diff --git a/Cargo.lock b/Cargo.lock
index f535543..5fccc55 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -2,6 +2,15 @@
 # It is not intended for manual editing.
 version = 4
 
+[[package]]
+name = "aho-corasick"
+version = "1.1.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ddd31a130427c27518df266943a5308ed92d4b226cc639f5a8f1002816174301"
+dependencies = [
+ "memchr",
+]
+
 [[package]]
 name = "android_system_properties"
 version = "0.1.5"
@@ -1355,6 +1364,35 @@ dependencies = [
  "bitflags 2.9.4",
 ]
 
+[[package]]
+name = "regex"
+version = "1.12.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "843bc0191f75f3e22651ae5f1e72939ab2f72a4bc30fa80a066bd66edefc24d4"
+dependencies = [
+ "aho-corasick",
+ "memchr",
+ "regex-automata",
+ "regex-syntax",
+]
+
+[[package]]
+name = "regex-automata"
+version = "0.4.13"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "5276caf25ac86c8d810222b3dbb938e512c55c6831a10f3e6ed1c93b84041f1c"
+dependencies = [
+ "aho-corasick",
+ "memchr",
+ "regex-syntax",
+]
+
+[[package]]
+name = "regex-syntax"
+version = "0.8.8"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7a2d987857b319362043e95f5353c0535c1f58eec5336fdfcf626430af7def58"
+
 [[package]]
 name = "reqwest"
 version = "0.12.24"
@@ -1838,6 +1876,7 @@ dependencies = [
  "log",
  "log4rs",
  "notify",
+ "regex",
  "reqwest",
  "serde",
  "thiserror",
diff --git a/Cargo.toml b/Cargo.toml
index adfb9a9..a94efbd 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -25,3 +25,4 @@ url = "2.5.7"
 clap = { version = "4.5.51", features = ["derive"] }
 notify = "8.2.0"
 arc-swap = "1.7.1"
+regex = "1.12.2"
diff --git a/src/ast_compiler.rs b/src/ast_compiler.rs
index fd16802..2f270f9 100644
--- a/src/ast_compiler.rs
+++ b/src/ast_compiler.rs
@@ -146,7 +146,7 @@ impl AstCompiler {
                 self.query_guard_expr(symbol_table)
             } else {
                 Err(self.raise(Expected("-> or ?")))
-            }
+            };
         }
         Ok(Stop {
             line: self.peek().line,
@@ -803,6 +803,19 @@ pub struct Parameter {
     pub(crate) var_type: TokenType,
 }
 
+impl Parameter {
+    pub(crate) fn new(name: impl Into<String>, value_type: TokenType) -> Self {
+        Self {
+            name: Token {
+                token_type: TokenType::StringType,
+                lexeme: name.into(),
+                line: 0,
+            },
+            var_type: value_type,
+        }
+    }
+}
+
 #[derive(Debug, Clone)]
 pub enum Expression {
     Binary {
diff --git a/src/builtins/mod.rs b/src/builtins/mod.rs
index 18dd8bc..0204599 100644
--- a/src/builtins/mod.rs
+++ b/src/builtins/mod.rs
@@ -1,13 +1,39 @@
 mod string;
 
+use crate::builtins::string::string_methods;
+use crate::errors::{CompilerError, RuntimeError};
+use crate::tokens::TokenType;
 use crate::value::Value;
 use std::collections::HashMap;
 use std::sync::LazyLock;
-use crate::builtins::string::string_methods;
-use crate::errors::RuntimeError;
+use crate::ast_compiler::Parameter;
+
+pub(crate) struct Signature {
+    pub(crate) parameters: Vec<Parameter>,
+    pub(crate) return_type: TokenType,
+    pub(crate) function: MethodFn,
+}
+
+impl Signature {
+    pub(crate) fn new(
+        parameters: Vec<Parameter>,
+        return_type: TokenType,
+        function: MethodFn,
+    ) -> Self {
+        Self {
+            parameters,
+            return_type,
+            function,
+        }
+    }
+
+    pub(crate) fn arity(&self) -> usize {
+        self.parameters.len()
+    }
+}
 
