diff --git a/Cargo.lock b/Cargo.lock
index b12c063e..60dfd553 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -89,6 +89,10 @@ dependencies = [
 [[package]]
 name = "flat"
 version = "0.0.0"
+dependencies = [
+ "anyhow",
+ "thiserror",
+]
 
 [[package]]
 name = "hashbrown"
@@ -289,7 +293,6 @@ checksum = "d22af068fba1eb5edcb4aea19d382b2a3deb4c8f9d475c589b6ada9e0fd493ee"
 name = "uplc"
 version = "0.1.0"
 dependencies = [
- "anyhow",
  "combine",
  "flat",
  "hex",
diff --git a/crates/flat/Cargo.toml b/crates/flat/Cargo.toml
index e69e2d8a..1720ee99 100644
--- a/crates/flat/Cargo.toml
+++ b/crates/flat/Cargo.toml
@@ -5,4 +5,6 @@ edition = "2021"
 
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 
-[dependencies]
\ No newline at end of file
+[dependencies]
+anyhow = "1.0.57"
+thiserror = "1.0.31"
diff --git a/crates/flat/src/decode.rs b/crates/flat/src/decode.rs
index ac9d641c..0cd2e4ab 100644
--- a/crates/flat/src/decode.rs
+++ b/crates/flat/src/decode.rs
@@ -1,11 +1,17 @@
-use crate::{decoder::Decoder, filler::Filler};
+mod decoder;
+mod error;
+
+use crate::filler::Filler;
+
+pub use decoder::Decoder;
+pub use error::Error;
 
 pub trait Decode<'b>: Sized {
-    fn decode(d: &mut Decoder) -> Result<Self, String>;
+    fn decode(d: &mut Decoder) -> Result<Self, Error>;
 }
 
 impl Decode<'_> for Filler {
-    fn decode(d: &mut Decoder) -> Result<Filler, String> {
+    fn decode(d: &mut Decoder) -> Result<Filler, Error> {
         d.filler()?;
 
         Ok(Filler::FillerEnd)
@@ -13,43 +19,43 @@ impl Decode<'_> for Filler {
 }
 
 impl Decode<'_> for Vec<u8> {
-    fn decode(d: &mut Decoder) -> Result<Self, String> {
+    fn decode(d: &mut Decoder) -> Result<Self, Error> {
         d.bytes()
     }
 }
 
 impl Decode<'_> for u8 {
-    fn decode(d: &mut Decoder) -> Result<Self, String> {
+    fn decode(d: &mut Decoder) -> Result<Self, Error> {
         d.u8()
     }
 }
 
 impl Decode<'_> for isize {
-    fn decode(d: &mut Decoder) -> Result<Self, String> {
+    fn decode(d: &mut Decoder) -> Result<Self, Error> {
         d.integer()
     }
 }
 
 impl Decode<'_> for usize {
-    fn decode(d: &mut Decoder) -> Result<Self, String> {
+    fn decode(d: &mut Decoder) -> Result<Self, Error> {
         d.word()
     }
 }
 
 impl Decode<'_> for char {
-    fn decode(d: &mut Decoder) -> Result<Self, String> {
+    fn decode(d: &mut Decoder) -> Result<Self, Error> {
         d.char()
     }
 }
 
 impl Decode<'_> for String {
-    fn decode(d: &mut Decoder) -> Result<Self, String> {
+    fn decode(d: &mut Decoder) -> Result<Self, Error> {
         d.utf8()
     }
 }
 
 impl Decode<'_> for bool {
-    fn decode(d: &mut Decoder) -> Result<bool, String> {
+    fn decode(d: &mut Decoder) -> Result<bool, Error> {
         d.bool()
     }
 }
diff --git a/crates/flat/src/decoder.rs b/crates/flat/src/decode/decoder.rs
similarity index 67%
rename from crates/flat/src/decoder.rs
rename to crates/flat/src/decode/decoder.rs
index cc30197d..1fb02b73 100644
--- a/crates/flat/src/decoder.rs
+++ b/crates/flat/src/decode/decoder.rs
@@ -1,5 +1,7 @@
 use crate::{decode::Decode, zigzag};
 
+use super::Error;
+
 pub struct Decoder<'b> {
     buffer: &'b [u8],
     used_bits: i64,
@@ -15,35 +17,38 @@ impl<'b> Decoder<'b> {
         }
     }
 
-    pub fn decode<T: Decode<'b>>(&mut self) -> Result<T, String> {
+    /// Encode any type that implements [`Decode`].
+    pub fn decode<T: Decode<'b>>(&mut self) -> Result<T, Error> {
         T::decode(self)
     }
 
-    pub fn integer(&mut self) -> Result<isize, String> {
+    pub fn integer(&mut self) -> Result<isize, Error> {
         Ok(zigzag::to_isize(self.word()?))
     }
 
-    pub fn bool(&mut self) -> Result<bool, String> {
+    pub fn bool(&mut self) -> Result<bool, Error> {
         let current_byte = self.buffer[self.pos];
         let b = 0 != (current_byte & (128 >> self.used_bits));
         self.increment_buffer_by_bit();
         Ok(b)
     }
 
-    pub fn u8(&mut self) -> Result<u8, String> {
+    pub fn u8(&mut self) -> Result<u8, Error> {
         self.bits8(8)
     }
 
-    pub fn bytes(&mut self) -> Result<Vec<u8>, String> {
+    pub fn bytes(&mut self) -> Result<Vec<u8>, Error> {
         self.filler()?;
         self.byte_array()
     }
 
