diff --git a/.github/workflows/master.yml b/.github/workflows/master.yml
index 6738b0b..5a759e4 100644
--- a/.github/workflows/master.yml
+++ b/.github/workflows/master.yml
@@ -8,7 +8,6 @@ on:
 
 jobs:
   build:
-
     runs-on: ubuntu-latest
 
     steps:
@@ -17,3 +16,25 @@ jobs:
       run: cargo build --verbose
     - name: Run tests
       run: cargo test --verbose
+    - name: Build serde
+      run: cargo build --verbose --features=derive
+    - name: Run tests serde
+      run: cargo test --verbose --features=derive
+    - name: Build no_std
+      run: cargo build --verbose --no-default-features
+    - name: Run tests no_std
+      run: cargo test --verbose --no-default-features
+    - name: Build no_std
+      run: cargo build --verbose --no-default-features --features=derive
+    - name: Run tests no_std
+      run: cargo test --verbose --no-default-features --features=derive
+    - name: Build defmt
+      run: cargo build --verbose --no-default-features --features=defmt
+    - name: Run tests defmt
+      run: cargo test --verbose --no-default-features --features=defmt
+    - name: Build defmt derive
+      run: cargo build --verbose --no-default-features --features=defmt --features=derive
+    - name: Run tests defmt derive
+      run: cargo test --verbose --no-default-features --features=defmt --features=derive
+
+
diff --git a/Cargo.toml b/Cargo.toml
index 2bc1424..0638cf0 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -18,13 +18,15 @@ license = "Apache-2.0"
 default = ["std"]
 
 # Implements serde::{Serialize,Deserialize} on mqttrs::Pid.
-derive = ["serde"]
-std = ["bytes", "bytes/std", "serde/std"]
+derive = ["serde", "heapless/serde"]
+std = ["bytes/std", "serde/std"]
+defmt = ["dep:defmt", "heapless/defmt-03"]
 
 [dependencies]
-bytes = { version = "1.0", default-features = false, optional = true }
+bytes = { version = "1.0", default-features = false}
 serde = { version = "1.0", features = ["derive"], optional = true }
-heapless = "0.7"
+heapless = { version = "0.8" }
+defmt = { version = "0.3.10", optional = true }
 
 [dev-dependencies]
 proptest = "0.10.0"
diff --git a/src/connect.rs b/src/connect.rs
index ef627e8..5991a46 100644
--- a/src/connect.rs
+++ b/src/connect.rs
@@ -1,10 +1,20 @@
+#[cfg(feature = "defmt")]
+use defmt::Format;
 use crate::{decoder::*, encoder::*, *};
+#[cfg(not(feature = "std"))]
+use heapless::String;
+#[cfg(feature = "std")]
+use std::string::String;
+use core::str::FromStr;
+
 
