diff --git a/src/main/java/net/fabricmc/mappingio/MappingReader.java b/src/main/java/net/fabricmc/mappingio/MappingReader.java
index 93b5f22d..c76e20da 100644
--- a/src/main/java/net/fabricmc/mappingio/MappingReader.java
+++ b/src/main/java/net/fabricmc/mappingio/MappingReader.java
@@ -27,6 +27,7 @@
 import java.util.List;
 
 import net.fabricmc.mappingio.format.EnigmaReader;
+import net.fabricmc.mappingio.format.JarReader;
 import net.fabricmc.mappingio.format.MappingFormat;
 import net.fabricmc.mappingio.format.ProGuardReader;
 import net.fabricmc.mappingio.format.SrgReader;
@@ -69,6 +70,9 @@ public static MappingFormat detectFormat(Reader reader) throws IOException {
 		case "MD:":
 		case "FD:":
 			return MappingFormat.SRG;
+		case "PK\u0003": // zip/jar
+		case "MZ\ufffd": // windows exe
+			return MappingFormat.JAR;
 		}
 
 		String headerStr = String.valueOf(buffer, 0, pos);
@@ -141,8 +145,12 @@ public static void read(Path file, MappingFormat format, MappingVisitor visitor)
 		}
 
 		if (format.hasSingleFile()) {
-			try (Reader reader = Files.newBufferedReader(file)) {
-				read(reader, format, visitor);
+			if (format == MappingFormat.JAR) {
+				JarReader.read(file, visitor);
+			} else {
+				try (Reader reader = Files.newBufferedReader(file)) {
+					read(reader, format, visitor);
+				}
 			}
 		} else {
 			switch (format) {
diff --git a/src/main/java/net/fabricmc/mappingio/format/JarReader.java b/src/main/java/net/fabricmc/mappingio/format/JarReader.java
new file mode 100644
index 00000000..3d2882f4
--- /dev/null
+++ b/src/main/java/net/fabricmc/mappingio/format/JarReader.java
@@ -0,0 +1,101 @@
+/*
+ * Copyright (c) 2021 FabricMC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package net.fabricmc.mappingio.format;
+
+import java.io.IOException;
+import java.io.InputStream;
+import java.nio.file.Path;
+import java.nio.file.Paths;
+import java.util.ArrayList;
+import java.util.Enumeration;
+import java.util.zip.ZipEntry;
+import java.util.zip.ZipFile;
+
+import org.objectweb.asm.ClassReader;
+import org.objectweb.asm.ClassVisitor;
+import org.objectweb.asm.FieldVisitor;
+import org.objectweb.asm.MethodVisitor;
+import org.objectweb.asm.Opcodes;
+
+import net.fabricmc.mappingio.MappingVisitor;
+
+public class JarReader {
+	public static void read(Path path, MappingVisitor mappingVisitor) throws IOException {
+		AnalyzingVisitor analyzingVisitor = new AnalyzingVisitor(mappingVisitor);
+
+		ZipFile zipFile = new ZipFile(path.toFile());
+		Enumeration<? extends ZipEntry> entries = zipFile.entries();
+
+		mappingVisitor.visitNamespaces("jar", new ArrayList<String>());
+
+		while (entries.hasMoreElements()) {
+			ZipEntry entry = entries.nextElement();
+			String entryName = entry.getName();
+			String parentName = Paths.get("/", entryName).getParent().toString();
+
+			if (entryName.endsWith(".class") && !parentName.contains("-")) {
+				processClass(zipFile.getInputStream(entry), analyzingVisitor);
+			}
+		}
+	}
+
+	private static void processClass(InputStream inputStream, AnalyzingVisitor analyzingVisitor) throws IOException {
+		ClassReader reader = new ClassReader(inputStream);
+		reader.accept(analyzingVisitor, ClassReader.SKIP_CODE | ClassReader.SKIP_DEBUG);
+	}
+
+	private static final class AnalyzingVisitor extends ClassVisitor {
+		AnalyzingVisitor(MappingVisitor mappingVisitor) {
+			super(Integer.getInteger("mappingIo.asmApiVersion", Opcodes.ASM9));
+
+			this.mappingVisitor = mappingVisitor;
+		}
+
+		@Override
+		public void visit(int version, int access, String name, String signature, String superName, String[] interfaces) {
+			try {
+				mappingVisitor.visitClass(name);
+			} catch (IOException e) {
+				e.printStackTrace();
+			}
+		}
+
+		@Override
+		public FieldVisitor visitField(int access, String name, String descriptor, String signature, Object value) {
+			try {
+				mappingVisitor.visitField(name, descriptor);
+			} catch (IOException e) {
+				e.printStackTrace();
+			}
+
+			return null;
+		}
+
+		@Override
+		public MethodVisitor visitMethod(int access, String name, String descriptor, String signature, String[] exceptions) {
+			try {
+				mappingVisitor.visitMethod(name, descriptor);
+			} catch (IOException e) {
+				e.printStackTrace();
+			}
+
+			return null;
+		}
+
+		private final MappingVisitor mappingVisitor;
+	}
+}
diff --git a/src/main/java/net/fabricmc/mappingio/format/MappingFormat.java b/src/main/java/net/fabricmc/mappingio/format/MappingFormat.java
index ce8ae97f..877e3342 100644
--- a/src/main/java/net/fabricmc/mappingio/format/MappingFormat.java
+++ b/src/main/java/net/fabricmc/mappingio/format/MappingFormat.java
@@ -24,7 +24,8 @@ public enum MappingFormat {
 	SRG("SRG", "srg", false, false, false, false, false),
 	TSRG("TSRG", "tsrg", false, false, false, false, false),
 	TSRG2("TSRG2", "tsrg", true, false, false, true, false),
-	PROGUARD("ProGuard", "map", false, true, false, false, false);
+	PROGUARD("ProGuard", "map", false, true, false, false, false),
+	JAR("JAR", "jar", false, true, false, true, true);
 
 	MappingFormat(String name, String fileExt,
 			boolean hasNamespaces, boolean hasFieldDescriptors,