diff --git a/Cargo.lock b/Cargo.lock
index 140aa01..e3a1a14 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -2,6 +2,49 @@
 # It is not intended for manual editing.
 version = 4
 
+[[package]]
+name = "adler2"
+version = "2.0.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "320119579fcad9c21884f5c4861d16174d0e06250625266f50fe6898340abefa"
+
+[[package]]
+name = "cfg-if"
+version = "1.0.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "2fd1289c04a9ea8cb22300a459a72a385d7c73d3259e2ed7dcb2af674838cfa9"
+
+[[package]]
+name = "crc32fast"
+version = "1.5.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9481c1c90cbf2ac953f07c8d4a58aa3945c425b7185c9154d67a65e4230da511"
+dependencies = [
+ "cfg-if",
+]
+
+[[package]]
+name = "flate2"
+version = "1.1.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "4a3d7db9596fecd151c5f638c0ee5d5bd487b6e0ea232e5dc96d5250f6f94b1d"
+dependencies = [
+ "crc32fast",
+ "miniz_oxide",
+]
+
+[[package]]
+name = "miniz_oxide"
+version = "0.8.9"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "1fa76a2c86f704bdb222d66965fb3d63269ce38518b83cb0575fca855ebb6316"
+dependencies = [
+ "adler2",
+]
+
 [[package]]
 name = "nbt"
 version = "0.1.0"
+dependencies = [
+ "flate2",
+]
diff --git a/Cargo.toml b/Cargo.toml
index a81a699..9659195 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -4,3 +4,4 @@ version = "0.1.0"
 edition = "2024"
 
 [dependencies]
+flate2 = "1.1.2"
diff --git a/src/io.rs b/src/io.rs
index 77f4b4a..c7194d4 100644
--- a/src/io.rs
+++ b/src/io.rs
@@ -4,12 +4,28 @@ use std::{
 };
 
 use crate::{Tag, TagId};
+use flate2::{Compression, read::GzDecoder, write::GzEncoder};
 
