diff --git a/.gitignore b/.gitignore
index 8ea0ee8..ea8c4bf 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,2 +1 @@
 /target
-result*
diff --git a/CHANGELOG.md b/CHANGELOG.md
index a155b60..840fc67 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -7,15 +7,6 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [unreleased]
 
-### Added
-
-- Packagin with Nix flakes (with nixpkgs buildRustPackage) [!16](https://gitlab.cern.ch/wotsubo/endcap-sl-software-ri-generator/-/merge_requests/16)
-- Now xml metadata can be overwritten with corresponding environmental variables. [!17](https://gitlab.cern.ch/wotsubo/endcap-sl-software-ri-generator/-/merge_requests/17)
-
-### Changed
-
-- Improve error message from syn in generator. !15
-
 ## [0.3.1] - 2025-04-11
 
 ### Changed
diff --git a/README-ja.md b/README-ja.md
index ddda1ba..7e770e3 100644
--- a/README-ja.md
+++ b/README-ja.md
@@ -33,7 +33,7 @@ cargo build --features=bin --bins --release
 
 `target/release`に入ってるバイナリファイルを実行するか、`cargo run -- <XML> <OUT>`で実行できます。
 
-詳しくは(`-h`ではなく)`--help`を見てください。
+詳しくは`--help`を見てください。
 
 ### ライブラリクレートの使い方
 
diff --git a/README.md b/README.md
index e9fd84e..9685c6f 100644
--- a/README.md
+++ b/README.md
@@ -36,7 +36,7 @@ to build.
 
 Execute the binary generated in `target/release/`, or run with `cargo run -- <XML> <OUT>`.
 
-See the `--help`(not `-h`) for more information.
+See the `--help` for more information.
 
 ### Library crate usage
 
diff --git a/flake.lock b/flake.lock
deleted file mode 100644
index d28d4ad..0000000
--- a/flake.lock
+++ /dev/null
@@ -1,82 +0,0 @@
-{
-  "nodes": {
-    "flake-utils": {
-      "inputs": {
-        "systems": "systems"
-      },
-      "locked": {
-        "lastModified": 1731533236,
-        "narHash": "sha256-l0KFg5HjrsfsO/JpG+r7fRrqm12kzFHyUHqHCVpMMbI=",
-        "owner": "numtide",
-        "repo": "flake-utils",
-        "rev": "11707dc2f618dd54ca8739b309ec4fc024de578b",
-        "type": "github"
-      },
-      "original": {
-        "owner": "numtide",
-        "repo": "flake-utils",
-        "type": "github"
-      }
-    },
-    "nixpkgs": {
-      "locked": {
-        "lastModified": 1744098102,
-        "narHash": "sha256-tzCdyIJj9AjysC3OuKA+tMD/kDEDAF9mICPDU7ix0JA=",
-        "owner": "nixos",
-        "repo": "nixpkgs",
-        "rev": "c8cd81426f45942bb2906d5ed2fe21d2f19d95b7",
-        "type": "github"
-      },
-      "original": {
-        "owner": "nixos",
-        "ref": "nixos-unstable",
-        "repo": "nixpkgs",
-        "type": "github"
-      }
-    },
-    "root": {
-      "inputs": {
-        "flake-utils": "flake-utils",
-        "nixpkgs": "nixpkgs",
-        "rust-overlay": "rust-overlay"
-      }
-    },
-    "rust-overlay": {
-      "inputs": {
-        "nixpkgs": [
-          "nixpkgs"
-        ]
-      },
-      "locked": {
-        "lastModified": 1744166053,
-        "narHash": "sha256-mpI7OzFwp+fUeDtZYQbVZ2YmtxTN2UNrrOwbYD27xKU=",
-        "owner": "oxalica",
-        "repo": "rust-overlay",
-        "rev": "896158be1835589db6f42f45ef0a49b8b492cc66",
-        "type": "github"
-      },
-      "original": {
-        "owner": "oxalica",
-        "repo": "rust-overlay",
-        "type": "github"
-      }
-    },
-    "systems": {
-      "locked": {
-        "lastModified": 1681028828,
-        "narHash": "sha256-Vy1rq5AaRuLzOxct8nz4T6wlgyUR7zLU309k9mBC768=",
-        "owner": "nix-systems",
-        "repo": "default",
-        "rev": "da67096a3b9bf56a91d16901293e51ba5b49a27e",
-        "type": "github"
-      },
-      "original": {
-        "owner": "nix-systems",
-        "repo": "default",
-        "type": "github"
-      }
-    }
-  },
-  "root": "root",
-  "version": 7
-}
diff --git a/flake.nix b/flake.nix
deleted file mode 100644
index 6a76064..0000000
--- a/flake.nix
+++ /dev/null
@@ -1,37 +0,0 @@
-{
-  description = "A very basic flake";
-
-  inputs = {
-    nixpkgs.url = "github:nixos/nixpkgs?ref=nixos-unstable";
-    flake-utils.url = "github:numtide/flake-utils";
-    rust-overlay = {
-      url = "github:oxalica/rust-overlay";
-      inputs.nixpkgs.follows = "nixpkgs";
-    };
-  };
-
-  outputs = 
-    {
-      nixpkgs,
-      flake-utils,
-      rust-overlay,
-      ...
-    }:
-    flake-utils.lib.eachDefaultSystem (
-      system:
-      let
-        pkgs = import nixpkgs {
-          inherit system;
-          overlays = [ rust-overlay.overlays.default ];
-        };
-      in
-      {
-        devShells.default = pkgs.mkShell {
-          packages = [
-            pkgs.rust-bin.stable.latest.default
-          ];
-        };
-        packages.default = pkgs.callPackage ./nix/endcap-sl-software-ri-generator.nix { };
-      }
-    );
-}
diff --git a/nix/endcap-sl-software-ri-generator.nix b/nix/endcap-sl-software-ri-generator.nix
deleted file mode 100644
index 0ffc9b7..0000000
--- a/nix/endcap-sl-software-ri-generator.nix
+++ /dev/null
@@ -1,11 +0,0 @@
-{ rustPlatform }:
-# https://nixos.org/manual/nixpkgs/stable/#rust
-rustPlatform.buildRustPackage {
-  pname = "endcap-sl-software-ri-generator";
-  version = "0.3.0";
-
-  src = ../.;
-  cargoLock.lockFile = ../Cargo.lock;
-
-  buildFeatures = [ "bin" ];
-}
diff --git a/src/generator.rs b/src/generator.rs
index 110e4f1..f4487b4 100644
--- a/src/generator.rs
+++ b/src/generator.rs
@@ -26,12 +26,8 @@ use thiserror::Error;
 