-    pub fn char(&mut self) -> Result<char, String> {
-        Ok(char::from_u32(self.word()? as u32).unwrap())
+    pub fn char(&mut self) -> Result<char, Error> {
+        let character = self.word()? as u32;
+
+        char::from_u32(character).ok_or(Error::DecodeChar(character))
     }
 
-    pub fn string(&mut self) -> Result<String, String> {
+    pub fn string(&mut self) -> Result<String, Error> {
         let mut s = String::new();
         while self.bit()? {
             s += &self.char()?.to_string();
@@ -51,17 +56,17 @@ impl<'b> Decoder<'b> {
         Ok(s)
     }
 
-    pub fn utf8(&mut self) -> Result<String, String> {
+    pub fn utf8(&mut self) -> Result<String, Error> {
         // TODO: Better Error Handling
-        Ok(String::from_utf8(Vec::<u8>::decode(self)?).unwrap())
+        String::from_utf8(Vec::<u8>::decode(self)?).map_err(Error::from)
     }
 
-    pub fn filler(&mut self) -> Result<(), String> {
+    pub fn filler(&mut self) -> Result<(), Error> {
         while self.zero()? {}
         Ok(())
     }
 
-    pub fn word(&mut self) -> Result<usize, String> {
+    pub fn word(&mut self) -> Result<usize, Error> {
         let mut leading_bit = 1;
         let mut final_word: usize = 0;
         let mut shl: usize = 0;
@@ -78,8 +83,8 @@ impl<'b> Decoder<'b> {
 
     pub fn decode_list_with<T: Decode<'b>>(
         &mut self,
-        decoder_func: for<'r> fn(&'r mut Decoder) -> Result<T, String>,
-    ) -> Result<Vec<T>, String> {
+        decoder_func: for<'r> fn(&'r mut Decoder) -> Result<T, Error>,
+    ) -> Result<Vec<T>, Error> {
         let mut vec_array: Vec<T> = Vec::new();
         while self.bit()? {
             vec_array.push(decoder_func(self)?)
@@ -87,46 +92,60 @@ impl<'b> Decoder<'b> {
         Ok(vec_array)
     }
 
-    fn zero(&mut self) -> Result<bool, String> {
+    fn zero(&mut self) -> Result<bool, Error> {
         let current_bit = self.bit()?;
+
         Ok(!current_bit)
     }
 
-    fn bit(&mut self) -> Result<bool, String> {
+    fn bit(&mut self) -> Result<bool, Error> {
         if self.pos >= self.buffer.len() {
-            return Err("DecoderState: Reached end of buffer".to_string());
+            return Err(Error::EndOfBuffer);
         }
+
         let b = self.buffer[self.pos] & (128 >> self.used_bits) > 0;
+
         self.increment_buffer_by_bit();
+
         Ok(b)
     }
 
-    fn byte_array(&mut self) -> Result<Vec<u8>, String> {
+    fn byte_array(&mut self) -> Result<Vec<u8>, Error> {
         if self.used_bits != 0 {
-            return Err("DecoderState.byteArray: Buffer is not byte aligned".to_string());
+            return Err(Error::BufferNotByteAligned);
         }
+
         self.ensure_bytes(1)?;
+
         let mut blk_len = self.buffer[self.pos];
+
         self.pos += 1;
+
         let mut blk_array: Vec<u8> = Vec::new();
+
         while blk_len != 0 {
             self.ensure_bytes(blk_len as usize + 1)?;
+
             let decoded_array = &self.buffer[self.pos..self.pos + blk_len as usize];
+
             blk_array.extend(decoded_array);
+
             self.pos += blk_len as usize;
+
             blk_len = self.buffer[self.pos];
         }
+
         Ok(blk_array)
     }
 
     // can decode up to a max of 8 bits
-    pub fn bits8(&mut self, num_bits: usize) -> Result<u8, String> {
+    pub fn bits8(&mut self, num_bits: usize) -> Result<u8, Error> {
         if num_bits > 8 {
-            return Err(
-                "Decoder.bits8: incorrect value of num_bits - must be less than 9".to_string(),
-            );
+            return Err(Error::IncorrectNumBits);
         }
+
         self.ensure_bits(num_bits)?;
+
         let unused_bits = 8 - self.used_bits as usize;
         let leading_zeroes = 8 - num_bits;
         let r = (self.buffer[self.pos] << self.used_bits as usize) >> leading_zeroes;
@@ -136,30 +155,28 @@ impl<'b> Decoder<'b> {
         } else {
             r
         };
+
         self.drop_bits(num_bits);
+
         Ok(x)
     }
 
-    fn ensure_bytes(&mut self, required_bytes: usize) -> Result<(), String> {
+    fn ensure_bytes(&mut self, required_bytes: usize) -> Result<(), Error> {
         if required_bytes as isize > self.buffer.len() as isize - self.pos as isize {
-            return Err(format!(
-                "DecoderState: Not enough data available: {:#?} - required bytes {}",
-                self.buffer, required_bytes
-            ));
+            Err(Error::NotEnoughBytes(required_bytes))
+        } else {
+            Ok(())
         }
-        Ok(())
     }
 