 /// Binary reader for NBT format
 pub struct Reader<R: Read> {
     inner: R,
 }
 
+// --- Reader gzip ---
+impl<R: Read> Reader<GzDecoder<R>> {
+    pub fn from_gzip(inner: R) -> Self {
+        Reader {
+            inner: GzDecoder::new(inner),
+        }
+    }
+}
+impl<W: Write> Writer<GzEncoder<W>> {
+    pub fn to_gzip(inner: W) -> Self {
+        Writer {
+            inner: GzEncoder::new(inner, Compression::default()),
+        }
+    }
+}
 impl<R: Read> Reader<R> {
     pub fn new(inner: R) -> Self {
         Reader { inner }
@@ -134,13 +150,22 @@ impl<R: Read> Reader<R> {
         Ok(i64::from_be_bytes(buf))
     }
     fn read_f32(&mut self) -> Result<f32> {
-        Ok(f32::from_bits(self.read_i32()? as u32))
+        let mut b = [0u8; 4];
+        self.inner.read_exact(&mut b)?;
+        Ok(f32::from_bits(u32::from_be_bytes(b)))
     }
     fn read_f64(&mut self) -> Result<f64> {
-        Ok(f64::from_bits(self.read_i64()? as u64))
+        let mut b = [0u8; 8];
+        self.inner.read_exact(&mut b)?;
+        Ok(f64::from_bits(u64::from_be_bytes(b)))
+    }
+    fn read_u16(&mut self) -> Result<u16> {
+        let mut b = [0u8; 2];
+        self.inner.read_exact(&mut b)?;
+        Ok(u16::from_be_bytes(b))
     }
     fn read_string(&mut self) -> Result<String> {
-        let len = self.read_i16()? as usize;
+        let len = self.read_u16()? as usize;
         let mut buf = vec![0u8; len];
         self.inner.read_exact(&mut buf)?;
         String::from_utf8(buf).map_err(|e| Error::new(ErrorKind::InvalidData, e))
@@ -240,14 +265,17 @@ impl<W: Write> Writer<W> {
         self.inner.write_all(&v.to_be_bytes())
     }
     fn write_f32(&mut self, v: f32) -> Result<()> {
-        self.write_i32(v.to_bits() as i32)
+        self.inner.write_all(&v.to_bits().to_be_bytes())
     }
     fn write_f64(&mut self, v: f64) -> Result<()> {
-        self.write_i64(v.to_bits() as i64)
+        self.inner.write_all(&v.to_bits().to_be_bytes())
     }
     fn write_string(&mut self, s: &str) -> Result<()> {
         let bytes = s.as_bytes();
-        self.write_i16(bytes.len() as i16)?;
+        if bytes.len() > u16::MAX as usize {
+            return Err(Error::new(ErrorKind::InvalidInput, "string too long"));
+        }
+        self.inner.write_all(&(bytes.len() as u16).to_be_bytes())?;
         self.inner.write_all(bytes)
     }
 }
diff --git a/src/test.rs b/src/test.rs
index e216afb..d7dc072 100644
--- a/src/test.rs
+++ b/src/test.rs
@@ -164,3 +164,324 @@ fn roundtrip_compound() {
     let decoded = read_nbt(&buf[..]).unwrap();
     assert_eq!(decoded, root);
 }
+
+// ---------------------------------------------------------------------------------
+#[cfg(test)]
+mod tests {
+    use std::io::{Cursor, Read};
+
+    use flate2::bufread::GzDecoder;
+
+    use crate::{Reader, Tag, Writer};
+
+    fn sample_level_compound() -> Tag {
+        use std::collections::HashMap;
+        let mut entries = HashMap::new();
+        entries.insert(
+            "DataVersion".into(),
+            Tag::Int {
+                name: Some("DataVersion".into()),
+                value: 3837,
+            },
+        );
+        entries.insert(
+            "LevelName".into(),
+            Tag::String {
+                name: Some("LevelName".into()),
+                value: "test".into(),
+            },
+        );
+        entries.insert(
+            "GameType".into(),
+            Tag::Int {
+                name: Some("GameType".into()),
+                value: 0,
+            },
+        );
+        entries.insert(
+            "Difficulty".into(),
+            Tag::Byte {
+                name: Some("Difficulty".into()),
+                value: 2,
+            },
+        );
+        entries.insert(
+            "hardcore".into(),
+            Tag::Byte {
+                name: Some("hardcore".into()),
+                value: 0,
+            },
+        );
+        entries.insert(
+            "allowCommands".into(),
+            Tag::Byte {
+                name: Some("allowCommands".into()),
+                value: 1,
+            },
+        );
+        entries.insert(
+            "SpawnX".into(),
+            Tag::Int {
+                name: Some("SpawnX".into()),
+                value: 0,
+            },
+        );
+        entries.insert(
+            "SpawnY".into(),
+            Tag::Int {
+                name: Some("SpawnY".into()),
+                value: 64,
+            },
+        );
+        entries.insert(
+            "SpawnZ".into(),
+            Tag::Int {
+                name: Some("SpawnZ".into()),
+                value: 0,
+            },
+        );
+
+        let list = Tag::List {
+            name: Some("TestList".into()),
+            element_id: 3,
+            elements: vec![
+                Tag::Int {
+                    name: None,
+                    value: 1,
+                },
+                Tag::Int {
+                    name: None,
+                    value: 2,
+                },
+                Tag::Int {
+                    name: None,
+                    value: 3,
+                },
+            ],
+        };
+        entries.insert("TestList".into(), list);
+        Tag::Compound {
+            name: Some("Data".into()),
+            entries,
+        }
+    }
+
+    fn write_uncompressed(tag: &Tag) -> Vec<u8> {
+        let mut buf = Cursor::new(Vec::new());
+        let mut w = Writer::new(&mut buf);
+        w.write_tag(tag).unwrap();
+        buf.into_inner()
+    }
+
+    fn read_uncompressed(bytes: &[u8]) -> Tag {
+        let mut r = Reader::new(Cursor::new(bytes));
+        r.read_tag().unwrap()
+    }
+
+    #[test]
+    fn roundtrip_uncompressed() {
+        let root = sample_level_compound();
+        let bytes = write_uncompressed(&root);
+        let back = read_uncompressed(&bytes);
+
+        match back {
+            Tag::Compound { name, .. } => assert_eq!(name.as_deref(), Some("Data")),
+            _ => panic!("root not a Compound"),
+        }
+    }