 pub(crate) type MethodFn = fn(Value, Vec<Value>) -> Result<Value, RuntimeError>;
-pub(crate) type MethodMap = HashMap<String, MethodFn>;
+pub(crate) type MethodMap = HashMap<String, Signature>;
 pub(crate) type MethodTable = HashMap<String, MethodMap>;
 
 static METHODS: LazyLock<MethodTable> = LazyLock::new(|| {
@@ -16,23 +42,26 @@ static METHODS: LazyLock<MethodTable> = LazyLock::new(|| {
     table
 });
 
-pub(crate) fn insert(m: &mut MethodMap, name: &str, method: MethodFn) {
+pub(crate) fn add(m: &mut MethodMap, name: &str, method: Signature) {
     m.insert(name.to_string(), method);
 }
 
-pub fn call(
+pub(crate) fn lookup(type_name: &str, method_name: &str) -> Result<&'static Signature, CompilerError> {
+     METHODS
+        .get(type_name)
+        .and_then(|methods| methods.get(method_name))
+        .ok_or_else(|| CompilerError::FunctionNotFound(format!("{}.{}", type_name, method_name)))
+}
+
+pub(crate) fn call(
     type_name: &str,
     method_name: &str,
     self_val: Value,
     args: Vec<Value>,
 ) -> Result<Value, RuntimeError> {
-    METHODS
-        .get(type_name)
-        .and_then(|methods| methods.get(method_name))
-        .ok_or_else(|| RuntimeError::FunctionNotFound(format!("{}.{}",type_name, method_name)))?
-        (self_val, args)
+    (lookup(type_name,method_name).map_err(|e|RuntimeError::FunctionNotFound(e.to_string()))?.function)(self_val, args)
 }
 
 pub(crate) fn expected(expected_type: &str) -> RuntimeError {
     RuntimeError::ExpectedType(expected_type.to_string())
-}
\ No newline at end of file
+}
diff --git a/src/builtins/string.rs b/src/builtins/string.rs
index f9e12e1..83d0c38 100644
--- a/src/builtins/string.rs
+++ b/src/builtins/string.rs
@@ -1,16 +1,45 @@
-use std::collections::HashMap;
-use crate::builtins::{expected, insert, MethodMap};
+use crate::builtins::{MethodMap, Parameter, Signature, add, expected};
 use crate::errors::RuntimeError;
-use crate::value::{bool, i64, string, Value};
+use crate::tokens::TokenType::{StringType, U64};
+use crate::value::{Value, bool, i64, string};
+use regex::Regex;
+use std::collections::HashMap;
 
 pub(crate) fn string_methods() -> MethodMap {
     let mut string_methods: MethodMap = HashMap::new();
     let m = &mut string_methods;
-    insert(m, "len", string_len);
-    insert(m, "to_uppercase", string_to_uppercase);
-    insert(m, "to_lowercase", string_to_lowercase);
-    insert(m, "contains", string_contains);
-    insert(m, "reverse", string_reverse);
+    add(m, "len", Signature::new(vec![], U64, string_len));
+    add(
+        m,
+        "to_uppercase",
+        Signature::new(vec![], StringType, string_to_uppercase),
+    );
+    add(
+        m,
+        "to_lowercase",
+        Signature::new(vec![], StringType, string_to_lowercase),
+    );
+    add(m, "contains", Signature::new(vec![], StringType, string_contains));
+    add(m, "reverse", Signature::new(vec![], StringType, string_reverse));
+    add(m, "trim", Signature::new(vec![], StringType, string_trim));
+    add(
+        m,
+        "trim_start",
+        Signature::new(vec![], StringType, string_trim_start),
+    );
+    add(m, "trim_end", Signature::new(vec![], StringType, string_trim_end));
+    add(
+        m,
+        "replace_all",
+        Signature::new(
+            vec![
+                Parameter::new("pattern", StringType),
+                Parameter::new("replacement", StringType),
+            ],
+            StringType,
+            string_replace_all,
+        ),
+    );
     string_methods
 }
 