 #[derive(Debug, Error)]
 pub enum CodeGenError {
-    #[error("tokenization(syn) error: {source}: {code}")]
-    SynError {
-        #[source]
-        source: syn::Error,
-        code: String,
-    },
+    #[error("tokenization(syn) error")]
+    SynError(#[from] syn::Error),
     #[error("failed to create file (name duplicated): {0}")]
     FilePathDuplicatedError(String),
     #[error("parent is required for {module}")]
@@ -46,17 +42,11 @@ mod util {
     use super::CodeGenError;
 
     pub(super) fn parse_to_ident(s: &str) -> Result<proc_macro2::Ident, CodeGenError> {
-        syn::parse_str(s).map_err(|e| CodeGenError::SynError {
-            source: e,
-            code: s.to_string(),
-        })
+        Ok(syn::parse_str(s)?)
     }
 
     pub(super) fn parse_to_literal(s: &str) -> Result<proc_macro2::Literal, CodeGenError> {
-        syn::parse_str(s).map_err(|e| CodeGenError::SynError {
-            source: e,
-            code: s.to_string(),
-        })
+        Ok(syn::parse_str(s)?)
     }
 
     // currently only U32 is used, so `dead_code` for Debug, PartialEq
@@ -171,29 +161,27 @@ This code is auto generated using endcap_sl_software_ri_generator.
             GENERATOR_GIT_SHA,
         );
         let files = self.generate_register_interface(None, None, HashMap::new())?;
-        files
+        Ok(files
             .into_iter()
-            .map(|(path, tokens)| -> Result<(PathBuf, syn::File), _> {
-                let tokens = if path
-                    .file_name()
-                    .is_some_and(|file| file == "register_interface.rs")
-                {
-                    quote! {
-                        #![doc = #build_metadata]
+            .map(
+                |(path, tokens)| -> Result<(PathBuf, syn::File), syn::Error> {
+                    let tokens = if path
+                        .file_name()
+                        .is_some_and(|file| file == "register_interface.rs")
+                    {
+                        quote! {
+                            #![doc = #build_metadata]
 