-    fn ensure_bits(&mut self, required_bits: usize) -> Result<(), String> {
+    fn ensure_bits(&mut self, required_bits: usize) -> Result<(), Error> {
         if required_bits as isize
             > (self.buffer.len() as isize - self.pos as isize) * 8 - self.used_bits as isize
         {
-            return Err(format!(
-                "DecoderState: Not enough data available: {:#?} - required bits {}",
-                self.buffer, required_bits
-            ));
+            Err(Error::NotEnoughBits(required_bits))
+        } else {
+            Ok(())
         }
-        Ok(())
     }
 
     fn drop_bits(&mut self, num_bits: usize) {
diff --git a/crates/flat/src/decode/error.rs b/crates/flat/src/decode/error.rs
new file mode 100644
index 00000000..fcf90b97
--- /dev/null
+++ b/crates/flat/src/decode/error.rs
@@ -0,0 +1,23 @@
+use thiserror::Error;
+
+#[derive(Error, Debug)]
+pub enum Error {
+    #[error("Reached end of buffer")]
+    EndOfBuffer,
+    #[error("Buffer is not byte aligned")]
+    BufferNotByteAligned,
+    #[error("Incorrect value of num_bits, must be less than 9")]
+    IncorrectNumBits,
+    #[error("Not enough data available, required {0} bytes")]
+    NotEnoughBytes(usize),
+    #[error("Not enough data available, required {0} bits")]
+    NotEnoughBits(usize),
+    #[error(transparent)]
+    DecodeUtf8(#[from] std::string::FromUtf8Error),
+    #[error("Decoding u32 to char {0}")]
+    DecodeChar(u32),
+    #[error("{0}")]
+    Message(String),
+    #[error(transparent)]
+    Custom(#[from] anyhow::Error),
+}
diff --git a/crates/flat/src/encode.rs b/crates/flat/src/encode.rs
index a2ae05bb..4d1706dc 100644
--- a/crates/flat/src/encode.rs
+++ b/crates/flat/src/encode.rs
@@ -1,11 +1,17 @@
-use crate::{encoder::Encoder, filler::Filler};
+mod encoder;
+mod error;
+
+use crate::filler::Filler;
+
+pub use encoder::Encoder;
+pub use error::Error;
 
 pub trait Encode {
-    fn encode(&self, e: &mut Encoder) -> Result<(), String>;
+    fn encode(&self, e: &mut Encoder) -> Result<(), Error>;
 }
 
 impl Encode for bool {
-    fn encode(&self, e: &mut Encoder) -> Result<(), String> {
+    fn encode(&self, e: &mut Encoder) -> Result<(), Error> {
         e.bool(*self);
 
         Ok(())
@@ -13,7 +19,7 @@ impl Encode for bool {
 }
 
 impl Encode for u8 {
-    fn encode(&self, e: &mut Encoder) -> Result<(), String> {
+    fn encode(&self, e: &mut Encoder) -> Result<(), Error> {
         e.u8(*self)?;
 
         Ok(())
@@ -21,15 +27,15 @@ impl Encode for u8 {
 }
 
 impl Encode for isize {
-    fn encode(&self, e: &mut Encoder) -> Result<(), String> {
-        e.integer(*self)?;
+    fn encode(&self, e: &mut Encoder) -> Result<(), Error> {
+        e.integer(*self);
 
         Ok(())
     }
 }
 
 impl Encode for usize {
-    fn encode(&self, e: &mut Encoder) -> Result<(), String> {
+    fn encode(&self, e: &mut Encoder) -> Result<(), Error> {
         e.word(*self);
 
         Ok(())
@@ -37,15 +43,15 @@ impl Encode for usize {
 }
 
 impl Encode for char {
-    fn encode(&self, e: &mut Encoder) -> Result<(), String> {
-        e.char(*self)?;
+    fn encode(&self, e: &mut Encoder) -> Result<(), Error> {
+        e.char(*self);
 
         Ok(())
     }
 }
 
 impl Encode for &str {
-    fn encode(&self, e: &mut Encoder) -> Result<(), String> {
+    fn encode(&self, e: &mut Encoder) -> Result<(), Error> {
         e.utf8(self)?;
 
         Ok(())
@@ -53,7 +59,7 @@ impl Encode for &str {
 }
 
 impl Encode for String {
-    fn encode(&self, e: &mut Encoder) -> Result<(), String> {
+    fn encode(&self, e: &mut Encoder) -> Result<(), Error> {
         e.utf8(self)?;
 
         Ok(())
@@ -61,7 +67,7 @@ impl Encode for String {
 }
 
 impl Encode for Vec<u8> {
-    fn encode(&self, e: &mut Encoder) -> Result<(), String> {
+    fn encode(&self, e: &mut Encoder) -> Result<(), Error> {
         e.bytes(self)?;
 
         Ok(())
@@ -69,7 +75,7 @@ impl Encode for Vec<u8> {
 }
 
 impl Encode for &[u8] {
-    fn encode(&self, e: &mut Encoder) -> Result<(), String> {
+    fn encode(&self, e: &mut Encoder) -> Result<(), Error> {
         e.bytes(self)?;
 
         Ok(())
@@ -77,7 +83,7 @@ impl Encode for &[u8] {
 }
 
 impl<T: Encode> Encode for Box<T> {
-    fn encode(&self, e: &mut Encoder) -> Result<(), String> {
+    fn encode(&self, e: &mut Encoder) -> Result<(), Error> {
         self.as_ref().encode(e)?;
 