@@ -37,22 +66,64 @@ fn string_to_lowercase(self_val: Value, _args: Vec<Value>) -> Result<Value, Runt
 
 fn string_contains(self_val: Value, args: Vec<Value>) -> Result<Value, RuntimeError> {
     match (self_val, args.first()) {
-        (Value::String(s), Some(Value::String(pat))) => {
-            Ok(bool(s.contains(pat.as_str())))
-        }
+        (Value::String(s), Some(Value::String(pat))) => Ok(bool(s.contains(pat.as_str()))),
         _ => Err(expected_a_string()),
     }
 }
 
 fn string_reverse(self_val: Value, _: Vec<Value>) -> Result<Value, RuntimeError> {
     match self_val {
-        Value::String(s) => {
-            Ok(s.chars().rev().collect::<String>().into())
-        }
+        Value::String(s) => Ok(s.chars().rev().collect::<String>().into()),
+        _ => Err(expected_a_string()),
+    }
+}
+
+fn string_trim(self_val: Value, _: Vec<Value>) -> Result<Value, RuntimeError> {
+    match self_val {
+        Value::String(s) => Ok(string(s.trim())),
+        _ => Err(expected_a_string()),
+    }
+}
+
+fn string_trim_start(self_val: Value, _: Vec<Value>) -> Result<Value, RuntimeError> {
+    match self_val {
+        Value::String(s) => Ok(string(s.trim_start())),
+        _ => Err(expected_a_string()),
+    }
+}
+
+fn string_trim_end(self_val: Value, _: Vec<Value>) -> Result<Value, RuntimeError> {
+    match self_val {
+        Value::String(s) => Ok(string(s.trim_end())),
+        _ => Err(expected_a_string()),
+    }
+}
+//TODO check arity in compiler (generically)
+fn string_replace_all(receiver: Value, args: Vec<Value>) -> Result<Value, RuntimeError> {
+    let pattern = if let Value::String(s) = &args[0] {
+        Regex::new(s).map_err(|_| RuntimeError::IllegalArgumentException("Invalid regex".into()))?
+    } else {
+        return Err(RuntimeError::IllegalArgumentException(
+            format!("Illegal pattern. Expected a string, but got {}", &args[0]).into(),
+        ));
+    };
+    let replacement = if let Value::String(repl) = &args[1] {
+        repl
+    } else {
+        return Err(RuntimeError::IllegalArgumentException(
+            format!(
+                "Illegal replacement. Expected a string but got {}",
+                &args[1]
+            )
+            .into(),
+        ));
+    };
+    match receiver {
+        Value::String(ref str) => Ok(string(pattern.replace_all(str, replacement))),
         _ => Err(expected_a_string()),
     }
 }
 
 fn expected_a_string() -> RuntimeError {
     expected("string")
-}
\ No newline at end of file
+}
diff --git a/src/bytecode_compiler.rs b/src/bytecode_compiler.rs
index 694ea72..878e632 100644
--- a/src/bytecode_compiler.rs
+++ b/src/bytecode_compiler.rs
@@ -1,5 +1,6 @@
 use crate::ast_compiler::Expression::NamedParameter;
 use crate::ast_compiler::{Expression, Function, Parameter, Statement};
+use crate::builtins::lookup;
 use crate::chunk::Chunk;
 use crate::errors::CompilerError::{IncompatibleTypes, UndeclaredVariable};
 use crate::errors::{CompilerError, CompilerErrorAtLine};
@@ -205,17 +206,24 @@ impl Compiler {
                 self.compile_expression(namespace, receiver, symbols, registry)?;
                 let receiver_type = infer_type(receiver, symbols).to_string();
 