 /// Protocol version.
 ///
 /// Sent in [`Connect`] packet.
 ///
 /// [`Connect`]: struct.Connect.html
+///
+#[cfg_attr(feature = "defmt",derive(Format))]
 #[derive(Debug, Clone, Copy, PartialEq, Eq)]
 pub enum Protocol {
     /// [MQTT 3.1.1] is the most commonly implemented version. [MQTT 5] isn't yet supported my by
@@ -23,8 +33,8 @@ impl Protocol {
         match (name, level) {
             ("MQIsdp", 3) => Ok(Protocol::MQIsdp),
             ("MQTT", 4) => Ok(Protocol::MQTT311),
-            _ => Err(Error::InvalidProtocol(name.into(), level)),
-        }
+            _ => Err(Error::InvalidProtocol(String::from_str(name).unwrap(), 0)),
+    }
     }
     pub(crate) fn from_buffer<'a>(buf: &'a [u8], offset: &mut usize) -> Result<Self, Error> {
         let protocol_name = read_str(buf, offset)?;
@@ -61,6 +71,7 @@ impl Protocol {
 ///
 /// [Connect]: struct.Connect.html
 /// [MQTT 3.1.3.3]: http://docs.oasis-open.org/mqtt/mqtt/v3.1.1/os/mqtt-v3.1.1-os.html#_Toc398718031
+#[cfg_attr(feature = "defmt",derive(Format))]
 #[derive(Debug, Clone, PartialEq)]
 pub struct LastWill<'a> {
     pub topic: &'a str,
@@ -75,6 +86,7 @@ pub struct LastWill<'a> {
 ///
 /// [Connack]: struct.Connack.html
 /// [MQTT 3.2.2.3]: http://docs.oasis-open.org/mqtt/mqtt/v3.1.1/os/mqtt-v3.1.1-os.html#_Toc398718035
+#[cfg_attr(feature = "defmt",derive(Format))]
 #[derive(Debug, Clone, Copy, PartialEq)]
 pub enum ConnectReturnCode {
     Accepted,
@@ -111,6 +123,7 @@ impl ConnectReturnCode {
 /// Connect packet ([MQTT 3.1]).
 ///
 /// [MQTT 3.1]: http://docs.oasis-open.org/mqtt/mqtt/v3.1.1/os/mqtt-v3.1.1-os.html#_Toc398718028
+#[cfg_attr(feature = "defmt",derive(Format))]
 #[derive(Debug, Clone, PartialEq)]
 pub struct Connect<'a> {
     pub protocol: Protocol,
@@ -125,6 +138,7 @@ pub struct Connect<'a> {
 /// Connack packet ([MQTT 3.2]).
 ///
 /// [MQTT 3.2]: http://docs.oasis-open.org/mqtt/mqtt/v3.1.1/os/mqtt-v3.1.1-os.html#_Toc398718033
+#[cfg_attr(feature = "defmt",derive(Format))]
 #[derive(Debug, Clone, Copy, PartialEq)]
 pub struct Connack {
     pub session_present: bool,
diff --git a/src/decoder_test.rs b/src/decoder_test.rs
index b416433..00894a0 100644
--- a/src/decoder_test.rs
+++ b/src/decoder_test.rs
@@ -1,6 +1,7 @@
 use crate::*;
 use bytes::BytesMut;
 use subscribe::LimitedString;
+use core::str::FromStr;
 
 macro_rules! header {
     ($t:ident, $d:expr, $q:ident, $r:expr) => {
@@ -421,6 +422,7 @@ fn test_pub_comp() {
     };
 }
 
+#[cfg(feature = "std")]
 #[test]
 fn test_subscribe() {
     let mut data: &[u8] = &[
@@ -439,6 +441,25 @@ fn test_subscribe() {
     }
 }
 
+#[cfg(not(feature = "std"))]
+#[test]
+fn test_subscribe() {
+    let mut data: &[u8] = &[
+        0b10000010, 8, 0, 10, 0, 3, 'a' as u8, '/' as u8, 'b' as u8, 0,
+    ];
+    match decode_slice(&mut data) {
+        Ok(Some(Packet::Subscribe(s))) => {
+            assert_eq!(s.pid.get(), 10);
+            let t = SubscribeTopic {
+                topic_path: LimitedString::from_str("a/b").unwrap(),
+                qos: QoS::AtMostOnce,
+            };
+            assert_eq!(s.topics.get(0), Some(&t));
+        }
+        other => panic!("Failed decode: {:?}", other),
+    }
+}
+
 #[test]
 fn test_suback() {
     let mut data: &[u8] = &[0b10010000, 3, 0, 10, 0b00000010];
@@ -454,6 +475,7 @@ fn test_suback() {
     }
 }
 
+#[cfg(feature = "std")]
 #[test]
 fn test_unsubscribe() {
     let mut data: &[u8] = &[0b10100010, 5, 0, 10, 0, 1, 'a' as u8];
@@ -466,6 +488,19 @@ fn test_unsubscribe() {
     }
 }
 