         Ok(())
@@ -85,7 +91,7 @@ impl<T: Encode> Encode for Box<T> {
 }
 
 impl Encode for Filler {
-    fn encode(&self, e: &mut Encoder) -> Result<(), String> {
+    fn encode(&self, e: &mut Encoder) -> Result<(), Error> {
         e.filler();
 
         Ok(())
diff --git a/crates/flat/src/encoder.rs b/crates/flat/src/encode/encoder.rs
similarity index 85%
rename from crates/flat/src/encoder.rs
rename to crates/flat/src/encode/encoder.rs
index 099e7f25..4f372d63 100644
--- a/crates/flat/src/encoder.rs
+++ b/crates/flat/src/encode/encoder.rs
@@ -1,5 +1,7 @@
 use crate::{encode::Encode, zigzag};
 
+use super::Error;
+
 pub struct Encoder {
     pub buffer: Vec<u8>,
     // Int
@@ -24,12 +26,13 @@ impl Encoder {
     }
 
     /// Encode any type that implements [`Encode`].
-    pub fn encode<T: Encode>(&mut self, x: T) -> Result<&mut Self, String> {
+    pub fn encode<T: Encode>(&mut self, x: T) -> Result<&mut Self, Error> {
         x.encode(self)?;
+
         Ok(self)
     }
 
-    pub fn u8(&mut self, x: u8) -> Result<&mut Self, String> {
+    pub fn u8(&mut self, x: u8) -> Result<&mut Self, Error> {
         if self.used_bits == 0 {
             self.current_byte = x;
             self.next_word();
@@ -51,93 +54,54 @@ impl Encoder {
         self
     }
 
-    pub fn bytes(&mut self, x: &[u8]) -> Result<&mut Self, String> {
+    pub fn bytes(&mut self, x: &[u8]) -> Result<&mut Self, Error> {
         // use filler to write current buffer so bits used gets reset
         self.filler();
+
         self.byte_array(x)
     }
 
-    pub fn byte_array(&mut self, arr: &[u8]) -> Result<&mut Self, String> {
+    pub fn byte_array(&mut self, arr: &[u8]) -> Result<&mut Self, Error> {
         if self.used_bits != 0 {
-            return Err("Buffer is not byte aligned".to_string());
+            return Err(Error::BufferNotByteAligned);
         }
+
         self.write_blk(arr, &mut 0);
+
         Ok(self)
     }
 
-    pub fn integer(&mut self, i: isize) -> Result<&mut Self, String> {
+    pub fn integer(&mut self, i: isize) -> &mut Self {
         let i = zigzag::to_usize(i);
+
         self.word(i);
-        Ok(self)
+
+        self
     }
 
-    pub fn char(&mut self, c: char) -> Result<&mut Self, String> {
+    pub fn char(&mut self, c: char) -> &mut Self {
         self.word(c as usize);
-        Ok(self)
+
+        self
     }
+
     // TODO: Do we need this?
-    pub fn string(&mut self, s: &str) -> Result<&mut Self, String> {
+    pub fn string(&mut self, s: &str) -> &mut Self {
         for i in s.chars() {
             self.one();
-            self.char(i)?;
+            self.char(i);
         }
 
         self.zero();
 
-        Ok(self)
+        self
     }
 
-    pub fn utf8(&mut self, s: &str) -> Result<&mut Self, String> {
+    pub fn utf8(&mut self, s: &str) -> Result<&mut Self, Error> {
         self.bytes(s.as_bytes())
     }
 
-    fn zero(&mut self) {
-        if self.used_bits == 7 {
-            self.next_word();
-        } else {
-            self.used_bits += 1;
-        }
-    }
-
-    fn one(&mut self) {
-        if self.used_bits == 7 {
-            self.current_byte |= 1;
-            self.next_word();
-        } else {
-            self.current_byte |= 128 >> self.used_bits;
-            self.used_bits += 1;
-        }
-    }
-
-    fn byte_unaligned(&mut self, x: u8) {
-        let x_shift = self.current_byte | (x >> self.used_bits);
-        self.buffer.push(x_shift);
-
-        self.current_byte = x << (8 - self.used_bits);
-    }
-
-    fn next_word(&mut self) {
-        self.buffer.push(self.current_byte);
-
-        self.current_byte = 0;
-        self.used_bits = 0;
-    }
-
-    fn write_blk(&mut self, arr: &[u8], src_ptr: &mut usize) {
-        let src_len = arr.len() - *src_ptr;
-        let blk_len = src_len.min(255);
-        self.buffer.push(blk_len as u8);
-        if blk_len == 0 {
-            return;
-        }
-
-        self.buffer.extend(&arr[*src_ptr..blk_len]);
-
-        *src_ptr += blk_len;
-        self.write_blk(arr, src_ptr);
-    }
-
-    pub fn word(&mut self, c: usize) {
+    pub fn word(&mut self, c: usize) -> &mut Self {
         loop {
             let mut w = (c & 127) as u8;
             let c = c >> 7;
@@ -151,22 +115,26 @@ impl Encoder {
                 break;
             }
         }
+
+        self
     }
 
     pub fn encode_list_with(
         &mut self,
-        encoder_func: for<'r> fn(u8, &'r mut Encoder) -> Result<(), String>,
         list: Vec<u8>,
-    ) -> Result<(), String> {
+        encoder_func: for<'r> fn(u8, &'r mut Encoder) -> Result<(), Error>,
+    ) -> Result<&mut Self, Error> {
         for item in list {
             self.one();
             encoder_func(item, self)?;
         }
+
         self.zero();
-        Ok(())
+
+        Ok(self)
     }
 