+
+    #[test]
+    fn list_elements_have_no_names() {
+        let root = sample_level_compound();
+        let bytes = write_uncompressed(&root);
+        let back = read_uncompressed(&bytes);
+        let Tag::Compound { entries, .. } = back else {
+            panic!("not compound");
+        };
+        let Tag::List {
+            element_id,
+            elements,
+            ..
+        } = entries.get("TestList").expect("missing TestList")
+        else {
+            panic!("not list");
+        };
+        assert_eq!(*element_id, 3);
+        assert_eq!(elements.len(), 3);
+        for e in elements {
+            match e {
+                Tag::Int { name, value } => {
+                    assert!(name.is_none());
+                    assert!(*value >= 1 && *value <= 3);
+                }
+                _ => panic!("list element not Int"),
+            }
+        }
+    }
+
+    #[test]
+    fn string_length_u16_boundary() {
+        let s = "a".repeat(300);
+        let tag = Tag::String {
+            name: Some("S".into()),
+            value: s.clone(),
+        };
+        let root = Tag::Compound {
+            name: Some("Data".into()),
+            entries: {
+                let mut m = std::collections::HashMap::new();
+                m.insert("S".into(), tag);
+                m
+            },
+        };
+        let bytes = write_uncompressed(&root);
+        let back = read_uncompressed(&bytes);
+        let Tag::Compound { entries, .. } = back else {
+            panic!("not compound");
+        };
+        let Tag::String { value, .. } = entries.get("S").expect("missing S") else {
+            panic!("not string");
+        };
+        assert_eq!(value, &s);
+    }
+
+    #[test]
+    fn roundtrip_gzip() {
+        let root = sample_level_compound();
+
+        let mut out = Vec::new();
+        {
+            let cursor = Cursor::new(&mut out);
+            let mut w = Writer::to_gzip(cursor);
+            w.write_tag(&root).unwrap();
+        }
+
+        assert!(out.len() >= 2);
+        assert_eq!(out[0], 0x1f);
+        assert_eq!(out[1], 0x8b);
+
+        let mut r = Reader::from_gzip(Cursor::new(&out));
+        let back = r.read_tag().unwrap();
+        match back {
+            Tag::Compound { name, .. } => assert_eq!(name.as_deref(), Some("Data")),
+            _ => panic!("root not a Compound"),
+        }
+    }
+
+    #[test]
+    fn error_on_unknown_tag_id() {
+        let mut raw = Vec::new();
+        raw.push(99u8);
+        raw.extend_from_slice(&0u16.to_be_bytes());
+        let mut r = Reader::new(Cursor::new(raw));
+        let err = r.read_tag().err().expect("should error");
+        assert_eq!(err.kind(), std::io::ErrorKind::InvalidData);
+    }
+
+    #[test]
+    fn compound_end_marker_required() {
+        let mut raw = Vec::new();
+        raw.push(10u8);
+        raw.extend_from_slice(&(4u16.to_be_bytes()));
+        raw.extend_from_slice(b"Data");
+
+        let mut r = Reader::new(Cursor::new(raw));
+        let res = r.read_tag();
+        assert!(res.is_err(), "Reader should fail on missing TAG_End");
+    }
+
+    #[test]
+    fn float_and_double_are_be() {
+        let mut entries = std::collections::HashMap::new();
+        entries.insert(
+            "F".into(),
+            Tag::Float {
+                name: Some("F".into()),
+                value: 1234.5f32,
+            },
+        );
+        entries.insert(
+            "D".into(),
+            Tag::Double {
+                name: Some("D".into()),
+                value: -0.25f64,
+            },
+        );
+        let root = Tag::Compound {
+            name: Some("Data".into()),
+            entries,
+        };
+
+        let bytes = write_uncompressed(&root);
+
+        let back = read_uncompressed(&bytes);
+        let Tag::Compound { entries, .. } = back else {
+            panic!("not compound");
+        };
+        let Tag::Float { value: f, .. } = entries.get("F").unwrap() else {
+            panic!("F missing");
+        };
+        let Tag::Double { value: d, .. } = entries.get("D").unwrap() else {
+            panic!("D missing");
+        };
+        assert!((*f - 1234.5).abs() < 1e-4);
+        assert!((*d + 0.25).abs() < 1e-12);
+    }
+
+    #[test]
+    fn int_long_arrays_roundtrip() {
+        let ia = (0..16).map(|i| i - 8).collect::<Vec<_>>();
+        let la = (0..8).map(|i| (i as i64) * (1 << 33)).collect::<Vec<_>>();
+        let mut entries = std::collections::HashMap::new();
+        entries.insert(
+            "IA".into(),
+            Tag::IntArray {
+                name: Some("IA".into()),
+                value: ia.clone(),
+            },
+        );
+        entries.insert(
+            "LA".into(),
+            Tag::LongArray {
+                name: Some("LA".into()),
+                value: la.clone(),
+            },
+        );
+        let root = Tag::Compound {
+            name: Some("Data".into()),
+            entries,
+        };
+
+        let bytes = write_uncompressed(&root);
+        let back = read_uncompressed(&bytes);
+
+        let Tag::Compound { entries, .. } = back else {
+            panic!("not compound");
+        };
+        let Tag::IntArray { value: ia2, .. } = entries.get("IA").unwrap() else {
+            panic!("IA");
+        };
+        let Tag::LongArray { value: la2, .. } = entries.get("LA").unwrap() else {
+            panic!("LA");
+        };
+        assert_eq!(ia2, &ia);
+        assert_eq!(la2, &la);
+    }
+
+    #[test]
+    fn gzip_stream_is_valid_by_gzdecoder() {
+        let root = sample_level_compound();
+        let mut out = Vec::new();
+        {
+            let cursor = Cursor::new(&mut out);
+            let mut w = Writer::to_gzip(cursor);
+            w.write_tag(&root).unwrap();
+        }
+        let mut dec = GzDecoder::new(Cursor::new(&out));
+        let mut raw = Vec::new();
+        dec.read_to_end(&mut raw).unwrap();
+        assert!(!raw.is_empty());
+
+        assert_eq!(raw[0], 10u8);
+    }
+}