+#[cfg(not(feature = "std"))]
+#[test]
+fn test_unsubscribe() {
+    let mut data: &[u8] = &[0b10100010, 5, 0, 10, 0, 1, 'a' as u8];
+    match decode_slice(&mut data) {
+        Ok(Some(Packet::Unsubscribe(a))) => {
+            assert_eq!(a.pid.get(), 10);
+            assert_eq!(a.topics.get(0), Some(&LimitedString::from_str("a").unwrap()));
+        }
+        other => panic!("Failed decode: {:?}", other),
+    }
+}
+
 #[test]
 fn test_unsub_ack() {
     let mut data: &[u8] = &[0b10110000, 2, 0, 10];
diff --git a/src/encoder_test.rs b/src/encoder_test.rs
index 918a6d3..b79c941 100644
--- a/src/encoder_test.rs
+++ b/src/encoder_test.rs
@@ -1,6 +1,7 @@
 use crate::*;
 use core::convert::TryFrom;
 use subscribe::{LimitedString, LimitedVec};
+use core::str::FromStr;
 
 #[cfg(feature = "std")]
 use bytes::BytesMut;
@@ -130,7 +131,7 @@ fn test_pubcomp() {
     // assert_decode!(Packet::Pubcomp(_), &packet);
     assert_decode_slice!(Packet::Pubcomp(_), &packet, 4);
 }
-
+#[cfg(feature = "std")]
 #[test]
 fn test_subscribe() {
     let stopic = SubscribeTopic {
@@ -143,6 +144,19 @@ fn test_subscribe() {
     assert_decode_slice!(Packet::Subscribe(_), &packet, 10);
 }
 
+#[cfg(not(feature = "std"))]
+#[test]
+fn test_subscribe() {
+    let stopic = SubscribeTopic {
+        topic_path: LimitedString::from_str("a/b").unwrap(),
+        qos: QoS::ExactlyOnce,
+    };
+    let topics: LimitedVec<SubscribeTopic> = [stopic].iter().cloned().collect();
+    let packet = Subscribe::new(Pid::try_from(345).unwrap(), topics).into();
+    // assert_decode!(Packet::Subscribe(_), &packet);
+    assert_decode_slice!(Packet::Subscribe(_), &packet, 10);
+}
+
 #[test]
 fn test_suback() {
     let return_codes = [SubscribeReturnCodes::Success(QoS::ExactlyOnce)]
@@ -156,7 +170,10 @@ fn test_suback() {
 
 #[test]
 fn test_unsubscribe() {
+    #[cfg(feature = "std")]
     let topics: LimitedVec<LimitedString> = [LimitedString::from("a/b")].iter().cloned().collect();
+    #[cfg(not(feature = "std"))]
+    let topics: LimitedVec<LimitedString> = [LimitedString::from_str("a/b").unwrap()].iter().cloned().collect();
 
     let packet = Unsubscribe::new(Pid::try_from(12321).unwrap(), topics).into();
     // assert_decode!(Packet::Unsubscribe(_), &packet);
diff --git a/src/packet.rs b/src/packet.rs
index d4c7a58..7c3b66a 100644
--- a/src/packet.rs
+++ b/src/packet.rs
@@ -1,3 +1,6 @@
+#[cfg(feature = "defmt")]
+use defmt::Format;
+
 use crate::*;
 
 /// Base enum for all MQTT packet types.
@@ -24,6 +27,7 @@ use crate::*;
 ///
 /// [`encode()`]: fn.encode.html
 /// [`decode_slice()`]: fn.decode_slice.html
+#[cfg_attr(feature = "defmt",derive(Format))]
 #[derive(Debug, Clone, PartialEq)]
 pub enum Packet<'a> {
     /// [MQTT 3.1](http://docs.oasis-open.org/mqtt/mqtt/v3.1.1/os/mqtt-v3.1.1-os.html#_Toc398718028)
@@ -107,6 +111,7 @@ packet_from_borrowed!(Connect, Publish);
 packet_from!(Suback, Connack, Subscribe, Unsubscribe);
 
 /// Packet type variant, without the associated data.
+#[cfg_attr(feature = "defmt",derive(Format))]
 #[derive(Debug, Copy, Clone, PartialEq, Eq, Hash, PartialOrd, Ord)]
 pub enum PacketType {
     Connect,
diff --git a/src/publish.rs b/src/publish.rs
index 54abbcc..f2b60b5 100644
--- a/src/publish.rs
+++ b/src/publish.rs
@@ -1,8 +1,11 @@
+#[cfg(feature = "defmt")]
+use defmt::Format;
 use crate::{decoder::*, encoder::*, *};
 