-    pub fn bits(&mut self, num_bits: i64, val: u8) {
+    pub fn bits(&mut self, num_bits: i64, val: u8) -> &mut Self {
         match (num_bits, val) {
             (1, 0) => self.zero(),
             (1, 1) => self.one(),
@@ -207,10 +175,63 @@ impl Encoder {
                 }
             }
         }
+
+        self
     }
 
-    pub(crate) fn filler(&mut self) {
+    pub(crate) fn filler(&mut self) -> &mut Self {
         self.current_byte |= 1;
         self.next_word();
+
+        self
+    }
+
+    fn zero(&mut self) {
+        if self.used_bits == 7 {
+            self.next_word();
+        } else {
+            self.used_bits += 1;
+        }
+    }
+
+    fn one(&mut self) {
+        if self.used_bits == 7 {
+            self.current_byte |= 1;
+            self.next_word();
+        } else {
+            self.current_byte |= 128 >> self.used_bits;
+            self.used_bits += 1;
+        }
+    }
+
+    fn byte_unaligned(&mut self, x: u8) {
+        let x_shift = self.current_byte | (x >> self.used_bits);
+        self.buffer.push(x_shift);
+
+        self.current_byte = x << (8 - self.used_bits);
+    }
+
+    fn next_word(&mut self) {
+        self.buffer.push(self.current_byte);
+
+        self.current_byte = 0;
+        self.used_bits = 0;
+    }
+
+    fn write_blk(&mut self, arr: &[u8], src_ptr: &mut usize) {
+        let src_len = arr.len() - *src_ptr;
+        let blk_len = src_len.min(255);
+
+        self.buffer.push(blk_len as u8);
+
+        if blk_len == 0 {
+            return;
+        }
+
+        self.buffer.extend(&arr[*src_ptr..blk_len]);
+
+        *src_ptr += blk_len;
+
+        self.write_blk(arr, src_ptr);
     }
 }
diff --git a/crates/flat/src/encode/error.rs b/crates/flat/src/encode/error.rs
new file mode 100644
index 00000000..988dfda7
--- /dev/null
+++ b/crates/flat/src/encode/error.rs
@@ -0,0 +1,11 @@
+use thiserror::Error;
+
+#[derive(Error, Debug)]
+pub enum Error {
+    #[error("Buffer is not byte aligned")]
+    BufferNotByteAligned,
+    #[error("{0}")]
+    Message(String),
+    #[error(transparent)]
+    Custom(#[from] anyhow::Error),
+}
diff --git a/crates/flat/src/filler.rs b/crates/flat/src/filler.rs
index 7e33d2c1..0efe8db9 100644
--- a/crates/flat/src/filler.rs
+++ b/crates/flat/src/filler.rs
@@ -1,13 +1,13 @@
 pub enum Filler {
-    // FillerStart(Box<Filler>),
+    FillerStart(Box<Filler>),
     FillerEnd,
 }
 
-// impl Filler {
-//     pub fn len(&self) -> usize {
-//         match self {
-//             Filler::FillerStart(f) => f.len() + 1,
-//             Filler::FillerEnd => 1,
-//         }
-//     }
-// }
+impl Filler {
+    pub fn length(&self) -> usize {
+        match self {
+            Filler::FillerStart(f) => f.length() + 1,
+            Filler::FillerEnd => 1,
+        }
+    }
+}
diff --git a/crates/flat/src/lib.rs b/crates/flat/src/lib.rs
index 8a11995b..1a44fe46 100644
--- a/crates/flat/src/lib.rs
+++ b/crates/flat/src/lib.rs
@@ -1,31 +1,27 @@
 mod decode;
-mod decoder;
 mod encode;
-mod encoder;
-mod filler;
+pub mod filler;
 pub mod zigzag;
 
 pub mod en {
     pub use super::encode::*;
-    pub use super::encoder::*;
 }
 
 pub mod de {
     pub use super::decode::*;
-    pub use super::decoder::*;
 }
 
 pub trait Flat<'b>: en::Encode + de::Decode<'b> {
-    fn flat(&self) -> Result<Vec<u8>, String> {
+    fn flat(&self) -> Result<Vec<u8>, en::Error> {
         encode(self)
     }
 
-    fn unflat(bytes: &'b [u8]) -> Result<Self, String> {
+    fn unflat(bytes: &'b [u8]) -> Result<Self, de::Error> {
         decode(bytes)
     }
 }
 
-pub fn encode<T>(value: &T) -> Result<Vec<u8>, String>
+pub fn encode<T>(value: &T) -> Result<Vec<u8>, en::Error>
 where
     T: en::Encode,
 {
@@ -37,7 +33,7 @@ where
     Ok(e.buffer)
 }
 
-pub fn decode<'b, T>(bytes: &'b [u8]) -> Result<T, String>
+pub fn decode<'b, T>(bytes: &'b [u8]) -> Result<T, de::Error>
 where
     T: de::Decode<'b>,
 {
diff --git a/crates/uplc/Cargo.toml b/crates/uplc/Cargo.toml
index eccca392..ef1dcbc6 100644
--- a/crates/uplc/Cargo.toml
+++ b/crates/uplc/Cargo.toml
@@ -6,7 +6,6 @@ edition = "2021"
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 
 [dependencies]
-anyhow = "1.0.57"
 combine = "4.6.4"
 flat = { path = "../flat" }
 hex = "0.4.3"
diff --git a/crates/uplc/src/builtins.rs b/crates/uplc/src/builtins.rs
index fbcebfa6..00c9d723 100644
--- a/crates/uplc/src/builtins.rs
+++ b/crates/uplc/src/builtins.rs
@@ -1,3 +1,4 @@
+use flat::de;
 use strum_macros::EnumString;
 