-                        #tokens
-                    }
-                } else {
-                    tokens
-                };
-                let file: syn::File =
-                    syn::parse2(tokens.clone()).map_err(|e| CodeGenError::SynError {
-                        source: e,
-                        code: tokens.to_string(),
-                    })?;
-                Ok((path, file))
-            })
-            .process_results(|kv| HashMap::from_iter(kv))
+                            #tokens
+                        }
+                    } else {
+                        tokens
+                    };
+                    let file: syn::File = syn::parse2(tokens)?;
+                    Ok((path, file))
+                },
+            )
+            .process_results(|kv| HashMap::from_iter(kv))?)
     }
 }
 
diff --git a/src/io.rs b/src/io.rs
index bdf712f..8b2b1eb 100644
--- a/src/io.rs
+++ b/src/io.rs
@@ -1,15 +1,11 @@
 //! File IO for generated codes.
 
-use std::{collections::HashMap, env, ffi::OsString, fs, io, path, process};
+use std::{collections::HashMap, fs, io, path, process};
 
 use thiserror::Error;
 
 use crate::types::XmlGitInfo;
 
-const ENVVAR_XML_GIT_DESCRIBE: &str = "XML_GIT_DESCRIBE";
-const ENVVAR_XML_GIT_TIMESTAMP: &str = "XML_GIT_TIMESTAMP";
-const ENVVAR_XML_GIT_SHA: &str = "XML_GIT_SHA";
-
 #[derive(Debug, Error)]
 pub enum XmlGitInfoError {
     #[error("io error while getting xml git info: {msg} {source}")]
@@ -20,8 +16,6 @@ pub enum XmlGitInfoError {
     },
     #[error("git failed: {msg}: {stderr}")]
     CommandFailed { msg: &'static str, stderr: String },
-    #[error("env var {var} is not unicode: {}", s.to_string_lossy())]
-    NotUnicodeEnvVar { var: &'static str, s: OsString },
 }
 
