diff --git a/Cargo.toml b/Cargo.toml
index 0e384e7..7586878 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -28,3 +28,6 @@ lto = true          # Enable link-time optimization
 codegen-units = 1   # Reduce number of codegen units to increase optimizations
 panic = 'abort'     # Abort on panic
 strip = true        # Strip symbols from binary
+# for performance profiling
+# strip = false
+# debug = true
diff --git a/README.md b/README.md
index aebc2c3..095fd45 100644
--- a/README.md
+++ b/README.md
@@ -21,15 +21,24 @@ to export data into (CSV) files or import data from (CSV) files.
 ## Installation
 
 ### With Cargo ([Rust toolchain](https://www.rust-lang.org/learn/get-started))
+
 ```bash
 cargo install sw-sync-cli
 ```
 Same command can be used for updates. See [crate](https://crates.io/crates/sw-sync-cli)
 
 ### Manual
+
 head to [GitHub releases](https://github.com/MalteJanz/sw-sync-cli/releases) and download the right binary for your operating system.
 Then either execute the binary directly or put it in your `PATH`.
 
+### Build it from this repository
+
+1. Clone this repository
+2. Have the latest [Rust toolchain](https://www.rust-lang.org/learn/get-started) installed
+3. Run `cargo build --release` inside the repository root folder
+4. You will get your executable here `./target/release/sw-sync-cli`
+
 ## Usage
 
 1. Set up an [integration](https://docs.shopware.com/en/shopware-6-en/settings/system/integrationen?category=shopware-6-en/settings/system) inside shopware.
diff --git a/src/api/mod.rs b/src/api/mod.rs
index 1cef6f3..139a915 100644
--- a/src/api/mod.rs
+++ b/src/api/mod.rs
@@ -248,12 +248,12 @@ impl SwClient {
     }
 
     async fn deserialize<T: for<'a> Deserialize<'a>>(response: Response) -> Result<T, SwApiError> {
-        let text = response.text().await?;
+        let bytes = response.bytes().await?;
 
-        match serde_json::from_str(&text) {
+        match serde_json::from_slice(&bytes) {
             Ok(t) => Ok(t),
             Err(_e) => {
-                let body: serde_json::Value = serde_json::from_str(&text)?;
+                let body: serde_json::Value = serde_json::from_slice(&bytes)?;
                 Err(SwApiError::DeserializeIntoSchema(
                     serde_json::to_string_pretty(&body)?,
                 ))
diff --git a/src/cli.rs b/src/cli.rs
index c229554..2e67733 100644
--- a/src/cli.rs
+++ b/src/cli.rs
@@ -52,7 +52,7 @@ pub enum Commands {
         // #[arg(short, long, action = ArgAction::SetTrue)]
         // verbose: bool,
         /// How many requests can be "in-flight" at the same time
-        #[arg(short, long, default_value = "8")]
+        #[arg(short, long, default_value = "10")]
         in_flight_limit: usize,
     },
 }
diff --git a/src/data/transform/mod.rs b/src/data/transform/mod.rs
index b5ccfef..c6519a6 100644
--- a/src/data/transform/mod.rs
+++ b/src/data/transform/mod.rs
@@ -26,10 +26,12 @@ pub fn deserialize_row(
                 let column_index = headers
                     .iter()
                     .position(|header| header == path_mapping.file_column)
-                    .context(format!(
-                        "Can't find column '{}' in CSV headers",
-                        path_mapping.file_column
-                    ))?;
+                    .with_context(|| {
+                        format!(
+                            "Can't find column '{}' in CSV headers",
+                            path_mapping.file_column
+                        )
+                    })?;
 
                 let raw_value = row
                     .get(column_index)
@@ -56,10 +58,10 @@ pub fn serialize_entity(entity: Entity, context: &SyncContext) -> anyhow::Result
         match mapping {
             Mapping::ByPath(path_mapping) => {
                 let value = entity.get_by_path(&path_mapping.entity_path)
-                    .context(format!(
+                    .with_context(|| format!(
                         "could not get field path '{}' specified in mapping (you might try the optional chaining operator '?.' to fallback to null), entity attributes:\n{}",
                         path_mapping.entity_path,
-                        serde_json::to_string_pretty(&entity).unwrap())
+                        serde_json::to_string_pretty(&entity).unwrap()) // expensive for big entities
                     )?;
 
                 let value_str = match value {
@@ -72,10 +74,12 @@ pub fn serialize_entity(entity: Entity, context: &SyncContext) -> anyhow::Result
             Mapping::ByScript(script_mapping) => {
                 let value = script_row
                     .get(script_mapping.key.as_str())
-                    .context(format!(
-                        "failed to retrieve script key '{}' of row",
-                        script_mapping.key
-                    ))?;
+                    .with_context(|| {
+                        format!(
+                            "failed to retrieve script key '{}' of row",
+                            script_mapping.key
+                        )
+                    })?;
                 let value_str = serde_json::to_string(value)?;
 
                 row.push(value_str);
diff --git a/src/data/transform/script.rs b/src/data/transform/script.rs
index f5190be..6379aa3 100644
--- a/src/data/transform/script.rs
+++ b/src/data/transform/script.rs
@@ -6,7 +6,7 @@ use crate::SyncContext;
 use anyhow::Context;
 use csv::StringRecord;
 use rhai::packages::{BasicArrayPackage, CorePackage, MoreStringPackage, Package};
-use rhai::{Engine, Position, Scope, AST};
+use rhai::{Engine, OptimizationLevel, Position, Scope, AST};
 
 #[derive(Debug)]
 pub struct ScriptingEnvironment {
@@ -37,10 +37,9 @@ impl ScriptingEnvironment {
             let column_index = headers
                 .iter()
                 .position(|h| h == mapping.file_column)
-                .context(format!(
-                    "Can't find column '{}' in CSV headers",
-                    mapping.file_column
-                ))?;
+                .with_context(|| {
+                    format!("Can't find column '{}' in CSV headers", mapping.file_column)
+                })?;
 
             let value = row
                 .get(column_index)
@@ -78,7 +77,11 @@ impl ScriptingEnvironment {
         };
 
         let mut scope = Scope::new();
+
+        // this is potentially expensive for big entities!
+        // we might only want to pass some data into the script...
         let script_entity = rhai::serde::to_dynamic(entity)?;
+
         scope.push_dynamic("entity", script_entity);
         let row_dynamic = rhai::Map::new();
         scope.push("row", row_dynamic);
@@ -124,6 +127,8 @@ pub fn prepare_scripting_environment(
 
 fn get_base_engine() -> Engine {
     let mut engine = Engine::new_raw();
+    engine.set_optimization_level(OptimizationLevel::Full);
+
     // Default print/debug implementations
     engine.on_print(|text| println!("{text}"));
     engine.on_debug(|text, source, pos| match (source, pos) {