 /// Publish packet ([MQTT 3.3]).
 ///
 /// [MQTT 3.3]: http://docs.oasis-open.org/mqtt/mqtt/v3.1.1/os/mqtt-v3.1.1-os.html#_Toc398718037
+#[cfg_attr(feature = "defmt",derive(Format))]
 #[derive(Debug, Clone, PartialEq)]
 pub struct Publish<'a> {
     pub dup: bool,
diff --git a/src/subscribe.rs b/src/subscribe.rs
index b449db1..2aa7521 100644
--- a/src/subscribe.rs
+++ b/src/subscribe.rs
@@ -1,22 +1,27 @@
+#[cfg(feature = "defmt")]
+use defmt::Format;
 use crate::{decoder::*, encoder::*, *};
 #[cfg(feature = "derive")]
 use serde::{Deserialize, Serialize};
 
 #[cfg(feature = "std")]
-pub(crate) type LimitedVec<T> = std::vec::Vec<T>;
+pub type LimitedVec<T> = std::vec::Vec<T>;
 #[cfg(not(feature = "std"))]
-pub(crate) type LimitedVec<T> = heapless::Vec<T, 5>;
+pub type LimitedVec<T> = heapless::Vec<T, 5>;
 
 #[cfg(feature = "std")]
-pub(crate) type LimitedString = std::string::String;
+pub type LimitedString = std::string::String;
 #[cfg(not(feature = "std"))]
-pub(crate) type LimitedString = heapless::String<256>;
+pub type LimitedString = heapless::String<256>;
+
+use core::str::FromStr;
 
 /// Subscribe topic.
 ///
 /// [Subscribe] packets contain a `Vec` of those.
 ///
 /// [Subscribe]: struct.Subscribe.html
+#[cfg_attr(feature = "defmt",derive(Format))]
 #[derive(Debug, Clone, PartialEq)]
 #[cfg_attr(feature = "derive", derive(Serialize, Deserialize))]
 pub struct SubscribeTopic {
@@ -26,7 +31,7 @@ pub struct SubscribeTopic {
 
 impl SubscribeTopic {
     pub(crate) fn from_buffer(buf: &[u8], offset: &mut usize) -> Result<Self, Error> {
-        let topic_path = LimitedString::from(read_str(buf, offset)?);
+        let topic_path = LimitedString::from_str(read_str(buf, offset)?).unwrap();
         let qos = QoS::from_u8(buf[*offset])?;
         *offset += 1;
         Ok(SubscribeTopic { topic_path, qos })
@@ -38,6 +43,7 @@ impl SubscribeTopic {
 /// [Suback] packets contain a `Vec` of those.
 ///
 /// [Suback]: struct.Subscribe.html
+#[cfg_attr(feature = "defmt",derive(Format))]
 #[derive(Debug, Clone, Copy, PartialEq, Eq)]
 pub enum SubscribeReturnCodes {
     Success(QoS),
@@ -67,6 +73,7 @@ impl SubscribeReturnCodes {
 /// Subscribe packet ([MQTT 3.8]).
 ///
 /// [MQTT 3.8]: http://docs.oasis-open.org/mqtt/mqtt/v3.1.1/os/mqtt-v3.1.1-os.html#_Toc398718063
+#[cfg_attr(feature = "defmt",derive(Format))]
 #[derive(Debug, Clone, PartialEq)]
 pub struct Subscribe {
     pub pid: Pid,
@@ -76,6 +83,7 @@ pub struct Subscribe {
 /// Subsack packet ([MQTT 3.9]).
 ///
 /// [MQTT 3.9]: http://docs.oasis-open.org/mqtt/mqtt/v3.1.1/os/mqtt-v3.1.1-os.html#_Toc398718068
+#[cfg_attr(feature = "defmt",derive(Format))]
 #[derive(Debug, Clone, PartialEq)]
 pub struct Suback {
     pub pid: Pid,
@@ -85,6 +93,7 @@ pub struct Suback {
 /// Unsubscribe packet ([MQTT 3.10]).
 ///
 /// [MQTT 3.10]: http://docs.oasis-open.org/mqtt/mqtt/v3.1.1/os/mqtt-v3.1.1-os.html#_Toc398718072
+#[cfg_attr(feature = "defmt",derive(Format))]
 #[derive(Debug, Clone, PartialEq)]
 pub struct Unsubscribe {
     pub pid: Pid,
@@ -155,7 +164,7 @@ impl Unsubscribe {
 