 impl XmlGitInfoError {
@@ -31,84 +25,44 @@ impl XmlGitInfoError {
 }
 
 pub(crate) fn get_xml_gitinfo(xml_path: &path::Path) -> Result<XmlGitInfo, XmlGitInfoError> {
-    let describe = match env::var(ENVVAR_XML_GIT_DESCRIBE) {
-        Ok(describe) => describe,
-        Err(env::VarError::NotUnicode(s)) => {
-            return Err(XmlGitInfoError::NotUnicodeEnvVar {
-                var: ENVVAR_XML_GIT_DESCRIBE,
-                s,
-            });
-        }
-        Err(env::VarError::NotPresent) => {
-            let out_describe = process::Command::new("git")
-                .args(["describe", "--always", "--dirty"])
-                .current_dir(xml_path.parent().unwrap())
-                .output()
-                .map_err(|e| XmlGitInfoError::io_error(e, "git describe"))?;
-            let describe = if out_describe.status.success() {
-                String::from_utf8_lossy(&out_describe.stdout)
-                    .trim()
-                    .to_owned()
-            } else {
-                return Err(XmlGitInfoError::CommandFailed {
-                    msg: "git describe",
-                    stderr: String::from_utf8_lossy(&out_describe.stderr).into_owned(),
-                });
-            };
-            describe
-        }
+    let describe = process::Command::new("git")
+        .args(["describe", "--always", "--dirty"])
+        .current_dir(xml_path.parent().unwrap())
+        .output()
+        .map_err(|e| XmlGitInfoError::io_error(e, "git describe"))?;
+    let describe = if describe.status.success() {
+        String::from_utf8_lossy(&describe.stdout).trim().to_owned()
+    } else {
+        return Err(XmlGitInfoError::CommandFailed {
+            msg: "git describe",
+            stderr: String::from_utf8_lossy(&describe.stderr).into_owned(),
+        });
     };
-    let timestamp = match env::var(ENVVAR_XML_GIT_TIMESTAMP) {
-        Ok(timestamp) => timestamp,
-        Err(env::VarError::NotUnicode(s)) => {
-            return Err(XmlGitInfoError::NotUnicodeEnvVar {
-                var: ENVVAR_XML_GIT_TIMESTAMP,
-                s,
-            });
-        }
-        Err(env::VarError::NotPresent) => {
-            let timestamp_out = process::Command::new("git")
-                .args(["log", "-1", "--pretty=format:'%cI'"])
-                .current_dir(xml_path.parent().unwrap())
-                .output()
-                .map_err(|e| XmlGitInfoError::io_error(e, "git log (timestamp)"))?;
-            let timestamp = if timestamp_out.status.success() {
-                String::from_utf8_lossy(&timestamp_out.stdout)
-                    .trim()
-                    .to_owned()
-            } else {
-                return Err(XmlGitInfoError::CommandFailed {
-                    msg: "git log (timestamp)",
-                    stderr: String::from_utf8_lossy(&timestamp_out.stderr).into_owned(),
-                });
-            };
-            timestamp
-        }
+    let timestamp = process::Command::new("git")
+        .args(["log", "-1", "--pretty=format:'%cI'"])
+        .current_dir(xml_path.parent().unwrap())
+        .output()
+        .map_err(|e| XmlGitInfoError::io_error(e, "git log (timestamp)"))?;
+    let timestamp = if timestamp.status.success() {
+        String::from_utf8_lossy(&timestamp.stdout).trim().to_owned()
+    } else {
+        return Err(XmlGitInfoError::CommandFailed {
+            msg: "git log (timestamp)",
+            stderr: String::from_utf8_lossy(&timestamp.stderr).into_owned(),
+        });
     };
-    let git_sha = match env::var(ENVVAR_XML_GIT_SHA) {
-        Ok(sha) => sha,
-        Err(env::VarError::NotUnicode(s)) => {
-            return Err(XmlGitInfoError::NotUnicodeEnvVar {
-                var: ENVVAR_XML_GIT_SHA,
-                s,
-            });
-        }
-        Err(env::VarError::NotPresent) => {
-            let sha = process::Command::new("git")
-                .args(["rev-parse", "HEAD"])
-                .current_dir(xml_path.parent().unwrap())
-                .output()
-                .map_err(|e| XmlGitInfoError::io_error(e, "git rev-parse (sha)"))?;
-            let git_sha = if sha.status.success() {
-                String::from_utf8_lossy(&sha.stdout).trim().to_owned()
-            } else {
-                return Err(XmlGitInfoError::CommandFailed {
-                    msg: "git rev-parse (sha)",
-                    stderr: String::from_utf8_lossy(&sha.stderr).into_owned(),
-                });
-            };
-            git_sha
-        }
+    let sha = process::Command::new("git")
+        .args(["rev-parse", "HEAD"])
+        .current_dir(xml_path.parent().unwrap())
+        .output()
+        .map_err(|e| XmlGitInfoError::io_error(e, "git rev-parse (sha)"))?;
+    let git_sha = if sha.status.success() {
+        String::from_utf8_lossy(&sha.stdout).trim().to_owned()
+    } else {
+        return Err(XmlGitInfoError::CommandFailed {
+            msg: "git rev-parse (sha)",
+            stderr: String::from_utf8_lossy(&sha.stderr).into_owned(),
+        });
     };
     Ok(XmlGitInfo {
         describe,
diff --git a/src/main.rs b/src/main.rs
index 6208678..01ca8e7 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -3,16 +3,11 @@ use std::path;
 use anyhow::Result;
 use clap::{Parser, Subcommand};
 
-/// Validate the register map xml and generate register interface from register map xml.
-/// See `help` with each commands to see detailed explanations.
+/// Generate register interface from register map xml.
 #[derive(Parser, Debug)]
-#[command(version, about, long_about)]
+#[command(version, about)]
 struct Args {
     /// Input XML register map.
-    ///
-    /// The path must be a valid git repository to get git metadata.
-    /// You can also force these metadata with environmental variables `XML_GIT_DESCRIBE`,
-    /// `XML_GIT_TIMESTAMP` and `XML_GIT_SHA`.
     xml: path::PathBuf,
     #[command(subcommand)]
     command: Commands,
@@ -28,8 +23,6 @@ enum Commands {
         out: path::PathBuf,
     },
     /// Generate flattened register map in CSV.
-    ///
-    /// Also run validation before generation.
     #[cfg(feature = "flatmap")]
     Flatmap {
         /// Flattened csv out path.