 #[repr(u8)]
@@ -80,6 +81,8 @@ pub enum DefaultFunction {
 }
 
 impl TryFrom<u8> for DefaultFunction {
+    type Error = de::Error;
+
     fn try_from(v: u8) -> Result<Self, Self::Error> {
         match v {
             v if v == DefaultFunction::AddInteger as u8 => Ok(DefaultFunction::AddInteger),
@@ -184,9 +187,7 @@ impl TryFrom<u8> for DefaultFunction {
             v if v == DefaultFunction::MkPairData as u8 => Ok(DefaultFunction::MkPairData),
             v if v == DefaultFunction::MkNilData as u8 => Ok(DefaultFunction::MkNilData),
             v if v == DefaultFunction::MkNilPairData as u8 => Ok(DefaultFunction::MkNilPairData),
-            _ => Err("Default Function not found".to_string()),
+            _ => Err(de::Error::Message("Default Function not found".to_string())),
         }
     }
-
-    type Error = String;
 }
diff --git a/crates/uplc/src/debruijn.rs b/crates/uplc/src/debruijn.rs
index 294b184a..f37a6a6b 100644
--- a/crates/uplc/src/debruijn.rs
+++ b/crates/uplc/src/debruijn.rs
@@ -9,7 +9,7 @@ struct Level(usize);
 
 #[derive(Error, Debug)]
 pub enum Error {
-    #[error("Free Unique: `{0}`")]
+    #[error("Free Unique `{0}`")]
     FreeUnique(Unique),
 }
 
diff --git a/crates/uplc/src/flat.rs b/crates/uplc/src/flat.rs
index 846a8b0a..d4e16abf 100644
--- a/crates/uplc/src/flat.rs
+++ b/crates/uplc/src/flat.rs
@@ -1,8 +1,6 @@
-use anyhow::anyhow;
-
 use flat::{
-    de::{Decode, Decoder},
-    en::{Encode, Encoder},
+    de::{self, Decode, Decoder},
+    en::{self, Encode, Encoder},
     Flat,
 };
 
@@ -16,8 +14,8 @@ const CONST_TAG_WIDTH: u32 = 4;
 const TERM_TAG_WIDTH: u32 = 4;
 
 pub trait Binder<'b>: Encode + Decode<'b> {
-    fn binder_encode(&self, e: &mut Encoder) -> Result<(), String>;
-    fn binder_decode(d: &mut Decoder) -> Result<Self, String>;
+    fn binder_encode(&self, e: &mut Encoder) -> Result<(), en::Error>;
+    fn binder_decode(d: &mut Decoder) -> Result<Self, de::Error>;
 }
 
 impl<'b, T> Flat<'b> for Program<T> where T: Binder<'b> {}
@@ -28,12 +26,12 @@ where
 {
     // convenient so that people don't need to depend on the flat crate
     // directly to call programs flat function
-    pub fn to_flat(&self) -> anyhow::Result<Vec<u8>> {
-        self.flat().map_err(|err| anyhow!("{}", err))
+    pub fn to_flat(&self) -> Result<Vec<u8>, en::Error> {
+        self.flat()
     }
 
-    pub fn flat_hex(&self) -> anyhow::Result<String> {
-        let bytes = self.flat().map_err(|err| anyhow!("{}", err))?;
+    pub fn flat_hex(&self) -> Result<String, en::Error> {
+        let bytes = self.flat()?;
 
         let hex = hex::encode(&bytes);
 
@@ -45,7 +43,7 @@ impl<'b, T> Encode for Program<T>
 where
     T: Binder<'b>,
 {
-    fn encode(&self, e: &mut Encoder) -> Result<(), String> {
+    fn encode(&self, e: &mut Encoder) -> Result<(), en::Error> {
         let (major, minor, patch) = self.version;
 
         major.encode(e)?;
@@ -62,7 +60,7 @@ impl<'b, T> Decode<'b> for Program<T>
 where
     T: Binder<'b>,
 {
-    fn decode(d: &mut Decoder) -> Result<Self, String> {
+    fn decode(d: &mut Decoder) -> Result<Self, de::Error> {
         let version = (usize::decode(d)?, usize::decode(d)?, usize::decode(d)?);
         let term = Term::decode(d)?;
         Ok(Program { version, term })
@@ -73,7 +71,7 @@ impl<'b, T> Encode for Term<T>
 where
     T: Binder<'b>,
 {
-    fn encode(&self, e: &mut Encoder) -> Result<(), String> {
+    fn encode(&self, e: &mut Encoder) -> Result<(), en::Error> {
         match self {
             Term::Var(name) => {
                 encode_term_tag(0, e)?;
@@ -125,7 +123,7 @@ impl<'b, T> Decode<'b> for Term<T>
 where
     T: Binder<'b>,
 {
-    fn decode(d: &mut Decoder) -> Result<Self, String> {
+    fn decode(d: &mut Decoder) -> Result<Self, de::Error> {
         match decode_term_tag(d)? {
             0 => Ok(Term::Var(T::decode(d)?)),
             1 => Ok(Term::Delay(Box::new(Term::decode(d)?))),
@@ -142,13 +140,16 @@ where
             5 => Ok(Term::Force(Box::new(Term::decode(d)?))),
             6 => Ok(Term::Error),
             7 => Ok(Term::Builtin(DefaultFunction::decode(d)?)),
-            x => Err(format!("Unknown term constructor tag: {}", x)),
+            x => Err(de::Error::Message(format!(
+                "Unknown term constructor tag: {}",
+                x
+            ))),
         }
     }
 }
 