-                let type_index = self
-                    .chunk
-                    .find_constant(&receiver_type)
-                    .unwrap_or_else(|| self.chunk.add_constant(Value::String(receiver_type)));
+                let type_index = self.chunk.find_constant(&receiver_type).unwrap_or_else(|| {
+                    self.chunk
+                        .add_constant(Value::String(receiver_type.clone()))
+                });
 
                 let name_index = self.chunk.find_constant(method_name).unwrap_or_else(|| {
                     self.chunk
                         .add_constant(Value::String(method_name.to_string()))
                 });
-                //TODO lookup parameters for builtin
-                self.get_arguments_in_order(namespace, symbols, registry, arguments, &vec![])?;
+                let signature = lookup(&receiver_type, method_name).map_err(|e| self.raise(e))?;
+
+                self.get_arguments_in_order(
+                    namespace,
+                    symbols,
+                    registry,
+                    arguments,
+                    &signature.parameters,
+                )?;
                 self.emit_byte(OP_CALL_BUILTIN);
                 self.emit_byte(name_index as u16);
                 self.emit_byte(type_index as u16);
@@ -312,19 +320,17 @@ impl Compiler {
         namespace: &str,
         symbols: &SymbolTable,
         registry: &mut Registry,
-        arguments: &Vec<Expression>,
-        parameters: &Vec<Parameter>,
+        arguments: &[Expression],
+        parameters: &[Parameter],
     ) -> Result<(), CompilerErrorAtLine> {
-        for parameter in parameters {
-            for argument in arguments {
+        for argument in arguments {
+            for parameter in parameters {
                 if let NamedParameter { name, value, .. } = argument {
                     if name.lexeme == parameter.name.lexeme {
                         let value_type = infer_type(value, symbols);
                         if parameter.var_type != value_type {
-                            return Err(self.raise(CompilerError::IncompatibleTypes(
-                                parameter.var_type.clone(),
-                                value_type,
-                            )));
+                            return Err(self
+                                .raise(IncompatibleTypes(parameter.var_type.clone(), value_type)));
                         } else {
                             self.compile_expression(namespace, argument, symbols, registry)?;
                             break;
diff --git a/src/compiler_tests.rs b/src/compiler_tests.rs
index cd4f3b9..81e3f07 100644
--- a/src/compiler_tests.rs
+++ b/src/compiler_tests.rs
@@ -1,6 +1,6 @@
 #[cfg(test)]
 mod tests {
-    use crate::value::Value;
+    use crate::value::{Value, string};
     use crate::{compile, run};
     use chrono::DateTime;
 
@@ -21,23 +21,20 @@ mod tests {
 
     #[test]
     fn literal_string() {
-        assert_eq!(run(r#""a""#), Ok(Value::String("a".into())));
+        assert_eq!(run(r#""a""#), Ok(string("a")));
     }
 
     #[test]
     fn literal_list() {
         assert_eq!(
             run(r#"["abc","def"]"#),
-            Ok(Value::List(vec![
-                Value::String("abc".into()),
-                Value::String("def".into())
-            ]))
+            Ok(Value::List(vec![string("abc"), string("def")]))
         );
     }
 
     #[test]
     fn index_in_list_literal() {
-        assert_eq!(run(r#"["abc","def"][1]"#), Ok(Value::String("def".into())))
+        assert_eq!(run(r#"["abc","def"][1]"#), Ok(string("def")))
     }
 
     #[test]
@@ -45,7 +42,7 @@ mod tests {
         assert_eq!(
             run(r#"let a:list = ["abc","def"]
 a[1]"#),
-            Ok(Value::String("def".into()))
+            Ok(string("def"))
         )
     }
 
@@ -118,7 +115,7 @@ a"#),
             run(r#"fn add_hello(name: string) -> string:
     "Hello " + name
 add_hello("world")"#),
-            Ok(Value::String("Hello world".to_string()))
+            Ok(string("Hello world"))
         );
     }
 
