWriterTest.kt
new file mode 100644
index 00000000..4e371c90
--- /dev/null
+++ b/cache/src/test/kotlin/org/openrs2/cache/FlatFileStoreZipWriterTest.kt
@@ -0,0 +1,125 @@
+package org.openrs2.cache
+
+import com.google.common.jimfs.Configuration
+import com.google.common.jimfs.Jimfs
+import io.netty.buffer.Unpooled
+import org.openrs2.buffer.copiedBuffer
+import org.openrs2.buffer.use
+import org.openrs2.util.io.recursiveEquals
+import java.io.OutputStream
+import java.nio.file.Files
+import java.nio.file.Path
+import java.util.zip.ZipOutputStream
+import kotlin.test.Test
+import kotlin.test.assertFailsWith
+import kotlin.test.assertTrue
+
+public class FlatFileStoreZipWriterTest {
+    @Test
+    fun testBounds() {
+        FlatFileStoreZipWriter(ZipOutputStream(OutputStream.nullOutputStream())).use { store ->
+            // create
+            assertFailsWith<IllegalArgumentException> {
+                store.create(-1)
+            }
+
+            store.create(0)
+            store.create(1)
+            store.create(254)
+            store.create(255)
+
+            assertFailsWith<IllegalArgumentException> {
+                store.create(256)
+            }
+
+            // write archive
+            assertFailsWith<IllegalArgumentException> {
+                store.write(-1, 0, Unpooled.EMPTY_BUFFER)
+            }
+
+            store.write(0, 0, Unpooled.EMPTY_BUFFER)
+            store.write(1, 0, Unpooled.EMPTY_BUFFER)
+            store.write(254, 0, Unpooled.EMPTY_BUFFER)
+            store.write(255, 0, Unpooled.EMPTY_BUFFER)
+
+            assertFailsWith<IllegalArgumentException> {
+                store.write(256, 0, Unpooled.EMPTY_BUFFER)
+            }
+
+            // write group
+            assertFailsWith<IllegalArgumentException> {
+                store.write(0, -1, Unpooled.EMPTY_BUFFER)
+            }
+
+            store.write(2, 0, Unpooled.EMPTY_BUFFER)
+            store.write(2, 1, Unpooled.EMPTY_BUFFER)
+        }
+    }
+
+    @Test
+    fun testUnsupported() {
+        FlatFileStoreZipWriter(ZipOutputStream(OutputStream.nullOutputStream())).use { store ->
+            assertFailsWith<UnsupportedOperationException> {
+                store.exists(0)
+            }
+
+            assertFailsWith<UnsupportedOperationException> {
+                store.exists(0, 0)
+            }
+
+            assertFailsWith<UnsupportedOperationException> {
+                store.list()
+            }
+
+            assertFailsWith<UnsupportedOperationException> {
+                store.list(0)
+            }
+
+            assertFailsWith<UnsupportedOperationException> {
+                store.read(0, 0)
+            }
+
+            assertFailsWith<UnsupportedOperationException> {
+                store.remove(0)
+            }
+
+            assertFailsWith<UnsupportedOperationException> {
+                store.remove(0, 0)
+            }
+        }
+    }
+
+    @Test
+    fun testWrite() {
+        Jimfs.newFileSystem(Configuration.forCurrentPlatform()).use { fs ->
+            val actual = fs.rootDirectories.first().resolve("zip")
+            Files.createDirectories(actual)
+
+            Files.newOutputStream(actual.resolve("cache.zip")).use { out ->
+                FlatFileStoreZipWriter(ZipOutputStream(out)).use { store ->
+                    store.create(0)
+
+                    copiedBuffer("OpenRS2").use { buf ->
+                        store.write(2, 0, buf)
+                    }
+
+                    copiedBuffer("OpenRS2".repeat(100)).use { buf ->
+                        store.write(2, 65535, buf)
+                    }
+
+                    copiedBuffer("OpenRS2".repeat(100)).use { buf ->
+                        store.write(2, 65536, buf)
+                    }
+                }
+            }
+
+            assertTrue(ROOT.recursiveEquals(actual))
+        }
+    }
+
+    private companion object {
+        private val ROOT = Path.of(
+            FlatFileStoreZipWriterTest::class.java.getResource("flat-file-store-zip").toURI()
+        )
+    }
+}
diff --git a/cache/src/test/resources/org/openrs2/cache/zip/cache.zip b/cache/src/test/resources/org/openrs2/cache/disk-store-zip/cache.zip
similarity index 100%
rename from cache/src/test/resources/org/openrs2/cache/zip/cache.zip
rename to cache/src/test/resources/org/openrs2/cache/disk-store-zip/cache.zip
diff --git a/cache/src/test/resources/org/openrs2/cache/flat-file-store-zip/cache.zip b/cache/src/test/resources/org/openrs2/cache/flat-file-store-zip/cache.zip
new file mode 100644
index 00000000..3655fd74
Binary files /dev/null and b/cache/src/test/resources/org/openrs2/cache/flat-file-store-zip/cache.zip differ