diff --git a/Cargo.toml b/Cargo.toml
index 80b359f..71e31a7 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -53,6 +53,7 @@ h3 = { git = "https://github.com/hyperium/h3.git" }
 h3-quinn = { git = "https://github.com/hyperium/h3.git" }
 bytes = "1.1.0"
 mimalloc-rust = "0.2.0"
+thiserror = "1.0.31"
 
 
 [dev-dependencies]
diff --git a/src/backend.rs b/src/backend.rs
index 4cbbdee..8d58d8c 100644
--- a/src/backend.rs
+++ b/src/backend.rs
@@ -18,7 +18,7 @@ pub type ServerNameLC = Vec<u8>;
 pub type PathNameLC = Vec<u8>;
 
 pub struct Backends {
-  pub apps: HashMap<ServerNameLC, Backend>, // TODO: hyper::uriで抜いたhostで引っ掛ける。Stringでいいのか？
+  pub apps: HashMap<ServerNameLC, Backend>, // hyper::uriで抜いたhostで引っ掛ける
   pub default_server_name: Option<ServerNameLC>, // for plaintext http
 }
 
@@ -35,7 +35,7 @@ pub struct Backend {
 
 #[derive(Debug, Clone)]
 pub struct ReverseProxy {
-  pub upstream: HashMap<PathNameLC, Upstream>,
+  pub upstream: HashMap<PathNameLC, Upstream>, // TODO: HashMapでいいのかは疑問。max_by_keyでlongest prefix matchしてるのも無駄っぽいが。。。
 }
 
 impl ReverseProxy {
@@ -182,12 +182,7 @@ impl Backend {
         )
       })?;
       reader.set_position(0);
-      let mut rsa_keys = rustls_pemfile::rsa_private_keys(&mut reader).map_err(|_| {
-        io::Error::new(
-          io::ErrorKind::InvalidInput,
-          "Unable to parse the certificates private keys (RSA)",
-        )
-      })?;
+      let mut rsa_keys = rustls_pemfile::rsa_private_keys(&mut reader)?;
       let mut keys = pkcs8_keys;
       keys.append(&mut rsa_keys);
       if keys.is_empty() {
diff --git a/src/config/toml.rs b/src/config/toml.rs
index b7ecb7b..784da8c 100644
--- a/src/config/toml.rs
+++ b/src/config/toml.rs
@@ -64,13 +64,8 @@ impl UpstreamParams {
 
 impl ConfigToml {
   pub fn new(config_file: &str) -> Result<Self> {
-    let config_str = if let Ok(s) = fs::read_to_string(config_file) {
-      s
-    } else {
-      bail!("Failed to read config file");
-    };
-    let parsed: Result<ConfigToml> = toml::from_str(&config_str)
-      .map_err(|e: toml::de::Error| anyhow!("Failed to parse toml config: {:?}", e));
-    parsed
+    let config_str = fs::read_to_string(config_file).context("Failed to read config file")?;
+
+    toml::from_str(&config_str).context("Failed to parse toml config")
   }
 }
diff --git a/src/error.rs b/src/error.rs
index 6ac9a6b..4b30b2d 100644
--- a/src/error.rs
+++ b/src/error.rs
@@ -1 +1,12 @@
-pub use anyhow::{anyhow, bail, ensure, Context, Error, Result};
+pub use anyhow::{anyhow, bail, ensure, Context, Result};
+// use thiserror::Error;
+
+// #[allow(clippy::enum_variant_names)]
+// #[derive(Debug, Error)]
+// pub enum RpxyError {
+//   // IoError,
+//   #[error("ConfigError: {0}")]
+//   ConfigError(String),
+//   // ConnectionError,
+//   // HttpError,
+// }