@@ -169,11 +166,11 @@ p"#);
         let result = result.unwrap();
         if let Value::Map(map) = result {
             assert_eq!(
-                map.get(&Value::String("name".to_string())).unwrap(),
-                &Value::String("Dent".to_string())
+                map.get(&string("name")).unwrap(),
+                &string("Dent")
             );
             assert_eq!(
-                map.get(&Value::String("age".to_string())).unwrap(),
+                map.get(&string("age")).unwrap(),
                 &Value::I64(40)
             );
         }
@@ -187,8 +184,8 @@ m"#);
         let result = result.unwrap();
         if let Value::Map(map) = result {
             assert_eq!(
-                map.get(&Value::String("name".to_string())).unwrap(),
-                &Value::String("Dent".to_string())
+                map.get(&string("name")).unwrap(),
+                &string("Dent")
             );
         }
     }
@@ -216,17 +213,17 @@ m["name"]"#);
 
     #[test]
     fn add_strings() {
-        assert_eq!(run(r#""a"+"b""#), Ok(Value::String("ab".into())));
+        assert_eq!(run(r#""a"+"b""#), Ok(string("ab")));
     }
 
     #[test]
     fn add_string_and_int() {
-        assert_eq!(run(r#""a"+42"#), Ok(Value::String("a42".into())));
+        assert_eq!(run(r#""a"+42"#), Ok(string("a42")));
     }
 
     #[test]
     fn add_string_and_bool() {
-        assert_eq!(run(r#""a"+false"#), Ok(Value::String("afalse".into())));
+        assert_eq!(run(r#""a"+false"#), Ok(string("afalse")));
     }
 
     #[test]
@@ -259,20 +256,25 @@ date"#),
     }
 
     #[test]
-    fn string_reverse(){
-        assert_eq!(run(r#""abc".reverse()"#), Ok(Value::String("cba".into())));
+    fn string_reverse() {
+        assert_eq!(run(r#""abc".reverse()"#), Ok(string("cba")));
     }
 
     #[test]
-    fn string_to_upper(){
-        assert_eq!(run(r#""abc".to_uppercase()"#), Ok(Value::String("ABC".into())));
+    fn string_to_upper() {
+        assert_eq!(run(r#""abc".to_uppercase()"#), Ok(string("ABC")));
     }
 
     #[test]
-    fn string_len(){
+    fn string_len() {
         assert_eq!(run(r#""abc".len()"#), Ok(Value::I64(3)));
     }
 
+    #[test]
+    fn string_replace() {
+        assert_eq!(run(r#""Hello".replace_all("l","p")"#), Ok(string("Heppo")));
+    }
+
     // #[test]
     // fn package() {
     //     assert_eq!(run(r#"a.b.c()"#), Ok(Value::U32(48)));
diff --git a/src/errors.rs b/src/errors.rs
index 3231734..87ea3d5 100644
--- a/src/errors.rs
+++ b/src/errors.rs
@@ -83,6 +83,8 @@ pub enum RuntimeError {
     FunctionNotFound(String),
     #[error("The number of of arguments for {0} is not correct. Should be {1}, got {2}")]
     IllegalArgumentsException(String,usize,usize),
+    #[error("{0}")]
+    IllegalArgumentException(String),
     #[error("Expected {0}")]
     ExpectedType(String),
 }
diff --git a/src/vm.rs b/src/vm.rs
index c01070c..c359ce6 100644
--- a/src/vm.rs
+++ b/src/vm.rs
@@ -194,7 +194,6 @@ impl Vm {
                     let function_type_index = self.read(chunk);
                     let receiver_type_name = chunk.constants[function_type_index].to_string();
 
-                    let receiver = self.pop();
                     let num_args = self.read(chunk);
                     let mut args = vec![];
                     for _ in 0..num_args {
@@ -202,6 +201,7 @@ impl Vm {
                         args.push(arg);
                     }
                     args.reverse();
+                    let receiver = self.pop();
                     let return_value = crate::builtins::call(&receiver_type_name, &function_name, receiver, args)?;
                     self.push(return_value);
                 }