 impl Encode for &Constant {
-    fn encode(&self, e: &mut Encoder) -> Result<(), String> {
+    fn encode(&self, e: &mut Encoder) -> Result<(), en::Error> {
         match self {
             Constant::Integer(i) => {
                 encode_constant(0, e)?;
@@ -182,20 +183,23 @@ impl Encode for &Constant {
 }
 
 impl<'b> Decode<'b> for Constant {
-    fn decode(d: &mut Decoder) -> Result<Self, String> {
+    fn decode(d: &mut Decoder) -> Result<Self, de::Error> {
         match decode_constant(d)? {
             0 => Ok(Constant::Integer(isize::decode(d)?)),
             1 => Ok(Constant::ByteString(Vec::<u8>::decode(d)?)),
             2 => Ok(Constant::String(String::decode(d)?)),
             3 => Ok(Constant::Unit),
             4 => Ok(Constant::Bool(bool::decode(d)?)),
-            x => Err(format!("Unknown constant constructor tag: {}", x)),
+            x => Err(de::Error::Message(format!(
+                "Unknown constant constructor tag: {}",
+                x
+            ))),
         }
     }
 }
 
 impl Encode for Unique {
-    fn encode(&self, e: &mut Encoder) -> Result<(), String> {
+    fn encode(&self, e: &mut Encoder) -> Result<(), en::Error> {
         isize::from(*self).encode(e)?;
 
         Ok(())
@@ -203,13 +207,13 @@ impl Encode for Unique {
 }
 
 impl<'b> Decode<'b> for Unique {
-    fn decode(d: &mut Decoder) -> Result<Self, String> {
+    fn decode(d: &mut Decoder) -> Result<Self, de::Error> {
         Ok(isize::decode(d)?.into())
     }
 }
 
 impl Encode for Name {
-    fn encode(&self, e: &mut Encoder) -> Result<(), String> {
+    fn encode(&self, e: &mut Encoder) -> Result<(), en::Error> {
         self.text.encode(e)?;
         self.unique.encode(e)?;
 
@@ -218,7 +222,7 @@ impl Encode for Name {
 }
 
 impl<'b> Decode<'b> for Name {
-    fn decode(d: &mut Decoder) -> Result<Self, String> {
+    fn decode(d: &mut Decoder) -> Result<Self, de::Error> {
         Ok(Name {
             text: String::decode(d)?,
             unique: Unique::decode(d)?,
@@ -227,19 +231,19 @@ impl<'b> Decode<'b> for Name {
 }
 
 impl<'b> Binder<'b> for Name {
-    fn binder_encode(&self, e: &mut Encoder) -> Result<(), String> {
+    fn binder_encode(&self, e: &mut Encoder) -> Result<(), en::Error> {
         self.encode(e)?;
 
         Ok(())
     }
 
-    fn binder_decode(d: &mut Decoder) -> Result<Self, String> {
+    fn binder_decode(d: &mut Decoder) -> Result<Self, de::Error> {
         Name::decode(d)
     }
 }
 
 impl Encode for NamedDeBruijn {
-    fn encode(&self, e: &mut Encoder) -> Result<(), String> {
+    fn encode(&self, e: &mut Encoder) -> Result<(), en::Error> {
         self.text.encode(e)?;
         self.index.encode(e)?;
 
@@ -248,7 +252,7 @@ impl Encode for NamedDeBruijn {
 }
 
 impl<'b> Decode<'b> for NamedDeBruijn {
-    fn decode(d: &mut Decoder) -> Result<Self, String> {
+    fn decode(d: &mut Decoder) -> Result<Self, de::Error> {
         Ok(NamedDeBruijn {
             text: String::decode(d)?,
             index: DeBruijn::decode(d)?,
@@ -257,13 +261,13 @@ impl<'b> Decode<'b> for NamedDeBruijn {
 }
 
 impl<'b> Binder<'b> for NamedDeBruijn {
-    fn binder_encode(&self, e: &mut Encoder) -> Result<(), String> {
+    fn binder_encode(&self, e: &mut Encoder) -> Result<(), en::Error> {
         self.text.encode(e)?;
 
         Ok(())
     }
 
-    fn binder_decode(d: &mut Decoder) -> Result<Self, String> {
+    fn binder_decode(d: &mut Decoder) -> Result<Self, de::Error> {
         Ok(NamedDeBruijn {
             text: String::decode(d)?,
             index: DeBruijn::new(0),
@@ -272,7 +276,7 @@ impl<'b> Binder<'b> for NamedDeBruijn {
 }
 
 impl Encode for DeBruijn {
-    fn encode(&self, e: &mut Encoder) -> Result<(), String> {
+    fn encode(&self, e: &mut Encoder) -> Result<(), en::Error> {
         usize::from(*self).encode(e)?;
 