         let mut topics = LimitedVec::new();
         while *offset < payload_end {
-            let _res = topics.push(LimitedString::from(read_str(buf, offset)?));
+            let _res = topics.push(LimitedString::from_str(read_str(buf, offset)?).unwrap());
 
             #[cfg(not(feature = "std"))]
             _res.map_err(|_| Error::InvalidLength)?;
diff --git a/src/utils.rs b/src/utils.rs
index c0d5f59..47357d0 100644
--- a/src/utils.rs
+++ b/src/utils.rs
@@ -1,3 +1,7 @@
+#[cfg(feature = "defmt")]
+use defmt::{Format};
+
+
 use crate::encoder::write_u16;
 use core::{convert::TryFrom, fmt, num::NonZeroU16};
 
@@ -15,6 +19,9 @@ use std::{
 ///
 /// [`encode()`]: fn.encode.html
 /// [`decode()`]: fn.decode.html
+
+
+#[cfg_attr(feature = "defmt",derive(Format))]
 #[derive(Debug, Clone, PartialEq, Eq)]
 pub enum Error {
     /// Not enough space in the write buffer.
@@ -40,7 +47,7 @@ pub enum Error {
     /// length rather than a buffer size issue.
     InvalidLength,
     /// Trying to decode a non-utf8 string.
-    InvalidString(core::str::Utf8Error),
+    InvalidString(#[cfg_attr(feature = "defmt",defmt(Debug2Format))] core::str::Utf8Error),
     /// Catch-all error when converting from `std::io::Error`.
     ///
     /// Note: Only available when std is available.
@@ -106,6 +113,8 @@ impl From<IoError> for Error {
 /// [`QoS::AtLeastOne` or `QoS::ExactlyOnce`]: enum.QoS.html
 /// [MQTT-2.3.1-1]: https://docs.oasis-open.org/mqtt/mqtt/v3.1.1/os/mqtt-v3.1.1-os.html#_Toc398718025
 /// [MQTT-2.2.1-3]: https://docs.oasis-open.org/mqtt/mqtt/v5.0/os/mqtt-v5.0-os.html#_Toc3901026
+
+#[cfg_attr(feature = "defmt",derive(Format))]
 #[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
 #[cfg_attr(feature = "derive", derive(Serialize, Deserialize))]
 pub struct Pid(NonZeroU16);
@@ -186,6 +195,7 @@ impl TryFrom<u16> for Pid {
 /// Packet delivery [Quality of Service] level.
 ///
 /// [Quality of Service]: http://docs.oasis-open.org/mqtt/mqtt/v3.1.1/os/mqtt-v3.1.1-os.html#_Toc398718099
+#[cfg_attr(feature = "defmt",derive(Format))]
 #[derive(Debug, Clone, Copy, PartialEq, Eq)]
 #[cfg_attr(feature = "derive", derive(Serialize, Deserialize))]
 pub enum QoS {
@@ -223,6 +233,7 @@ impl QoS {
 /// [`Publish`]: struct.Publish.html
 /// [`QoS`]: enum.QoS.html
 /// [`Pid`]: struct.Pid.html
+#[cfg_attr(feature = "defmt",derive(Format))]
 #[derive(Debug, Clone, Copy, PartialEq, Eq)]
 #[cfg_attr(feature = "derive", derive(Serialize, Deserialize))]
 pub enum QosPid {