         Ok(())
@@ -280,23 +284,23 @@ impl Encode for DeBruijn {
 }
 
 impl<'b> Decode<'b> for DeBruijn {
-    fn decode(d: &mut Decoder) -> Result<Self, String> {
+    fn decode(d: &mut Decoder) -> Result<Self, de::Error> {
         Ok(usize::decode(d)?.into())
     }
 }
 
 impl<'b> Binder<'b> for DeBruijn {
-    fn binder_encode(&self, _: &mut Encoder) -> Result<(), String> {
+    fn binder_encode(&self, _: &mut Encoder) -> Result<(), en::Error> {
         Ok(())
     }
 
-    fn binder_decode(_d: &mut Decoder) -> Result<Self, String> {
+    fn binder_decode(_d: &mut Decoder) -> Result<Self, de::Error> {
         Ok(DeBruijn::new(0))
     }
 }
 
 impl Encode for DefaultFunction {
-    fn encode(&self, e: &mut Encoder) -> Result<(), String> {
+    fn encode(&self, e: &mut Encoder) -> Result<(), en::Error> {
         e.bits(BUILTIN_TAG_WIDTH as i64, self.clone() as u8);
 
         Ok(())
@@ -304,53 +308,55 @@ impl Encode for DefaultFunction {
 }
 
 impl<'b> Decode<'b> for DefaultFunction {
-    fn decode(d: &mut Decoder) -> Result<Self, String> {
+    fn decode(d: &mut Decoder) -> Result<Self, de::Error> {
         let builtin_tag = d.bits8(BUILTIN_TAG_WIDTH as usize)?;
         builtin_tag.try_into()
     }
 }
 
-fn encode_term_tag(tag: u8, e: &mut Encoder) -> Result<(), String> {
+fn encode_term_tag(tag: u8, e: &mut Encoder) -> Result<(), en::Error> {
     safe_encode_bits(TERM_TAG_WIDTH, tag, e)
 }
 
-fn decode_term_tag(d: &mut Decoder) -> Result<u8, String> {
+fn decode_term_tag(d: &mut Decoder) -> Result<u8, de::Error> {
     d.bits8(TERM_TAG_WIDTH as usize)
 }
 
-fn safe_encode_bits(num_bits: u32, byte: u8, e: &mut Encoder) -> Result<(), String> {
+fn safe_encode_bits(num_bits: u32, byte: u8, e: &mut Encoder) -> Result<(), en::Error> {
     if 2_u8.pow(num_bits) < byte {
-        Err(format!(
+        Err(en::Error::Message(format!(
             "Overflow detected, cannot fit {} in {} bits.",
             byte, num_bits
-        ))
+        )))
     } else {
         e.bits(num_bits as i64, byte);
         Ok(())
     }
 }
 
-pub fn encode_constant(tag: u8, e: &mut Encoder) -> Result<(), String> {
-    e.encode_list_with(encode_constant_tag, [tag].to_vec())
+pub fn encode_constant(tag: u8, e: &mut Encoder) -> Result<(), en::Error> {
+    e.encode_list_with([tag].to_vec(), encode_constant_tag)?;
+
+    Ok(())
 }
 
-pub fn decode_constant(d: &mut Decoder) -> Result<u8, String> {
+pub fn decode_constant(d: &mut Decoder) -> Result<u8, de::Error> {
     let u8_list = d.decode_list_with(decode_constant_tag)?;
     if u8_list.len() > 1 {
-        Err(
+        Err(de::Error::Message(
             "Improper encoding on constant tag. Should be list of one item encoded in 4 bits"
                 .to_string(),
-        )
+        ))
     } else {
         Ok(u8_list[0])
     }
 }
 
-pub fn encode_constant_tag(tag: u8, e: &mut Encoder) -> Result<(), String> {
+pub fn encode_constant_tag(tag: u8, e: &mut Encoder) -> Result<(), en::Error> {
     safe_encode_bits(CONST_TAG_WIDTH, tag, e)
 }
 
-pub fn decode_constant_tag(d: &mut Decoder) -> Result<u8, String> {
+pub fn decode_constant_tag(d: &mut Decoder) -> Result<u8, de::Error> {
     d.bits8(CONST_TAG_WIDTH as usize)
 }
 
diff --git a/crates/uplc/src/parser.rs b/crates/uplc/src/parser.rs
index 5e58f90b..c7371175 100644
--- a/crates/uplc/src/parser.rs
+++ b/crates/uplc/src/parser.rs
@@ -1,7 +1,9 @@
 use std::{collections::HashMap, str::FromStr};
 
 use combine::{
-    attempt, between, choice, many1,
+    attempt, between, choice,
+    error::StringStreamError,
+    many1,
     parser::{
         char::{alpha_num, digit, hex_digit, space, spaces, string},
         combinator::no_partial,
@@ -46,18 +48,15 @@ impl ParserState {
     }
 }
 
-pub fn program(src: &str) -> anyhow::Result<Program<Name>> {
+pub fn program(src: &str) -> Result<Program<Name>, StringStreamError> {
     let mut parser = program_();
 
-    let result = parser.parse(state::Stream {
+    let (program, _) = parser.parse(state::Stream {
         stream: position::Stream::new(src.trim()),
         state: ParserState::new(),
-    });
+    })?;
 
-    match result {
-        Ok((program, _)) => Ok(program),
-        Err(err) => Err(anyhow::anyhow!("{}", err)),
-    }
+    Ok(program)
 }
 
 fn program_<Input>() -> impl Parser<StateStream<Input>, Output = Program<Name>>